title: A quantum mechanical model of the Riemann zeros

abstract:
  In 1999 Berry and Keating showed that a regularization of the 1D classical
Hamiltonian H = xp gives semiclassically the smooth counting function of the
Riemann zeros. In this paper we first generalize this result by considering a
phase space delimited by two boundary functions in position and momenta, which
induce a fluctuation term in the counting of energy levels. We next quantize
the xp Hamiltonian, adding an interaction term that depends on two wave
functions associated to the classical boundaries in phase space. The general
model is solved exactly, obtaining a continuum spectrum with discrete bound
states embbeded in it. We find the boundary wave functions, associated to the
Berry-Keating regularization, for which the average Riemann zeros become
resonances. A spectral realization of the Riemann zeros is achieved exploiting
the symmetry of the model under the exchange of position and momenta which is
related to the duality symmetry of the zeta function. The boundary wave
functions, giving rise to the Riemann zeros, are found using the Riemann-Siegel
formula of the zeta function. Other Dirichlet L-functions are shown to find a
natural realization in the model.

categories: math-ph cond-mat.other hep-th math.MP math.NT quant-ph


title: Orbit projections of proper Lie groupoids as fibrations

abstract:
  Let $\mathcal{G} \rightrightarrows M$ be a source locally trivial proper Lie
groupoid such that each orbit is of finite type. The orbit projection $M \to
M/\mathcal{G}$ is a fibration if and only if $\mathcal{G} \rightrightarrows M$
is regular.


title: System reliability and weighted lattice polynomials

abstract:
  The lifetime of a system of connected units under some natural assumptions
can be represented as a random variable Y defined as a weighted lattice
polynomial of random lifetimes of its components. As such, the concept of a
random variable Y defined by a weighted lattice polynomial of (lattice-valued)
random variables is considered in general and in some special cases. The
central object of interest is the cumulative distribution function of Y. In
particular, numerous results are obtained for lattice polynomials and weighted
lattice polynomials in case of independent arguments and in general. For the
general case, the technique consists in considering the joint probability
generating function of "indicator" variables. A connection is studied between Y
and order statistics of the set of arguments.


title: Transfer Principle for the Fundamental Lemma

abstract:
  The purpose of this paper is to explain how the identities of various
fundamental lemmas fall within the scope of the transfer principle, a general
result that allows to transfer theorems about identities of p-adic integrals
from one collection of fields to others. In particular, once the fundamental
lemma has been established for one collection of fields (for example, fields of
positive characteristic), it is also valid for others (fields of characteristic
zero).


title: New water masers in Seyfert and FIR bright galaxies. II

abstract:
  Recently, a relationship between the water maser detection rate and far
infrared (FIR) flux density has been found as a result of a 22 GHz maser survey
in a sample comprised of northern galaxies with 100 micron flux density > 50 Jy
and a declination >-30 degrees. The survey has been extended toward galaxies
with lower FIR flux densities in order to confirm this correlation and to
discover additional maser sources for relevant follow-up interferometric
studies. A sample of 41 galaxies with 30 Jy < S(100 micron) < 50 Jy and Dec. >
-30 degrees was observed with the 100-m telescope at Effelsberg in a search for
the 22 GHz water vapor line. The average 3-sigma noise level of the survey is
40 mJy for a 1 km/s channel, corresponding to a detection threshold for the
isotropic maser luminosity of about 0.5 solar luminosities at a distance of 25
Mpc. Two detections are reported: a megamaser with an isotropic luminosity of
approximately 35 solar luminosities in the Seyfert/HII galaxy NGC613 and a
kilomaser of approximately 1 solar luminosity in the merger system
NGC520.[abridged]


title: Canonical Functional Quantization of Pseudo-Photons in Planar Systems

abstract:
  Extended $U_e(1)\times U_g(1)$ electromagnetism containing both a photon and
a pseudo-photon is introduced at variational level and is justified by the
violation of the Bianchi identities in conceptual systems, either in the
presence of magnetic monopoles or non-regular external fields, not being
accounted by the standard Maxwell Lagrangian. It is carried a dimensional
reduction that renders a $U_e(1)\times U_g(1)$ Maxwell-BF type theory and it is
considered canonical functional quantization in planar systems which may be
relevant in Hall systems.


title: Pseudo-Photon Radiative Corrections in Non-Regular Backgrounds

abstract:
  Extended $U_e(1)\times U_g(1)$ electromagnetism containing both a photon and
a pseudo-photon is introduced at variational level and is justified by the
violation of the Bianchi identities in conceptual systems, either in the
presence of magnetic monopoles or non-regular external fields, not being
accounted by the standard Maxwell action. It is shown that in the perturbative
quantum field theory regimes there are observable consequences both for the
magnetic momenta and second order vacuum polarization radiative corrections in
the presence of non-regular strong electromagnetic fields (e.g. rotating
magnetic fields).


title: Stellar Subsystems of the Galaxy NGC 2366

abstract:
  Hubble Space Telescope archive data are used to perform photometry of stars
in seven fields at the center and periphery of the galaxy NGC2366. The
variation of the number density of stars of various ages with galactocentric
radius and along the minor axis of the galaxy are determined. The boundaries of
the thin and thick disks of the galaxy are found. The inferred sizes of the
subsystems of NGC2366 ($Z_{thin} = 4$ kpc and $Z_{thick} = 8$ kpc for the thin
and thick disks, respectively) are more typical for spiral galaxies. Evidence
for a stellar halo is found at the periphery of NGC2366 beyond the thick disk
of the galaxy.


title:
All static spherically symmetric anisotropic solutions of Einstein's
  equations

abstract:
  An algorithm recently presented by Lake to obtain all static spherically
symmetric perfect fluid solutions, is extended to the case of locally
anisotropic fluids (principal stresses unequal). As expected, the new formalism
requires the knowledge of two functions (instead of one) to generate all
possible solutions. To illustrate the method some known cases are recovered.


title:
Word-sheet corrections to dyons in string theories: A laboratory for the
  strong OSV conjecture

abstract:
  The explicit computation of arXiv:hep-th/0112157 and arXiv:hep-th/0108106
prove that all the cubic alpha-prime corrections to the backgrounds composed of
metric, NS two-form and dilaton can not be written in term of the modified
Riemann tensor where the field strength of the NS two form plays the role of
torsion. So the outcome of this writing has been trivial.


title:
An iterated search for influence from the future on the Large Hadron
  Collider

abstract:
  We analyse an iterated version of Nielsen and Ninomiya (N&N)'s proposed card
game experiment to search for a specific type of backward causation on the
running of the Large Hadron Collider (LHC) at CERN. We distinguish "endogenous"
and "exogenous" potential causes of failure of LHC and we discover a curious
"cross-talk" between their respective probabilities and occurrence timescales
when N&N-style backward causation is in effect. Finally, we note a kind of
"statistical cosmic censorship" preventing the influence from the future from
showing up in a statistical analysis of the iterated runs.


title:
Magnetotransport in low-density $p$-Si/SiGe heterostructures: From metal
  through hopping insulator to Wigner glass

abstract:
  We study DC and AC transport in low-density $p-$Si/SiGe heterostructures at
low temperatures and in a broad domain of magnetic fields up to 18 T. Complex
AC conductance is determined from simultaneous measurement of velocity and
attenuation of a surface acoustic wave propagating in close vicinity of the 2D
hole layer. The observed behaviors of DC and AC conductance are interpreted as
an evolution from metallic conductance at B=0 through hopping between localized
states in intermediate magnetic fields (close to the plateau of the integer
quantum Hall effect corresponding to the Landau-level filling factor $\nu$=1)
to formation of the Wigner glass in the extreme quantum limit ($B\gtrsim 14$,
$T \lesssim 0.8$ K).


title:
All-optical production of 7Li Bose-Einstein condensation using Feshbach
  resonances

abstract:
  We show an all-optical method of making 7Li condensate using tunability of
the scattering length in the proximity of a Feshbach resonance. We report the
observation of two new Feshbach resonances on |F = 1;mF = 0> state. The narrow
(broad) resonance of 7 G (34 G) width is detected at 831 +- 4 G (884 +4 -13 G).
Position of the scattering length zero crossing between the resonances is found
at 836 +- 4 G. The broad resonance is shown to be favorable for run away
evaporation which we perform in a crossed-beam optical dipole trap. Starting
directly form the phase space density of a magneto-optical trap we observe a
Bose-Einstein condensation threshold in less than 3 s of forced evaporation.


title:
Interacting coronae of two T Tauri stars: first observational evidence
  for solar-like helmet streamers

abstract:
  Context {The young binary system V773 Tau A exhibits a persistent radio
flaring activity that gradually increases from a level of a few mJy at
apoastron to more than 100 mJy at periastron. Interbinary collisions between
very large (> 15 R) magnetic structures anchored on the two rotating stars of
the system have been proposed to be the origin of these periodic radio flares.
Magnetic structures extended over tens of stellar radii, that can also account
for the observed fast decay of the radio flares, seem to correspond to the
typical solar semi-open quite extended magnetic configurations called helmet
streamers.} Aims {We aim to find direct observational evidence for the
postulated, solar-like, coronal topologies.} Methods {We performed
seven-consecutive-day VLBI observations at 8.4 GHz using an array consisting of
the VLBA and the 100-m Effelsberg telescope.} Results {Two distintive
structures appear in the radio images here presented. They happen to be
associated with the primary and secondary stars of the V773 Tau A system. In
one image (Fig.2-B) the two features are extended up to 18 R each and are
nearly parallel revealing the presence of two interacting helmet streamers. One
image (Fig.2-E) taken a few hours after a flare monitored by the 100-m
Effelsberg telescope shows one elongated fading structure substantially rotated
with respect to those seen in the B run. The same decay scenario is seen in
Fig.2-G for the helmet streamer associated with the other star.} Conclusions
{This is the very first direct evidence revealing that even if the flare origin
is magnetic reconnection due to interbinary collision, both stars independently
emit in the radio range with structures of their own. These structures are
helmet streamers, observed for the first time in stars other than the Sun.}


title: Dissipative discrete breathers in rf SQUID metamaterials

abstract:
  The existence and stability of dissipative discrete breathers (DDBs) in rf
superconducting quantum interference device (SQUID) arrays in both one and two
dimensions is investigated numerically. In an rf SQUID array, the nonlinearity
which is intrinsic to each SQUID due to the presence of the Josephson junction
(on-site nonlinearity), along with the weak coupling of each SQUID to its
nearest neighbors through magnetic forces, result in the appearance of discrete
breathers. We analyze several discrete breather excitations, both in one and
two dimensions, which are subjected to unavoidable losses. These losses,
however, are counter-balanced by an external flux source leading to linearly
stable discrete breather structures up to relatively large coupling parameters.
We show that DDB excitations may locally alter the magnetic response of array
from paramagnetic to diamagnetic or vice versa, and that they are not destroyed
by increasing the dimensionality.


title:
Self-guided wakefield experiments driven by petawatt class ultra-short
  laser pulses

abstract:
  We investigate the extension of self-injecting laser wakefield experiments to
the regime that will be accessible with the next generation of petawatt class
ultra-short pulse laser systems. Using linear scalings, current experimental
trends and numerical simulations we determine the optimal laser and target
parameters, i.e. focusing geometry, plasma density and target length, that are
required to increase the electron beam energy (to > 1 GeV) without the use of
external guiding structures.


title: Asymptotically optimal multistage tests of simple hypotheses

abstract:
  A family of variable stage size multistage tests of simple hypotheses is
described, based on efficient multistage sampling procedures. Using a loss
function that is a linear combination of sampling costs and error
probabilities, these tests are shown to minimize the integrated risk to second
order as the costs per stage and per observation approach zero. A numerical
study shows significant improvement over group sequential tests in a binomial
testing problem.


title:
Classical capacity of quantum channels with general Markovian correlated
  noise

abstract:
  The classical capacity of a quantum channel with arbitrary Markovian
correlated noise is evaluated. For the general case of a channel with long-term
memory, which corresponds to a Markov chain which does not converge to
equilibrium, the capacity is expressed in terms of the communicating classes of
the Markov chain. For an irreducible and aperiodic Markov chain, the channel is
forgetful, and one retrieves the known expression for the capacity.


title: Dominance of a Rational Map to the Coble Quartic

abstract:
  We show the dominance of the restriction map from a moduli space of stable
sheaves on the projective plane to the Coble quartic. With the dominance and
the interpretation of a stable sheaf on the plane in terms of the hyperplane
arrangements, we expect to investigate the geometry of the Coble quartic.


title: Understanding the small object argument

abstract:
  The small object argument is a transfinite construction which, starting from
a set of maps in a category, generates a weak factorisation system on that
category. As useful as it is, the small object argument has some problematic
aspects: it possesses no universal property; it does not converge; and it does
not seem to be related to other transfinite constructions occurring in
categorical algebra. In this paper, we give an "algebraic" refinement of the
small object argument, cast in terms of Grandis and Tholen's natural weak
factorisation systems, which rectifies each of these three deficiencies.


title: Seismic evolution of low/intermediate mass PMS stars

abstract:
  This article presents a study of the evolution of the internal structure and
seismic properties expected for low/intermediate mass Pre-Main Sequence (PMS)
stars. Seismic and non-seismic properties of PMS stars were analysed. This was
done using 0.8 to 4.4M$_\odot$ stellar models at stages ranging from the end of
the Hayashi track up to the Zero-Age Main-Sequence (ZAMS). This research
concludes that, for intermediate-mass stars (M$>$1.3M$_\odot$), diagrams
comparing the effective temperature ($T_{eff}$) against the small separation
can provide an alternative to Christensen-Dalsgaard (C-D) diagrams. The impact
of the metal abundance of intermediate mass stars (2.5-4.4M$_\odot$) has over
their seismic properties is also evaluated.


title:
The signature of evolving turbulence in quiet solar wind as seen by
  ULYSSES

abstract:
  Solar wind fluctuations, such as magnetic field or velocity, show power law
power spectra suggestive both of an inertial range of intermittent turbulence
(with $\sim -5/3$ exponent) and at lower frequencies, of fluctuations of
coronal origin (with $\sim -1$ exponent). The ULYSSES spacecraft spent many
months in the quiet fast solar wind above the Sun's polar coronal holes in a
highly ordered magnetic field. We use statistical analysis methods such as the
generalized structure function (GSF) and extended self-similarity (ESS) to
quantify the scaling of the moments of the probability density function of
fluctuations in the magnetic field. The GSFs give power law scaling in the
``$f^{-1}$'' range of the form $<| y(t+\tau)-y(t)|^{m}>\sim\tau^{\zeta(m)}$,
but ESS is required to reveal scaling in the inertial range, which is of the
form $<| y(t+\tau)-y(t)|^{m}>\sim [g(\tau)]^{\zeta(m)}$. We find that $g(\tau)$
is independent of spacecraft position and
$g(\tau)\sim\tau^{-log_{10}(\tilde{\lambda}\tau)}$. The ``$f^{-1}$'' scaling
fluctuates with radial spacecraft position. This confirms that, whereas the
``$f^{-1}$'' fluctuations are directly influenced by the corona, the inertial
range fluctuations are consistent with locally evolving turbulence, but with an
``envelope'' $g(\tau)$, which captures the formation of the quiet fast solar
wind.


title:
Semiclassical and Quantum Black Holes and their Evaporation, de Sitter
  and Anti-de Sitter Regimes, Gravitational and String Phase Transitions

abstract:
  An effective string theory in physically relevant cosmological and black hole
space times is reviewed. Explicit computations of the quantum string entropy,
partition function and quantum string emission by black holes (Schwarzschild,
rotating, charged, asymptotically flat, de Sitter dS and AdS space times) in
the framework of effective string theory in curved backgrounds provide an
amount of new quantum gravity results as: (i) gravitational phase transitions
appear with a distinctive universal feature: a square root branch point
singularity in any space time dimensions. This is of the type of the de Vega -
Sanchez transition for the thermal self-gravitating gas of point particles.
(ii) There are no phase transitions in AdS alone. (iii) For $dS$ background,
upper bounds of the Hubble constant H are found, dictated by the quantum string
phase transition.(iv) The Hawking temperature and the Hagedorn temperature are
the same concept but in different (semiclassical and quantum) gravity regimes
respectively. (v) The last stage of black hole evaporation is a microscopic
string state with a finite string critical temperature which decays as usual
quantum strings do in non-thermal pure quantum radiation (no information
loss).(vi) New lower string bounds are given for the Kerr-Newman black hole
angular momentum and charge, which are entirely different from the upper
classical bounds. (vii) Semiclassical gravity states undergo a phase transition
into quantum string states of the same system, these states are duals of each
other in the precise sense of the usual classical-quantum (wave-particle)
duality, which is universal irrespective of any symmetry or isommetry of the
space-time and of the number or the kind of space-time dimensions.


title: Asymptotics for first-passage times of L\'evy processes and random walks

abstract:
  We study the exact asymptotics for the distribution of the first time
$\tau_x$ a L\'evy process $X_t$ crosses a negative level $-x$. We prove that
$\mathbf P(\tau_x>t)\sim V(x)\mathbf P(X_t\ge 0)/t$ as $t\to\infty$ for a
certain function $V(x)$. Using known results for the large deviations of random
walks we obtain asymptotics for $\mathbf P(\tau_x>t)$ explicitly in both light
and heavy tailed cases. We also apply our results to find asymptotics for the
distribution of the busy period in an M/G/1 queue.


title:
NGC 2419: an "intergalactic wanderer" or a simple Galactic Globular
  Cluster?

abstract:
  We have carried out a new photometric study of the remote Galactic globular
cluster NGC 2419, using proprietary and archive B,V,I time-series CCD
photometry of the cluster, that allowed us to discover a large number of new
variable stars and to obtain a new colour magnitude diagram that reaches V ~26
mag over a field of 50X43 square arcmin centered on NGC 2419. The new variables
include 39 RR Lyrae and 11 SX Phoenicis stars. The pulsation properties of the
new RR Lyrae stars confirm and strengthen the classification of NGC 2419 as an
Oosterhoff type II cluster.


title:
Possible agreement of wave function reduction from the basic principles
  of quantum mechanics

abstract:
  Reduction is shown to be a possible consequence of the basic principles of
quantum mechanics, involving no branching of the quantum state of the universe.
The key feature of a measurement is attributed to the creation of macroscopic
germs of ionized tracks, bubbles, sparks and so on, in a superposed quantum
state, the main mechanism being a breaking and a restoration of
``classicality'' in nearby macroscopic objects and their small patterns. A new
significance of quantum probabilities, involving no absolute randomness, is
also proposed.


title: The Neumann problem for singular fully nonlinear operators

abstract:
  We consider the Neumann problem in $C^2$ bounded domains for fully nonlinear
second order operators which are elliptic, homogenous with lower order terms.
Inspired by \cite{bnv}, we define the concept of principal eigenvalue and we
characterize it through the maximum principle. Moreover, Lipschitz regularity,
uniqueness and existence results for solutions of the Neumann problem are
given.


title: Electromagnetic radiation from nuclear collisions at RHIC energies

abstract:
  The hot and dense strongly interacting matter created in collisions of heavy
nuclei at RHIC energies is modeled with relativistic hydrodynamics, and the
spectra of real and virtual photons produced at mid-rapidity in these events
are calculated. Several different sources are considered, and their relative
importance is compared. Specifically, we include jet fragmentation, jet-plasma
interactions, the emission of radiation from the thermal medium and from
primordial hard collisions. Our calculations consistently take into account jet
energy loss, as evaluated in the AMY formalism. We obtain results for the
spectra, the nuclear modification factor (R_AA), and the azimuthal anisotropy
(v_2) that agree with the photon measurements performed by the PHENIX
collaboration at RHIC.


title:
An absorption theorem for minimal AF equivalence relations on Cantor
  sets

abstract:
  We prove that a `small' extension of a minimal AF equivalence relation on a
Cantor set is orbit equivalent to the AF relation. By a `small' extension we
mean an equivalence relation generated by the minimal AF equivalence relation
and another AF equivalence relation which is defined on a closed thin subset.
The result we obtain is a generalization of the main theorem in [GMPS2].


title:
Precision tests of Standard Model with leptonic and semileptonic kaon
  decays

abstract:
  Till the middle of 2004 it appeared that the unitarity relation
Vud^2+Vus^2+Vub^2=1 might not hold at the 2.3sigma level. At that time,
however, Vus was inferred from old experimental data. Since then, a large
experimental and theoretical effort has been invested leading to a removal of
the problem. Thanks to the new and improved measurements by BNL-E865, KLOE,
KTeV, ISTRA+ and NA48, the Kl3 decay rate moved up so that Vus is now
consistent with unitarity. On the theory side, much progress has been made in
order to tame the systematic uncertainties related to the computation of the
Kl3 form factors.
  This joint progress allowed to assess the validity of the CKM unitarity
relation at the level of less than $1%.
  Recent measurements of kaon decays contributing to the determination of
  Vus, Vus/Vud are summarized, and up-to-date evaluations of Vusf0 and Vus are
presented. In addition, we discuss the sensitivity of Kl3 and Kl2 decays to
various scenarios of physics beyond Standard Model.


title: Higgs Structures of Dyonic Instantons

abstract:
  We study Higgs field configurations of dyonic instantons in spontaneously
broken (4+1)-dimensional Yang-Mills theory. The adjoint scalar field solutions
to the covariant Laplace equation in the ADHM instanton background are
constructed in general noncanonical basis, and they are used to study
explicitly the Higgs field configurations of dyonic instantons when the gauge
fields are taken by Jackiw-Nohl-Rebbi instanton solutions. For these solutions
corresponding to small instanton number we then consider in some detail the
zero locus of the Higgs field, which describes the cross section of supertubes
connecting parallel D4-branes in string theory. Also the information on the
Higgs zeroes is used to discuss the residual gauge freedom concerning the
Jackiw-Nohl-Rebbi solutions.


title:
Pressure-induced phase transitions in the multiferroic perovskite BiFeO3
  studied by far-infrared micro-spectroscopy

abstract:
  We present the results of pressure-dependent far-infrared reflectivity
measurements on the multiferroic perovskite BiFeO3 at room temperature. The
observed behavior of the infrared-active phonon modes as a funtion of pressure
clearly reveals two structural phase transitions around 3.0 and 7.5 GPa,
supporting the results of recent Raman and x-ray diffraction studies under
pressure. Based on the pressure-dependent frequency shifts of the
infrared-active phonon modes we discuss the possible character of the phase
transitions.


title:
Structural and conformational dynamics of supercooled polymer melts:
  Insights from first-principles theory and simulations

abstract:
  We report on quantitative comparisons between simulation results of a
bead-spring model and mode-coupling theory calculations for the structural and
conformational dynamics of a supercooled, unentangled polymer melt. We find
semiquantitative agreement between simulation and theory, except for processes
that occur on intermediate length scales between the compressibility plateau
and the amorphous halo of the static structure factor. Our results suggest that
the onset of slow relaxation in a glass-forming melt can be described in terms
of monomer-caging supplemented by chain connectivity. Furthermore, a unified
atomistic description of glassy arrest and of conformational fluctuations that
(asymptotically) follow the Rouse model, emerges from our theory.


title: On the minimum mass of reionization sources

abstract:
  By means of carefully calibrated semi-analytical reionization models, we
estimate the minimum mass of star-forming haloes required to match the current
data. Models which do not include haloes of total mass M < 10^9 M_sun fail at
reproducing the Gunn-Peterson and electron scattering optical depths
simultaneously, as they contribute too few (many) photons at high (low, z
\approx 6) redshift. Marginally acceptable solutions require haloes with M
\approx 5 \times 10^7 M_sun at z \approx 10, corresponding to virial
temperatures (\sim 10^4K) for which cooling can be ensured by atomic
transitions. However, a much better match to the data is obtained if minihaloes
(M \sim 10^6 M_sun) are included in the analysis. We have critically examined
the assumptions made in our model and conclude that reionization in the
large-galaxies-only scenario can remain viable only if metal-free stars and/or
some other exotic sources at z > 6 are included.


title:
A new period determination for the close PG1159 binary
  SDSSJ212531.92-010745.9

abstract:
  Methods to measure masses of PG1159 stars in order to test evolutionary
scenarios are currently based on spectroscopic masses or asteroseismological
mass determinations. One recently discovered PG1159 star in a close binary
system may finally allow the first dynamical mass determination, which has so
far been analysed on the basis of one SDSS spectrum and photometric monitoring.
  In order to be able to phase future radial velocity measurements of the
system SDSSJ212531.92-010745.9, we follow up on the photometric monitoring of
this system to provide a solid observational basis for an improved orbital
ephemeris determination.
  New white-light time series of the brightness variation of
SDSSJ212531.92-010745.9 with the Tuebingen 80cm and Goettingen 50cm telescopes
extend the monitoring into a second season (2006), tripling the length of
overall observational data available, and significantly increasing the time
base covered.
  We give the ephemeris for the orbital motion of the system, based on a sine
fit which now results in a period of 6.95573(5)h, and discuss the associated
new amplitude determination in the context of the phased light curve variation
profile. The accuracy of the ephemeris has been improved by more than one order
of magnitude compared to that previously published for 2005 alone.


title:
Phase noise measurements in long fiber interferometers for quantum
  repeaters applications

abstract:
  Many protocols for long distance quantum communication require
interferometric phase stability over long distances of optical fibers. In this
paper we investigate the phase noise in long optical fibers both in laboratory
environment and in installed commercial fibers in an urban environment over
short time scales (up to hundreds of us). We show that the phase fluctuations
during the travel time of optical pulses in long fiber loops are small enough
to obtain high visibility first order interference fringes in a Sagnac
interferometer configuration for fiber lengths up to 75 km. We also measure
phase fluctuations in a Mach-Zehnder interferometer in installed fibers with
arm length 36.5 km. We verify that the phase noise respects gaussian
distribution and measure the mean phase change as a function of time
difference. The typical time needed for a mean phase change of 0.1 rad is of
order of 100 us, which provides information about the time scale available for
active phase stabilization. Our results are relevant for future implementations
of quantum repeaters in installed optical fiber networks.


title:
Analysis of broadband microwave conductivity and permittivity
  measurements of semiconducting materials

abstract:
  We perform broadband phase sensitive measurements of the reflection
coefficient from 45 MHz up to 20 GHz employing a vector network analyzer with a
2.4 mm coaxial sensor which is terminated by the sample under test. While the
material parameters (conductivity and permittivity) can be easily extracted
from the obtained impedance data if the sample is metallic, no direct solution
is possible if the material under investigation is an insulator. Focusing on
doped semiconductors with largely varying conductivity, here we present a
closed calibration and evaluation procedure for frequencies up to 5 GHz, based
on the rigorous solution for the electromagnetic field distribution inside the
sample combined with the variational principle; basically no limiting
assumptions are necessary. A simple static model based on the electric current
distribution proves to yield the same frequency dependence of the complex
conductivity up to 1 GHz. After a critical discussion we apply the developed
method to the hopping transport in Si:P at temperature down to 1 K.


title:
New Light Curves and Spectra of the close PG1159 Binary System
  SDSSJ212531.92-010745.9

abstract:
  Methods to measure masses of PG1159 stars in order to test evolutionary
scenarios are currently based on spectroscopic masses or asteroseismological
mass determinations. SDSSJ212531.92-010745.9, a recently discovered PG1159 star
in a close binary system, may finally allow the first dynamical mass
determination, and has so far been analysed on the basis of one SDSS spectrum
and photometric monitoring.
  In order to be able to phase radial velocity measurements of the system
SDSSJ212531.92-010745.9, we have followed up the photometric monitoring of this
system. New white light time series of the brightness variation of
SDSSJ212531.92-010745.9 with the Tuebingen 80cm and Goettingen 50cm telescopes
extend the monitoring into a second season (2006). We give the improved
ephemeris for the orbital motion of the system, based on a sine fit which now
results in a period of 6.95573(5)h.
  In 2007, we have obtained a series of phase-resolved medium-resolution
spectra with the TWIN spectrograph at the 3.5m telescope at Calar Alto, which
will allow us to derive the radial velocity curves for both components of the
system, and to perform spectral analyses of the irradiating and irradiated
components at different phases. We briefly describe the newly obtained spectra.
The light curve and radial velocities combined will allow us to carry out a
mass determination.


title:
Effect of curvature squared corrections in AdS on the viscosity of the
  dual gauge theory

abstract:
  We use the real-time finite-temperature AdS/CFT correspondence to compute the
effect of general R^2 corrections to the gravitational action in AdS space on
the shear viscosity of the dual gauge theory. The R^2 terms in AdS_5 are
determined by the central charges of the CFT. We present an example of a
four-dimensional gauge theory in which the conjectured lower bound of 1/(4\pi)
on the viscosity-to-entropy ratio is violated for finite N.


title: Computational Chemotaxis in Ants and Bacteria over Dynamic Environments

abstract:
  Chemotaxis can be defined as an innate behavioural response by an organism to
a directional stimulus, in which bacteria, and other single-cell or
multicellular organisms direct their movements according to certain chemicals
in their environment. This is important for bacteria to find food (e.g.,
glucose) by swimming towards the highest concentration of food molecules, or to
flee from poisons. Based on self-organized computational approaches and similar
stigmergic concepts we derive a novel swarm intelligent algorithm. What strikes
from these observations is that both eusocial insects as ant colonies and
bacteria have similar natural mechanisms based on stigmergy in order to emerge
coherent and sophisticated patterns of global collective behaviour. Keeping in
mind the above characteristics we will present a simple model to tackle the
collective adaptation of a social swarm based on real ant colony behaviors (SSA
algorithm) for tracking extrema in dynamic environments and highly multimodal
complex functions described in the well-know De Jong test suite. Later, for the
purpose of comparison, a recent model of artificial bacterial foraging (BFOA
algorithm) based on similar stigmergic features is described and analyzed.
Final results indicate that the SSA collective intelligence is able to cope and
quickly adapt to unforeseen situations even when over the same cooperative
foraging period, the community is requested to deal with two different and
contradictory purposes, while outperforming BFOA in adaptive speed. Results
indicate that the present approach deals well in severe Dynamic Optimization
problems.


title: Neutron reflection from the surface of normal and superfluid 4He

abstract:
  The reflection of neutrons from a helium surface has been observed for the
first time. The 4He surface is smoother in the superfluid state at 1.54 K than
in the case of the normal liquid at 2.3 K. In the superfluid state we also
observe a surface layer ~200 Angstroms thick which has a subtly different
neutron scattering cross-section, which may be explained by an enhanced
Bose-Einstein condensate fraction close to the helium surface.


title: Testing BFKL evolution with Mueller-Navelet jets

abstract:
  We study the correlation in azimuthal angle between Mueller-Navelet jets
produced in hadron-hadron collisions. We argue that this observable would test
the BFKL approach at next-to-leading logarithmic accuracy. In order to motivate
such a measurement, we give predictions for jets separated by large rapidity
intervals within the Tevatron and LHC ranges.


title: Spinor-Vector Duality in N=2 Heterotic String Vacua

abstract:
  Classification of the N=1 space-time supersymmetric fermionic Z2XZ2
heterotic-string vacua with symmetric internal shifts, revealed a novel
spinor-vector duality symmetry over the entire space of vacua, where the S_t
<-> V duality interchanges the spinor plus anti-spinor representations with
vector representations. In this paper we demonstrate that the spinor--vector
duality exists also in fermionic Z2 heterotic string models, which preserve N=2
space-time supersymmetry. In this case the interchange is between spinorial and
vectorial representations of the unbroken SO(12) GUT symmetry. We provide a
general algebraic proof for the existence of the S_t <-> V duality map. We
present a novel basis to generate the free fermionic models in which the ten
dimensional gauge degrees of freedom are grouped into four groups of four, each
generating an SO(8) modular block. In the new basis the GUT symmetries are
produced by generators arising from the trivial and non--trivial sectors, and
due to the triality property of the SO(8) representations. Thus, while in the
new basis the appearance of GUT symmetries is more cumbersome, it may be more
instrumental in revealing the duality symmetries that underly the string vacua.


title:
Understanding the nucleation mechanisms of Carbon Nanotubes in catalytic
  Chemical Vapor Deposition

abstract:
  The nucleation of carbon caps on small nickel clusters is studied using a
tight binding model coupled to grand canonical Monte Carlo simulations. It
takes place in a well defined carbon chemical potential range, when a critical
concentration of surface carbon atoms is reached. The solubility of carbon in
the outermost Ni layers, that depends on the initial, crystalline or
disordered, state of the catalyst and on the thermodynamic conditions, is
therefore a key quantity to control the nucleation.


title:
Instabilities at vicinal crystal surfaces - competition between the
  electromigration of the adatoms and the kinetic memory effect

abstract:
  We studied the step dynamics during sublimation and growth in the presence of
electromigration force acting on the adatoms. In the limit of fast surface
diffusion and slow kinetics of atom attachment-detachment at the steps we
formulate a model free of the quasi-static approximation in the calculation of
the adatom concentration on the terraces. Numerical integration of the
equations for the time evolution of the adatom concentrations and the equations
of step motion reveals two different step bunching instabilities: 1) step
density waves (small bunches which do not manifest any coarsening) induced by
the kinetic memory effect and 2) step bunching with coarsening when the
dynamics is dominated by the electromigration. The model developed in this
paper also provides very instructive illustrations of the Popkov-Krug dynamical
phase transition during sublimation and growth of a vicinal crystal surface.


title: Vibration-induced correction to the current through a single molecule

abstract:
  We provide analytical results for the perturbative correction to the
current-voltage relation through a vibrating molecule for weak electron-phonon
coupling. The nonlinear conductance exhibits a step-like feature at $eV=\hbar
\omega_0$, where $\omega_0$ is the vibration frequency. We establish criteria
for the sign change of the step in the conductance (up or down). This
transition turns out to be nonuniversal and is governed by essentially all
system parameters.


title: Melting of alloys along grain boundaries

abstract:
  We discuss melting of alloys along grain boundaries as a free boundary
problem for two moving solid-liquid interfaces. One of them is the melting
front and the other is the solidification front. The presence of the triple
junction plays an important role in controlling the velocity of this process.
The interfaces strongly interact via the diffusion field in the thin liquid
layer between them. In the liquid film migration (LFM) mechanism the system
chooses a more efficient kinetic path, which is controlled by diffusion in the
liquid film on relatively short distances. However, only weak coherency strain
energy is the effective driving force for LFM in the case of melting of
one-phase alloys.
  The process with only one melting front would be controlled by the very slow
diffusion in the mother solid phase on relatively large distances.


title: A Mathematical Justification for the Herman-Kluk Propagator

abstract:
  A class of Fourier Integral Operators which converge to the unitary group of
the Schroedinger equation in semiclassical limit $\eps\to 0$ is constructed.
The convergence is in the uniform operator norm and allows for an error bound
of order $O(\eps^{1-\rho})$ for Ehrenfest timescales, where $\rho$ can be made
arbitrary small. For the shorter times of order O(1), the error can be improved
to arbitrary order in $\eps$. In the chemical literature the approximation is
known as the Herman-Kluk propagator.


title:
Surface dissipation in nanoelectromechanical systems: Unified
  description with the standard tunneling model and effects of metallic
  electrodes

abstract:
  By modifying and extending recent ideas [C. Seoanez et al., Europhys. Lett.
78, 60002 (2007)], a theoretical framework to describe dissipation processes in
the surfaces of vibrating micro- and nanoelectromechanical devices, thought to
be the main source of friction at low temperatures, is presented. Quality
factors as well as frequency shifts of flexural and torsional modes in doubly
clamped beams and cantilevers are given, showing the scaling with dimensions,
temperature, and other relevant parameters of these systems. Full agreement
with experimental observations is not obtained, leading to a discussion of
limitations and possible modifications of the scheme to reach a quantitative
fitting to experiments. For nanoelectromechanical systems covered with metallic
electrodes, the friction due to electrostatic interaction between the flowing
electrons and static charges in the device and substrate is also studied.


title:
Asymptotic analysis of vibrating system containing stiff-heavy and
  flexible-light parts

abstract:
  A model of strongly inhomogeneous medium with simultaneous perturbation of
rigidity and mass density is studied. The medium has strongly contrasting
physical characteristics in two parts with the ratio of rigidities being
proportional to a small parameter $\epsilon$. Additionally, the ratio of mass
densities is of order $\epsilon^{-1}$. We investigate the asymptotic behaviour
of spectrum and eigensubspaces as $\epsilon\to 0$. Complete asymptotic
expansions of eigenvalues and eigenfunctions are constructed and justified.
  We show that the limit operator is nonself-adjoint in general and possesses
two-dimensional Jordan cells in spite of the singular perturbed problem is
associated with a self-adjoint operator in appropriated Hilbert space
$L_\epsilon$. This may happen if the metric in which the problem is
self-adjoint depends on small parameter $\epsilon$ in a singular way. In
particular, it leads to a loss of completeness for the eigenfunction
collection. We describe how root spaces of the limit operator approximate
eigenspaces of the perturbed operator.


title: GALEX Ultraviolet photometry of NGC 2420: searching for WDs

abstract:
  We present color-magnitude diagrams of the open cluster NGC 2420, obtained
from Galaxy Evolution Explorer (GALEX) ultraviolet images in FUV and NUV bands
and Sloan Digital Sky Survey (SDSS) u,g,r,i,z photometry. Our goal is to search
for and characterize hot evolved stars and peculiar objects in this open
cluster, as part of a larger project aimed to study a number of open clusters
in the Milky Way with GALEX and ground-based data.


title: Modeling X-ray Loops and EUV "Moss" in an Active Region Core

abstract:
  The Soft X-ray intensity of loops in active region cores and corresponding
footpoint, or moss, intensity observed in the EUV remain steady for several
hours of observation. The steadiness of the emission has prompted many to
suggest that the heating in these loops must also be steady, though no direct
comparison between the observed X-ray and EUV intensities and the steady
heating solutions of the hydrodynamic equations has yet been made. In this
paper, we perform these simulations and simultaneously model the X-Ray and EUV
moss intensities in one active regioncore with steady uniform heating. To
perform this task, we introduce a new technique to constrain the model
parameters using the measured EUV footpoint intensity to infer a heating rate.
We find that a filling factor of 8% and loops that expand with height provides
the best agreement with the intensity in two X-ray filters, though the
simulated SXT Al12 intensity is 147% the observed intensity and the SXT AlMg
intensity is 80% the observed intensity. From this solution, we determine the
required heating rate scales as ${\bar{B}}^{0.29} L^{-0.95}$. Finally we
discuss the future potential of this type of modeling, such as the ability to
use density measurements to fully constrain filling factor, and its
shortcomings, such as the requirement to use potential field extrapolations to
approximate the coronal field.


title:
Transport through a double quantum dot system with non-collinearly
  polarized leads

abstract:
  We investigate linear and non-linear transport in a double quantum dot system
weakly coupled to spin-polarized leads.
  In the linear regime, the conductance as well as the non-equilibrium spin
accumulation are evaluated in analytic form. The conductance as a function of
the gate voltage exhibits four peaks of different height, with mirror symmetry
with respect to the charge neutrality point. As the polarization angle is
varied, the position and shape of the peaks changes in a characteristic way
which preserves the electron-hole symmetry of the problem. In the nonlinear
regime negative differential conductance features occur for non collinear
magnetisations of the leads. In the considered sequential tunneling limit, the
tunneling magneto resistance (TMR) is always positive with a characteristic
gate voltage dependence for non-collinear magnetization. If a magnetic field is
added to the system, the TMR can become negative.


title:
Two Circular-Rotational Eigenmodes in Vortex Gyrotropic Motions in Soft
  Magnetic Nanodots

abstract:
  We found, by micromagnetic numerical and analytical calculations, that the
clockwise (CW) and counterclockwise (CCW) circular-rotational motions of a
magnetic vortex core in a soft magnetic circular nanodot are the elementary
eigenmodes existing in the gyrotropic motion with respect to the corresponding
CW and CCW circular-rotational-field eigenbasis. Any steady-state vortex
gyrotropic motions driven by a linearly polarized oscillating in-plane magnetic
field in the linear regime can be perfectly understood according to the
superposition of the two circular eigenmodes, which show asymmetric resonance
characteristics reflecting the vortex polarization. The relative magnitudes in
the amplitude and phase between the CCW and CW eigenmodes determine the
elongation and orientation of the orbital trajectories of the vortex core
motions, respectively, which trajectories vary with the polarization and
chirality of the given vortex as well as the field frequency across the
resonance frequency.


title: Quantum light depolarization: the phase-space perspective

abstract:
  Quantum light depolarization is handled through a master equation obtained by
coupling dispersively the field to a randomly distributed atomic reservoir.
This master equation is solved by transforming it into a quasiprobability
distribution in phase space and the quasiclassical limit is investigated.


title:
Electron transport in the four-lead two-impurity Kondo model:
  Nonequilibrium perturbation theory with almost degenerate levels

abstract:
  The eigenstates of an isolated nanostructure may get mixed by the coupling to
external leads. This effect is the stronger, the smaller the level splitting on
the dot and the larger the broadening induced by the coupling to the leads. We
describe how to calculate the nondiagonal density matrix of the nanostructure
efficiently in the cotunneling regime. As an example, we consider a system of
two quantum dots in the Kondo regime, the two spins coupled by an
antiferromagnetic exchange interaction and each dot tunnel coupled to two
leads. Calculating the nonequilibrium density matrix and the corresponding
current, we demonstrate the importance of the off-diagonal terms in the
presence of an applied magnetic field and a finite bias voltage.


title:
Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected
  in the Optical Transmission Spectrum

abstract:
  We present the first ground-based detection of sodium absorption in the
transmission spectrum of an extrasolar planet. Absorption due to the atmosphere
of the extrasolar planet HD189733b is detected in both lines of the NaI
doublet. High spectral resolution observations were taken of eleven transits
with the High Resolution Spectrograph (HRS) on the 9.2 meter Hobby-Eberly
Telescope (HET). The NaI absorption in the transmission spectrum due to
HD189733b is (-67.2 +/- 20.7) x 10^-5 deeper in the ``narrow'' spectral band
that encompasses both lines relative to adjacent bands. The 1-sigma error
includes both random and systematic errors, and the detection is >3-sigma. This
amount of relative absorption in NaI for HD189733b is ~3x larger than detected
for HD209458b by Charbonneau et al. (2002), and indicates these two
hot-Jupiters may have significantly different atmospheric properties.


title:
Probing FSR star cluster candidates in bulge/disk directions with 2MASS
  colour-magnitude diagrams

abstract:
  We analyse 20 star cluster candidates projected mostly in the bulge direction
($|\ell|<60^\circ$). The sample contains all candidates in that sector
classified by \citet{FSRcat} with quality flags denoting high probability of
being star clusters. Bulge contamination in the colour-magnitude diagrams
(CMDs) is in general important, while at lower Galactic latitudes disk stars
contribute as well. Properties of the candidates are investigated with 2MASS
CMDs and stellar radial density profiles (RDPs) built with field star
decontaminated photometry. To uncover the nature of the structures we
decontaminate the CMDs from field stars using tools that we previously
developed to deal with objects in dense fields. We confirm in all cases
excesses in the RDPs with respect to the background level, as expected from the
method the candidates were originally selected. CMDs and RDPs taken together
revealed 6 open clusters, 5 uncertain cases that require deeper observations,
while 9 objects are possibly field density fluctuations.


title: Light-induced rotation of dye-doped liquid crystal droplets

abstract:
  We investigate both theoretically and experimentally the rotational dynamics
of micrometric droplets of dye-doped and pure liquid crystal induced by
circularly and elliptically polarized laser light. The droplets are dispersed
in water and trapped in the focus of the laser beam. Since the optical torque
acting on the molecular director is known to be strongly enhanced in
light-absorbing dye-doped materials, the question arises whether a similar
enhancement takes place also for the overall optical torque acting on the whole
droplets. We searched for such enhancement by measuring and comparing the
rotation speed of dye-doped droplets induced by a laser beam having a
wavelength either inside or outside the dye absorption band, and also comparing
it with the rotation of pure liquid crystal droplets. No enhancement was found,
confirming that photoinduced dye effects are only associated with an internal
exchange of angular momentum between orientational and translational degrees of
freedom of matter. Our result provides also the first direct experimental proof
of the existence of a photoinduced stress tensor in the illuminated dye-doped
liquid crystal. Finally, peculiar photoinduced dynamical effects are predicted
to occur in droplets in which the molecular director is not rigidly locked to
the flow, but so far they could not be observed.


title: The Conception of Atom in Greek and Indian Physics

abstract:
  This paper contrasts the Greek and Indian conceptions of atom. It is shown
that these two are quite different in spirit.


title: Remarks on the tight-binding model of graphene

abstract:
  We address a simple but fundamental issue arising in the study of graphene,
as well as of other systems that have a crystalline structure with more than
one atom per unit cell. For these systems, the choice of the tight-binding
basis is not unique. For monolayer graphene two bases are widely used in the
literature. While the expectation values of operators describing physical
quantities should be independent of basis, the form of the operators may depend
on the basis, especially in the presence of disorder or of an applied magnetic
field. Using the inappropriate form of certain operators may lead to erroneous
physical predictions. We discuss the two bases used to describe monolayer
graphene, as well as the form of the most commonly used operators in the two
bases. We repeat our analysis for the case of bilayer graphene.


title: Dust evolution in protoplanetary disks

abstract:
  We investigate the behaviour of dust in protoplanetary disks under the action
of gas drag using our 3D, two-fluid (gas+dust) SPH code. We present the
evolution of the dust spatial distribution in global simulations of planetless
disks as well as of disks containing an already formed planet. The resulting
dust structures vary strongly with particle size and planetary gaps are much
sharper than in the gas phase, making them easier to detect with ALMA than
anticipated. We also find that there is a range of masses where a planet can
open a gap in the dust layer whereas it doesn't in the gas disk. Our dust
distributions are fed to the radiative transfer code MCFOST to compute
synthetic images, in order to derive constraints on the settling and growth of
dust grains in observed disks.


title: Surface-mediated non-linear optical effects in liquid crystals

abstract:
  We make a phenomenological model of optical two-beam interaction in a model
planar liquid crystal cell. The liquid crystal is subject to homeotropic
anchoring at the cell walls, is surrounded by thin photosensitive layers, and
is subject to a variable potential across the cell. These systems are often
known as liquid crystal photorefractive systems. The interference between the
two obliquely incident beams causes a time-independent periodic modulation in
electric field intensity in the direction transverse to the cell normal. Our
model includes this field phenomenologically by affecting the potential at the
walls of the cell. The transverse periodic surface potential causes spatially
periodic departures from a pure homeotropic texture. The texture modulation
acts as a grating for the incident light. The incident light is both directly
transmitted and also subject to diffraction. The first diffracted beams result
in energy exchange between the beams. We find that the degree of energy
exchange can be strongly sensitive to the mean angle of incidence, the angle
between the beams, and the imposed potential across the cell. We use the model
to speculate about what factors optimize non-linear optical interaction in
liquid crystalline photorefractive systems.


title: Strange quark mass from Finite Energy QCD sum rules to five loops

abstract:
  The strange quark mass is determined from a new QCD Finite Energy Sum Rule
(FESR) optimized to reduce considerably the systematic uncertainties arising
from the hadronic resonance sector. As a result, the main uncertainty in this
determination is due to the value of $\Lambda_{QCD}$. The correlator of
axial-vector divergences is used in perturbative QCD to five-loop order,
including quark and gluon condensate contributions, in the framework of both
Fixed Order (FOPT), and Contour Improved Perturbation Theory (CIPT). The latter
exhibits very good convergence, leading to a remarkably stable result in the
very wide range $s_0 = 1.0 - 4.0 {GeV}^2$, where $s_0$ is the radius of the
integration contour in the complex energy (squared) plane. The value of the
strange quark mass in this framework at a scale of 2 GeV is $m_s(2 {GeV}) = 95
\pm 5 (111 \pm 6) {MeV}$ for $\Lambda_{QCD} = 420
  (330) {MeV}$, respectively.


title:
Towards 3D ultrasound image based soft tissue tracking: a transrectal
  ultrasound prostate image alignment system

abstract:
  The emergence of real-time 3D ultrasound (US) makes it possible to consider
image-based tracking of subcutaneous soft tissue targets for computer guided
diagnosis and therapy. We propose a 3D transrectal US based tracking system for
precise prostate biopsy sample localisation. The aim is to improve sample
distribution, to enable targeting of unsampled regions for repeated biopsies,
and to make post-interventional quality controls possible. Since the patient is
not immobilized, since the prostate is mobile and due to the fact that probe
movements are only constrained by the rectum during biopsy acquisition, the
tracking system must be able to estimate rigid transformations that are beyond
the capture range of common image similarity measures. We propose a fast and
robust multi-resolution attribute-vector registration approach that combines
global and local optimization methods to solve this problem. Global
optimization is performed on a probe movement model that reduces the
dimensionality of the search space and thus renders optimization efficient. The
method was tested on 237 prostate volumes acquired from 14 different patients
for 3D to 3D and 3D to orthogonal 2D slices registration. The 3D-3D version of
the algorithm converged correctly in 96.7% of all cases in 6.5s with an
accuracy of 1.41mm (r.m.s.) and 3.84mm (max). The 3D to slices method yielded a
success rate of 88.9% in 2.3s with an accuracy of 1.37mm (r.m.s.) and 4.3mm
(max).


title: About the stability of the tangent bundle restricted to a curve

abstract:
  Let C be a smooth projective curve with genus g>1 and Clifford index c(C) and
let L be a line bundle on C generated by its global sections. The morphism i:C
-->P(H^0(L))=P is well-defined and i*T is the restriction to C of the tangent
bundle T of the projective space P. Sharpening a theorem by Paranjape, we show
that if deg L>2g-c(C)-1 then i*T is semi-stable, specifying when it is also
stable. We then prove the existence on many curves of a line bundle L of degree
2g-c(C)-1 such that i*T is not semi-stable. Finally, we completely characterize
the (semi-)stability of i*T when C is hyperelliptic.


title:
Magnetic, Chemical and Rotational Properties of the Herbig Ae/Be Binary
  System HD 72106

abstract:
  Recently, strong, globally-ordered magnetic fields have been detected in some
Herbig Ae and Be (HAeBe) stars, suggesting a possible evolutionary connection
to main sequence magnetic chemically peculiar Ap and Bp stars. We have
undertaken a detailed study of the binary system HD 72106, which contains a B9
magnetic primary and a HAeBe secondary, using the ESPaDOnS spectropolarimeter
mounted on the CFHT. A careful analysis of the very young primary reveals that
it has an approximately dipolar magnetic field geometry, strong chemical
peculiarities, and strong surface chemical abundance inhomogeneities. Thus the
primary is very similar to an Ap/Bp star despite having completed less then
1.5% of its main sequence life, and possibly still being on the pre-main
sequence. In contrast, a similar analysis of the secondary reveals solar
chemical abundances and no magnetic field.


title: 3D SPH simulations of grain growth in protoplanetary disks

abstract:
  We present the first results of the treatment of grain growth in our 3D,
two-fluid (gas+dust) SPH code describing protoplanetary disks. We implement a
scheme able to reproduce the variation of grain sizes caused by a variety of
physical processes and test it with the analytical expression of grain growth
given by Stepinski & Valageas (1997) in simulations of a typical T Tauri disk
around a one solar mass star. The results are in agreement with a turbulent
growing process and validate the method. We are now able to simulate the grain
growth process in a protoplanetary disk given by a more realistic physical
description, currently under development. We discuss the implications of the
combined effect of grain growth and dust vertical settling and radial migration
on subsequent planetesimal formation.


title: Influence of Absorbers on the Electromagnetic Radiation

abstract:
  The phenomenon of the electromagnetic absorption by arbitrarily distributed
discrete absorbers is analyzed from the photon point of view. It is shown that
apart from the decrease in the intensity of the signal the net effect of
absorption includes a relative increase in the photon bunching.


title: Four Zero Neutrino Yukawa Textures in the Minimal Seesaw Framework

abstract:
  We investigate, within the Type I seesaw framework, the physical implications
of zero textures in the Yukawa couplings which generate the neutrino Dirac mass
matrix $m_D$. It is shown that four is the maximal number of texture zeroes
compatible with the observed leptonic mixing and the assumption that no
neutrino mass vanishes. We classify all allowed four-zero textures of $m_D$
into two categories with three classes each. We show that the different
classes, in general, admit CP violation both at low and high energies. We
further present the constraints obtained for low energy physics in each case.
The r\^ ole of these zero textures in establishing a connection between
leptogenesis and low energy data is analysed in detail. It is shown that it is
possible in all cases to completely specify the parameters relevant for
leptogenesis in terms of light neutrino masses and leptonic mixing together
with the unknown heavy neutrino masses.


title:
Some nonasymptotic results on resampling in high dimension, I:
  Confidence regions, II: Multiple tests

abstract:
  We study generalized bootstrap confidence regions for the mean of a random
vector whose coordinates have an unknown dependency structure. The random
vector is supposed to be either Gaussian or to have a symmetric and bounded
distribution. The dimensionality of the vector can possibly be much larger than
the number of observations and we focus on a nonasymptotic control of the
confidence level, following ideas inspired by recent results in learning
theory. We consider two approaches, the first based on a concentration
principle (valid for a large class of resampling weights) and the second on a
resampled quantile, specifically using Rademacher weights. Several intermediate
results established in the approach based on concentration principles are of
interest in their own right. We also discuss the question of accuracy when
using Monte Carlo approximations of the resampled quantities.


title:
Identification of RR Lyrae Variables in SDSS from Single-Epoch
  Photometric and Spectroscopic Observations

abstract:
  We describe a new RR Lyrae identification technique based on out-of-phase
single-epoch photometric and spectroscopic observations contained in SDSS Data
Release 6 (DR-6). This technique detects variability by exploiting the large
disparity between the g-r color and the strength of the hydrogen Balmer lines
when the two observations are made at random phases. Comparison with a large
sample of known variables in the SDSS equatorial stripe (Stripe 82) shows that
the discovery efficiency for our technique is ~85%. Analysis of stars with
multiple spectroscopic observations suggests a similar efficiency throughout
the entire DR-6 sample. We also develop a technique to estimate the average g
apparent magnitude (over the pulsation cycle) for individual RR Lyrae stars,
using the <g-r> for the entire sample and measured colors for each star. The
resulting distances are found to have precisions of ~14%. Finally, we explore
the properties of our DR-6 sample of N = 1087 variables, and recover portions
of the Sagittarius Northern and Southern Stream. Analysis of the distance and
velocity for the Southern Stream are consistent with previously published data
for blue horizontal-branch stars. In a sample near the North Galactic Polar
Cap, we find evidence for the descending leading Northern arm, and a possible
detection of the trailing arm.


title: T-odd effects in photon-jet production at the Tevatron

abstract:
  The angular distribution in photon-jet production in p \bar{p} -> \gamma jet
X is studied within a generalized factorization scheme taking into account the
transverse momentum of the partons in the initial hadrons. Within this scheme
an anomalously large cos(2\phi) asymmetry observed in the Drell-Yan process
could be attributed to the T-odd, spin and transverse momentum dependent parton
distribution function h_1^{\perp q}(x, p_{\perp}^2). This same function is
expected to produce a cos(2\phi) asymmetry in the photon-jet production cross
section. We give the expression for this particular azimuthal asymmetry, which
is estimated to be smaller than the Drell-Yan asymmetry but still of
considerable size for Tevatron kinematics. This offers a new possibility to
study T-odd effects at the Tevatron.


title:
A Nearly Scale Invariant Spectrum of Gravitational Radiation from Global
  Phase Transitions

abstract:
  Using a large N sigma model approximation we explicitly calculate the power
spectrum of gravitational waves arising from a global phase transition in the
early universe and we confirm that it is scale invariant, implying an
observation of such a spectrum may not be a unique feature of inflation.
Moreover, the predicted amplitude can be over 3 orders of magnitude larger than
the naive dimensional estimate, implying that even a transition that occurs
after inflation may dominate in Cosmic Microwave Background polarization or
other gravity wave signals.


title: Frequency-dependent fluctuation-dissipation relations in granular gases

abstract:
  The Green-Kubo relation for two models of granular gases is discussed. In the
Maxwell model in any dimension, the effective temperature obtained from the
Green-Kubo relation is shown to be frequency independent, and equal to the
average kinetic energy, known as the granular temperature. In the second model
analyzed, a mean-field granular gas, the collision rate of a particle is taken
to be proportional to its velocity. The Green-Kubo relation in the high
frequency limit is calculated for this model, and the effective temperature in
this limit is shown to be equal to the granular temperature. This result, taken
together with previous results, showing a difference between the effective
temperature at zero frequency (the Einstein relation) and the granular
temperature, shows that the Green-Kubo relation for granular gases is violated.


title: Infrared finite ghost propagator in the Feynman gauge

abstract:
  We demonstrate how to obtain from the Schwinger-Dyson equations of QCD an
infrared finite ghost propagator in the Feynman gauge. The key ingredient in
this construction is the longitudinal form factor of the non-perturbative
gluon-ghost vertex, which, contrary to what happens in the Landau gauge,
contributes non-trivially to the gap equation of the ghost. The detailed study
of the corresponding vertex equation reveals that in the presence of a
dynamical infrared cutoff this form factor remains finite in the limit of
vanishing ghost momentum. This, in turn, allows the ghost self-energy to reach
a finite value in the infrared, without having to assume any additional
properties for the gluon-ghost vertex, such as the presence of massless poles.
The implications of this result and possible future directions are briefly
outlined.


title: The flavor problem and discrete symmetries

abstract:
  In this letter we propose a multi-Higgs extension of the standard model with
Abelian and non-Abelian discrete symmetries in which the mass matrices of the
charged fermions obtained from renormalizable interactions are diagonal.
Corrections induced by non-renormalizable interactions deviate these matrices
from the diagonal form. Active neutrinos acquire mass only from
non-renormalizable interactions. The main entries of the neutrino mass matrix
arise only through dimension five operators, while the diagonal entries arise
only from dimension six operators.


title: Hypergeometric-Gaussian Modes

abstract:
  We studied a novel family of paraxial laser beams forming an overcomplete yet
nonorthogonal set of modes. These modes have a singular phase profile and are
eigenfunctions of the photon orbital angular momentum. The intensity profile is
characterized by a single brilliant ring with the singularity at its center,
where the field amplitude vanishes. The complex amplitude is proportional to
the degenerate (confluent) hypergeometric function, and therefore we term such
beams hypergeometric gaussian (HyGG) modes. Unlike the recently introduced
hypergeometric modes (Opt. Lett. {\textbf 32}, 742 (2007)), the HyGG modes
carry a finite power and have been generated in this work with a liquid-crystal
spatial light modulator. We briefly consider some sub-families of the HyGG
modes as the modified Bessel Gaussian modes, the modified exponential Gaussian
modes and the modified Laguerre-Gaussian modes.


title:
Trouble for AGN Feedback ? The puzzle of the core of the Galaxy Cluster
  AWM 4

abstract:
  The core of the relaxed cluster AWM 4 is characterized by a unique
combination of properties which defy a popular scenario for ANG heating of
cluster cores. A flat inner temperature profile is indicative of a past, major
heating episode which completely erased the cool core, as testified by the high
central cooling time (~ 3 Gyr) and by the high central entropy level (~ 60 keV
cm^2). Yet the presence of a 1.4 GHz active central radio galaxy with extended
radio lobes out to 100 kpc, reveals recent feeding of the central massive black
hole. A system like AWM 4 should have no radio emission at all if only feedback
from the cooling hot gas regulates the AGN activity.


title: Model for erosion-deposition patterns

abstract:
  We investigate through computational simulations with a pore network model
the formation of patterns caused by erosion-deposition mechanisms. In this
model, the geometry of the pore space changes dynamically as a consequence of
the coupling between the fluid flow and the movement of particles due to local
drag forces. Our results for this irreversible process show that the model is
capable to reproduce typical natural patterns caused by well known erosion
processes. Moreover, we observe that, within a certain range of porosity
values, the grains form clusters that are tilted with respect to the horizontal
with a characteristic angle. We compare our results to recent experiments for
granular material in flowing water and show that they present a satisfactory
agreement.


title:
Linear Complete Differential Resultants and the Implicitization of
  Linear DPPEs

abstract:
  The linear complete differential resultant of a finite set of linear ordinary
differential polynomials is defined. We study the computation by linear
complete differential resultants of the implicit equation of a system of $n$
linear differential polynomial parametric equations in $n-1$ differential
parameters. We give necessary conditions to ensure properness of the system of
differential polynomial parametric equations.


title: Hausdorff hyperspaces of $R^m$ and their dense subspaces

abstract:
  Let $CLB_H(X)$ denote the hyperspace of closed bounded subsets of a metric
space $X$, endowed with the Hausdorff metric topology. We prove, among others,
that natural dense subspaces of $CLB_H(R^m)$ of all nowhere dense closed sets,
of all perfect sets, of all Cantor sets and of all Lebesgue measure zero sets
are homeomorphic to the Hilbert space $\ell_2$.
  Moreover, we investigate the hyperspace $CL_H(R)$ of all nonempty closed
subsets of the real line $R$ with the Hausdorff (infinite-valued) metric. We
show that a nonseparable component of $CL_H(R)$ is homeomorphic to the Hilbert
space $\ell_2(2^{\aleph_0})$ as long as it does not contain any of the sets $R,
[0,\infty), (-\infty,0]$.


title:
An Approximate Analytical Algorithm for Evaluating the Distances in a
  Dark Energy Dominated Universe

abstract:
  The most recent cosmological observations indicate that the present universe
is flat and vacuum dominated. In such a universe, the distance measurements are
always difficult and involve numerical computations. In this paper, it is shown
that the most fundamental distance measurement of cosmology, the luminosity
distance, for such a universe can be obtained in an approximate analytical way
with very small errors of less than 0.02% up to %z = 5$ for any value of vacuum
energy. The analytical calculation is shown to be exceedingly efficient, as
compared to the traditional numerical methods.


title:
D-modules on the affine flag variety and representations of affine
  Kac-Moody algebras

abstract:
  We study the connection between the category of modules over the affine
Kac-Moody Lie algebra at the critical level, and the category of D-modules on
the affine flag scheme G((t))/I, where I is the Iwahori subgroup.
  We prove a localization-type result, which establishes an equivalence between
certain subcategories on both sides.
  We also establish an equivalence between a certain subcategory of Kac-Moody
modules, and the category of quasi-coherent sheaves on the scheme of Miura
opers for the Langlands dual group, thereby proving a conjecture of [FG2].


title:
Quantum Computational Method of Finding the Ground State Energy and
  Expectation Values

abstract:
  We propose a new quantum computational way of obtaining a ground-state energy
and expectation values of observables of interacting Hamiltonians. It is based
on the combination of the adiabatic quantum evolution to project a ground state
of a non-interacting Hamiltonian onto a ground state of an interacting
Hamiltonian and the phase estimation algorithm to retrieve the ground-state
energy. The expectation value of an observable for the ground state is obtained
with the help of Hellmann-Feynman theorem. As an illustration of our method, we
consider a displaced harmonic oscillator, a quartic anharmonic oscillator,and a
potential scattering model. The results obtained by this method are in good
agreement with the known results.


title:
Glauber dynamics for the mean-field Ising model: cut-off, critical power
  law, and metastability

abstract:
  We study the Glauber dynamics for the Ising model on the complete graph, also
known as the Curie-Weiss Model. For beta < 1, we prove that the dynamics
exhibits a cut-off: the distance to stationarity drops from near 1 to near 0 in
a window of order n centered at [2(1-beta)]^{-1} n log n. For beta = 1, we
prove that the mixing time is of order n^{3/2}. For beta > 1, we study
metastability. In particular, we show that the Glauber dynamics restricted to
states of non-negative magnetization has mixing time O(n log n).


title: Microscopic Theory of Black Hole Superradiance

abstract:
  We study how black hole superradiance appears in string microscopic models of
rotating black holes. In order to disentangle superradiance from
finite-temperature effects, we consider an extremal, rotating D1-D5-P black
hole that has an ergosphere and is not supersymmetric. We explain how the
microscopic dual accounts for the superradiant ergosphere of this black hole.
The bound 0< omega < m Omega_H on superradiant mode frequencies is argued to be
a consequence of Fermi-Dirac statistics for the spin-carrying degrees of
freedom in the dual CFT. We also compute the superradiant emission rates from
both sides of the correspondence, and show their agreement.


title:
Tempered solutions of $\mathcal D$-modules on complex curves and formal
  invariants

abstract:
  Let $X$ be a complex analytic curve. In this paper we prove that the
subanalytic sheaf of tempered holomorphic solutions of $\mathcal D_X$-modules
induces a fully faithful functor on a subcategory of germs of formal holonomic
$\mathcal D_X$-modules. Further, given a germ $\mathcal M$ of holonomic
$\mathcal D_X$-module, we obtain some results linking the subanalytic sheaf of
tempered solutions of $\mathcal M$ and the classical formal and analytic
invariants of $\mathcal M$.


title:
Spiral inflow feeding the nuclear starburst in M83, observed in H-alpha
  emission with the GHAFAS Fabry-Perot interferometer

abstract:
  We present observations of the nearby barred starburst galaxy, M83 (NGC5236),
with the new Fabry-Perot interferometer GHAFAS mounted on the 4.2 meter William
Herschel Telescope on La Palma. The unprecedented high resolution observations,
of 16 pc/FWHM, of the H-alpha-emitting gas cover the central two kpc of the
galaxy. The velocity field displays the dominant disk rotation with signatures
of gas inflow from kpc scales down to the nuclear regions. At the inner Inner
Lindblad Resonance radius of the main bar and centerd at the dynamical center
of the main galaxy disk, a nuclear $5.5 (\pm 0.9) \times 10^8 M_\odot$ rapidly
rotating disk with scale length of $60 \pm 20$ pc has formed. The nuclear
starburst is found in the vicinity as well as inside this nuclear disk, and our
observations confirm that gas spirals in from the outer parts to feed the
nuclear starburst, giving rise to several star formation events at different
epochs, within the central 100 pc radius of M83.


title: A high-accuracy algorithm for designing arbitrary holographic atom traps

abstract:
  We report the realization of a new iterative Fourier-transform algorithm for
creating holograms that can diffract light into an arbitrary two-dimensional
intensity profile. We show that the predicted intensity distributions are
smooth with a fractional error from the target distribution at the percent
level. We demonstrate that this new algorithm outperforms the most frequently
used alternatives typically by one and two orders of magnitude in accuracy and
roughness, respectively. The techniques described in this paper outline a path
to creating arbitrary holographic atom traps in which the only remaining hurdle
is physical implementation.


title:
Asteroseismological measurements on PG 1159-035, the prototype of the GW
  Vir variable stars

abstract:
  An asteroseismological study of PG 1159-035, the prototype of the GW Vir
variable stars, has been performed on the basis of detailed and full PG1159
evolutionary models presented by Miller Bertolami & Althaus (2006). We carried
out extensive computations of adiabatic g-mode pulsation periods on PG1159
evolutionary models with stellar masses spanning the range 0.530 to 0.741 Mo.
We derive a stellar mass in the range 0.56-0.59 Mo from the period-spacing data
alone. We also find, on the basis of a period-fit procedure, a seismic model
representative of PG 1159-035 that reproduces the observed period pattern with
an average of the period differences of 0.64-1.03 s, consistent with the
expected model uncertainties. The results of the period-fit analysis carried
out in this work suggest that the surface gravity of PG 1159-035 would be 1
sigma larger than the spectroscopically inferred gravity. For our best-fit
model of PG 1159-035, all of the pulsation modes are characterized by positive
rates of period changes, at odds with the measurements by Costa & Kepler
(2007).


title:
$\theta_{13}$, $\delta$ and the neutrino mass hierarchy at a
  $\gamma=350$ double baseline Li/B $\beta$-Beam

abstract:
  We consider a $\beta$-Beam facility where $^8$Li and $^8$B ions are
accelerated at $\gamma = 350$, accumulated in a 10 Km storage ring and let
decay, so as to produce intense $\bar \nu_e$ and $\nu_e$ beams. These beams
illuminate two iron detectors located at $L \simeq 2000$ Km and $L \simeq 7000$
Km, respectively. The physics potential of this setup is analysed in full
detail as a function of the flux. We find that, for the highest flux ($10
\times 10^{18}$ ion decays per year per baseline), the sensitivity to
$\theta_{13}$ reaches $\sin^2 2 \theta_{13} \geq 2 \times10^{-4}$; the sign of
the atmospheric mass difference can be identified, regardless of the true
hierarchy, for $\sin^2 2 \theta_{13} \geq 4\times10^{-4}$; and, CP-violation
can be discovered in 70% of the $\delta$-parameter space for $\sin^2 2
\theta_{13} \geq 10^{-3}$, having some sensitivity to CP-violation down to
$\sin^2 2 \theta_{13} \geq 10^{-4}$ for $|\delta| \sim 90^\circ$.


title:
Calculating the Charged Particle Stopping Power Exactly to Leading and
  Next-to-leading Order

abstract:
  I will discuss a new method for calculating transport quantities, such as the
charged particle stopping power, in a weakly to moderately coupled plasma. This
method, called dimensional continuation, lies within the framework of
convergent kinetic equations, and it is powerful enough to allow for systematic
perturbative expansions in the plasma coupling constant. In particular, it
provides an exact evaluation of the stopping power to leading and
next-to-leading order in the plasma coupling, with the systematic error being
of cubic order. Consequently, the calculation is near-exact for a weakly
coupled plasma, and quite accurate for a moderately coupled plasma. The leading
order term in this expansion has been known since the classic work of Spitzer.
In contrast, the next-to-leading order term has been calculated only recently
by Brown, Preston, and Singleton (BPS), using the aforementioned method, to
account for all short- and long-distance physics accurate to second order in
the plasma coupling, including an exact treatment of the quantum-to-classical
scattering transition. Preliminary numerical studies suggest that the BPS
stopping power increases the ignition threshold, thereby having potential
adverse implications for upcoming high energy density facilities. Since the key
ideas behind the BPS calculation are possibly unfamiliar to plasma physicists,
and the implications might be important, I will use this opportunity to explain
the method in a pedagogical fashion.


title:
Rough solutions of the Einstein constraints on closed manifolds without
  near-CMC conditions

abstract:
  We consider the conformal decomposition of Einstein's constraint equations
introduced by Lichnerowicz and York, on a closed manifold. We establish
existence of non-CMC weak solutions using a combination of a priori estimates
for the individual Hamiltonian and momentum constraints, barrier constructions
for the Hamiltonian constraint, and topological fixed-point arguments. An
important new feature of these results is the absense of the near-CMC
assumption when the rescaled background metric is in the positive Yamabe class,
if the freely specifiable part of the data given by the matter fields (if
present) and the traceless-transverse part of the rescaled extrinsic curvature
are taken to be sufficiently small. In this case, the mean extrinsic curvature
can be taken to be an arbitrary smooth function without restrictions on the
size of its spatial derivatives, giving what are apparently the first non-CMC
existence results without the near-CMC assumption. Standard bootstrapping
arguments to increase the regularity of the conformal factor are blocked by the
use of a weak background metric. In the CMC case, we recover Maxwell's rough
solution results as a special case. Our results extend the 1996 non-CMC result
of Isenberg and Moncrief in three ways: (1) the near-CMC assumption is removed
in the case of the positive Yamabe class; (2) regularity is extended down to
the maximum allowed by the background metric and the matter; and (3) the result
holds for all three Yamabe classes. This last extension was also accomplished
recently by Allen, Clausen and Isenberg, although their result is restricted to
the near-CMC case and to smoother background metrics and data.


title: Modelling the formation and evolution of disk galaxies

abstract:
  Inspired by recent work on feedback in disk galaxies (Efstathiou 2000, Silk
2003) and on the angular momentum distribution in simulated gas halos (Sharma
and Steinmetz 2005), a fully dynamic model of disk galaxy formation and
evolution has been developed. This is used to demonstrate how observed galactic
systems could have formed from halos similar to those found in simulations and
applies physically motivated models of star formation and feedback to explore
whether the true nature of these processes would be manifest from local and
cosmological observables. This is made possible by computational integration
with the galaxy formation model developed originally by the group at Durham
University (Cole et al. 2000).


title: How non-magnetic are "non-magnetic" Herbig Ae/Be stars?

abstract:
  Our recent discovery of magnetic fields in a small number of Herbig Ae/Be
stars has required that we survey a much larger sample of stars. From our FORS1
and ESPaDOnS surveys, we have acquired about 125 observations of some 70 stars
in which no magnetic fields are detected. Using a Monte Carlo approach, we have
performed statistical comparisons of the observed longitudinal fields and LSD
Stokes V profiles of these apparently non-magnetic stars with a variety of
field models. This has allowed us to derive general upper limits on the
presence of dipolar fields in the sample, and to place realistic upper limits
on undetected dipole fields which may be present in individual stars. This
paper briefly reports the results of the statistical modeling, as well as field
upper limits for individual stars of particular interest.


title:
Elastic systems with correlated disorder: Response to tilt and
  application to surface growth

abstract:
  We study elastic systems such as interfaces or lattices pinned by correlated
quenched disorder considering two different types of correlations: generalized
columnar disorder and quenched defects correlated as ~ x^{-a} for large
separation x. Using functional renormalization group methods, we obtain the
critical exponents to two-loop order and calculate the response to a transverse
field h. The correlated disorder violates the statistical tilt symmetry
resulting in nonlinear response to a tilt. Elastic systems with columnar
disorder exhibit a transverse Meissner effect: disorder generates the critical
field h_c below which there is no response to a tilt and above which the tilt
angle behaves as \theta ~ (h-h_c)^{\phi} with a universal exponent \phi<1. This
describes the destruction of a weak Bose glass in type-II superconductors with
columnar disorder caused by tilt of the magnetic field. For isotropic
long-range correlated disorder, the linear tilt modulus vanishes at small
fields leading to a power-law response \theta ~ h^{\phi} with \phi>1. The
obtained results are applied to the Kardar-Parisi-Zhang equation with
temporally correlated noise.


title: High Energy Scattering in the AdS/CFT Correspondence

abstract:
  This work explores the celebrated AdS/CFT correspondence in the regime of
high energy scattering in Anti--de Sitter (AdS) spacetime. In particular, we
develop the eikonal approximation to high energy scattering in AdS and explore
its consequences for the dual Conformal Field Theory (CFT).
  Using position space Feynman rules, we rederive the eikonal approximation for
high energy scattering in flat space. Following this intuitive position space
perspective, we then generalize the eikonal approximation for high energy
scattering in AdS and other spacetimes. Remarkably, we are able to resum, in
terms of a generalized phase shift, ladder and cross ladder Witten diagrams
associated to the exchange of an AdS spin j field, to all orders in the
coupling constant.
  By the AdS/CFT correspondence, the eikonal amplitude in AdS is related to the
four point function of CFT primary operators in the regime of large 't Hooft
coupling, including all terms of the 1/N expansion. We then show that the
eikonal amplitude determines the behavior of the CFT four point function for
small values of the cross ratios in a Lorentzian regime and that this controls
its high spin and dimension conformal partial wave decomposition. These results
allow us to determine the anomalous dimension of high spin and dimension double
trace primary operators, by relating it to the AdS eikonal phase shift. Finally
we find that, at large energies and large impact parameters in AdS, the
gravitational interaction dominates all other interactions, as in flat space.
Therefore, the anomalous dimension of double trace operators, associated to
graviton exchange in AdS, yields a universal prediction for CFT's with AdS
gravitational duals.


title:
Measurement of the shape of the boson transverse momentum distribution
  in ppbar -> Z/gamma* -> ee+X events produced at sqrt{s}=1.96 TeV

abstract:
  We present a measurement of the shape of the Z/gamma* boson transverse
momentum (qT) distribution in ppbar -> Z/gamma* -> ee+X events at a
center-of-mass energy of 1.96 TeV using 0.98 fb-1 of data collected with the D0
detector at the Fermilab Tevatron collider. The data are found to be consistent
with the resummation prediction at low qT, but above the perturbative QCD
calculation in the region of qT>30 GeV/c. Using events with qT<30 GeV/c, we
extract the value of g2, one of the non-perturbative parameters for the
resummation calculation. Data at large boson rapidity y are compared with the
prediction of resummation and with alternative models that employ a resummed
form factor with modifications in the small Bjorken x region of the proton wave
function.


title:
Minimum Cost Homomorphisms to Locally Semicomplete and Quasi-Transitive
  Digraphs

abstract:
  For digraphs $G$ and $H$, a homomorphism of $G$ to $H$ is a mapping $f:\
V(G)\dom V(H)$ such that $uv\in A(G)$ implies $f(u)f(v)\in A(H)$. If, moreover,
each vertex $u \in V(G)$ is associated with costs $c_i(u), i \in V(H)$, then
the cost of a homomorphism $f$ is $\sum_{u\in V(G)}c_{f(u)}(u)$. For each fixed
digraph $H$, the minimum cost homomorphism problem for $H$, denoted
MinHOM($H$), can be formulated as follows: Given an input digraph $G$, together
with costs $c_i(u)$, $u\in V(G)$, $i\in V(H)$, decide whether there exists a
homomorphism of $G$ to $H$ and, if one exists, to find one of minimum cost.
Minimum cost homomorphism problems encompass (or are related to) many well
studied optimization problems such as the minimum cost chromatic partition and
repair analysis problems. We focus on the minimum cost homomorphism problem for
locally semicomplete digraphs and quasi-transitive digraphs which are two
well-known generalizations of tournaments. Using graph-theoretic
characterization results for the two digraph classes, we obtain a full
dichotomy classification of the complexity of minimum cost homomorphism
problems for both classes.


title: Viscosity Bound Violation in Higher Derivative Gravity

abstract:
  Motivated by the vast string landscape, we consider the shear viscosity to
entropy density ratio in conformal field theories dual to Einstein gravity with
curvature square corrections. After field redefinitions these theories reduce
to Gauss-Bonnet gravity, which has special properties that allow us to compute
the shear viscosity nonperturbatively in the Gauss-Bonnet coupling. By tuning
of the coupling, the value of the shear viscosity to entropy density ratio can
be adjusted to any positive value from infinity down to zero, thus violating
the conjectured viscosity bound. At linear order in the coupling, we also check
consistency of four different methods to calculate the shear viscosity, and we
find that all of them agree. We search for possible pathologies associated with
this class of theories violating the viscosity bound.


title: Modeling disorder in graphene

abstract:
  We present a study of different models of local disorder in graphene. Our
focus is on the main effects that vacancies -- random, compensated and
uncompensated --, local impurities and substitutional impurities bring into the
electronic structure of graphene. By exploring these types of disorder and
their connections, we show that they introduce dramatic changes in the low
energy spectrum of graphene, viz. localized zero modes, strong resonances, gap
and pseudogap behavior, and non-dispersive midgap zero modes.


title: Conformal deformation of spacelike surfaces in Minkowski space

abstract:
  We address the problem of second order conformal deformation of spacelike
surfaces in compactified Minkowski 4-space. We explain the construction of the
exterior differential system of conformal deformations and discuss its general
and singular solutions. In particular, we show that isothermic surfaces are
singular solutions of the system, which implies that a generic second order
deformable surface is not isothermic. This differs from the situation in
3-dimensional conformal geometry, where isothermic surfaces coincide with
deformable surfaces.


title: On the Collision of Cosmic Superstrings

abstract:
  We study the formation of three-string junctions between (p,q)-cosmic
superstrings, and collisions between such strings and show that kinematic
constraints analogous to those found previously for collisions of Nambu-Goto
strings apply here too, with suitable modifications to take account of the
additional requirements of flux conservation. We examine in detail several
examples involving collisions between strings with low values of p and q, and
also examine the rates of growth or shrinkage of strings at a junction.
Finally, we briefly discuss the formation of junctions for strings in a warped
space, specifically with a Klebanov-Strassler throat, and show that similar
constraints still apply with changes to the parameters taking account of the
warping and the background flux.


title:
Vertical stratification of iron abundance in atmospheres of blue
  horizontal-branch stars

abstract:
  The observed slow rotation and abundance peculiarities of certain blue
horizontal branch (BHB) stars suggests that atomic diffusion can be important
in their stellar atmospheres and can lead to vertical abundance stratification
of chemical species in the atmosphere. To verify this hypothesis, we have
undertaken an abundance stratification analysis in the atmospheres of six BHB
stars, based on recently acquired McDonald-CE spectra. Our numerical
simulations show that the iron abundance is vertically stratified in the
atmospheres of two stars in M15: B267 and B279. One star WF2-2541 in M13 also
appears to have vertically stratified iron abundance, while for WF4-3085 the
signatures of iron stratification are less convincing. In all cases the iron
abundances increase towards the lower atmosphere. The other two stars in our
sample, WF4-3485 and B84, do not show any significant variation of iron with
atmospheric depth. Our results support the idea that atomic diffusion dominates
other hydrodynamic processes in the atmospheres of BHB stars.


title: Emergent rainbow spacetimes: Two pedagogical examples

abstract:
  There is a possibility that spacetime itself is ultimately an emergent
phenomenon, a near-universal "low-energy long-distance approximation", similar
to the way in which fluid mechanics is the near-universal low-energy
long-distance approximation to quantum molecular dynamics. If so, then direct
attempts to quantize spacetime are misguided - at least as far as fundamental
physics is concerned. Based on this and other considerations, there has
recently been a surge of interest in the notion of energy-dependent and
momentum-dependent "rainbow'' geometries. In the present article I will not
discuss these exotic ideas in any detail, instead I will present two specific
and concrete examples of situations where an energy-dependent "rainbow''
geometry makes perfectly good mathematical and physical sense. These simple
examples will then serve as templates suggesting ways of proceeding in
situations where the underlying physics may be more complex. The specific
models I will deal with are (1) acoustic spacetimes in the presence of
nontrivial dispersion, and (2) a mathematical reinterpretation of Newton's
second law for a non-relativistic conservative force, which is well-known to be
equivalent to the differential geometry of an energy-dependent conformally flat
three-manifold. These two models make it clear that there is nothing wrong with
the concept of an energy-dependent "rainbow'' geometry per se. Whatever
problems may arise in the implementation of any specific
quantum-gravity-inspired proposal for an energy-dependent spacetime are related
to deeper questions regarding the compatibility of that specific proposal with
experimental reality.


title: The Fast Fibonacci Decompression Algorithm

abstract:
  Data compression has been widely applied in many data processing areas.
Compression methods use variable-size codes with the shorter codes assigned to
symbols or groups of symbols that appear in the data frequently. Fibonacci
coding, as a representative of these codes, is used for compressing small
numbers. Time consumption of a decompression algorithm is not usually as
important as the time of a compression algorithm. However, efficiency of the
decompression may be a critical issue in some cases. For example, a real-time
compression of tree data structures follows this issue. Tree's pages are
decompressed during every reading from a secondary storage into the main
memory. In this case, the efficiency of a decompression algorithm is extremely
important. We have developed a Fast Fibonacci decompression for this purpose.
Our approach is up to $3.5\times$ faster than the original implementation.


title: A Survey of 3.3 Micron PAH Emission in Planetary Nebulae

abstract:
  Results are presented from a pilot survey of 3.3 micron PAH emission from
planetary nebulae using FLITECAM, an instrument intended for airborne astronomy
with SOFIA. The observations were made during ground-based commissioning of
FLITECAM's spectroscopic mode at the 3-m Shane telescope at Lick Observatory.
Direct-ruled KRS-5 grisms were used to give a resolving power (R)~1,700.
Targets were selected from IRAS, KAO and ISO sources with previously observed
PAH emission at longer wavelengths. AGB stars and PN with C/O ratios < 1 were
also added to the target list in order to test PAH detection thresholds. In
all, 20 objects were observed. PAH emission was detected in 11 out of 20
observed targets.