abstract
stringlengths 6
6.09k
| id
stringlengths 9
16
| time
int64 725k
738k
|
|---|---|---|
In this paper we consider the bilocal field approach for $QCD$. We obtain a
bilocal effective meson action with a potential kernel given in relativistic
covariant form. The corresponding Schwinger--Dyson and Bethe--Salpeter
equations are investigated in detail. By introducing weak interactions into the
theory we study heavy meson properties as decay constants and semileptonic
decay amplitudes. Thereby, the transition from the bilocal field description to
the heavy quark effective theory is discussed. Considering as example the
semileptonic decay of a pseudoscalar $B$--meson into a pseudoscalar $D$--meson
we obtain an integral expression for the corresponding Isgur--Wise function in
terms of meson wave functions.
|
hep-ph/9208261
| 727,441 |
A Fock representation of the quantum affine algebra $U_q(\widehat{\sl}_2)$ is
constructed by three bosonic fields for an arbitrary level with the help of the
Drinfeld realization.
|
hep-th/9208079
| 727,441 |
We show how a 17 keV neutrino, the solar neutrino problem, and the
atmospheric muon-neutrino deficit could all be the low-energy residues of the
same pattern of lepton-number breaking at and above the weak scale, with no
requirement for fine-tuning a symmetry-breaking scale at lower energies. Talk
given at ``Beyond the Standard Model III'', Carleton University, June 1992.
|
hep-ph/9208262
| 727,441 |
By applying the Dirac quantization method, we build the constraint that all
electrons are in the lowest Landau level into the Chern-Simons field theory
approach for the fractional quantum Hall system and show that the constraint
can be transmuted from hierarchy to hierarchy. For a finite system, we derive
that the action for each hierarchy can be split into two parts: a surface part
provides the action for the edge excitations while the remaining part is
precisely the bulk action for the next hierarchy. And the action for the edge
could be decoupled from the bulk only at the hierarchy filling.
|
cond-mat/9209001
| 727,441 |
The electromagnetic response of a pinned Abrikosov fluxoid is examined in the
framework of the Bogoliubov-de Gennes formalism. The matrix elements and the
selection rules for both the single photon (emission - absorption) and two
photon (Raman scattering) processes are obtained. The results reveal striking
asymmetries: light absorption by quasiparticle pair creation or single
quasiparticle scattering can occur only if the handedness of the incident
radiation is opposite to that of the vortex core states. We show how these
effects will lead to nonreciprocal circular birefringence, and also predict
structure in the frequency dependence of conductivity and in the differential
cross section of the Raman scattering.
|
cond-mat/9208026
| 727,441 |
Spin-orbit interaction produces persistent spin and mass currents in the ring
via the Aharonov-Casher effect. The experiment in $^3He-A_1$ phase, in which
this effect leads to the excitation of mass and spin supercurrent is proposed.
|
cond-mat/9208027
| 727,441 |
Let $G\subset GL(V)$ be a linear Lie group with Lie algebra $\frak g$ and let
$A(\frak g)^G$ be the subalgebra of $G$-invariant elements of the associative
supercommutative algebra $A(\frak g)= S(\frak g^*)\otimes \La(V^*)$. To any
$G$-structure $\pi:P\to M$ with a connection $\omega$ we associate a
homomorphism $\mu_\omega:A(\frak g)^G\to \Omega(M)$. The differential forms
$\mu_\omega(f)$ for $f\in A(\frak g)^G$ which are associated to the
$G$-structure $\pi$ can be used to construct Lagrangians. If $\omega$ has no
torsion the differential forms $\mu_\omega(f)$ are closed and define
characteristic classes of a $G$-structure. The induced homomorphism
$\mu'_\omega:A(\g)^G\to H^*(M)$ does not depend on the choice of the
torsionfree connection $\omega$ and it is the natural generalization of the
Chern Weil homomorphism.
|
math/9209219
| 727,442 |
This paper investigates the existence of Denjoy minimal sets and, more
generally, strictly ergodic sets in the dynamics of iterated homeomorphisms. It
is shown that for the full two-shift, the collection of such invariant sets
with the weak topology contains topological balls of all finite dimensions. One
implication is an analogous result that holds for diffeomorphisms with
transverse homoclinic points. It is also shown that the union of Denjoy minimal
sets is dense in the two-shift and that the set of unique probability measures
supported on these sets is weakly dense in the set of all shift-invariant,
Borel probability measures.
|
math/9209220
| 727,442 |
The Liouville approach is applied to the quantum treatment of the dilaton
gravity in two dimensions. The physical states are obtained from the BRST
cohomology and correlation functions are computed up to three-point functions.
For the $N=0$ case (i.e., without matter), the cosmological term operator is
found to have the discrete momentum that plays a special role in the $c=1$
Liouville gravity. The correlation functions for arbitrary numbers of operators
are found in the $N=0$ case, and are nonvanishing only for specific
``chirality'' configurations.
|
hep-th/9208080
| 727,442 |
We generalize the Goddard-Kent-Olive (GKO) coset construction to the
dimension 5/2 operator for $ \hat{so} (5) $ and compute the fourth order
Casimir invariant in the coset model $\hat{SO} (5)_{1} \times \hat{SO}
(5)_{m} / \hat{SO} (5)_{1+m} $ with the generic unitary minimal $ c < 5/2 $
series that can be viewed as perturbations of the $ m \rightarrow \infty $
limit, which has been investigated previously in the realization of $ c= 5/2 $
free fermion model.
|
hep-th/9209001
| 727,442 |
We present a notion of symmetry for 1+1-dimensional integrable systems which
is consistent with their group theoretic description and reproduces in special
cases the known Baecklund transformation for the generalized Korteweg-deVries
hierarchies. We also apply it to the relativistic invariance of the
Leznov-Saveliev systems.
|
hep-th/9209004
| 727,442 |
We present the results of the influence of the minimal supersymmetric
standard model extended by an additional
Higgs singlet N, with vacuum expectation value $v_N$, on the anomalous
magnetic moment of the muon.
This gives different mass matrices for the charginos and neutralinos, which
are taken into account within the relevant penguin diagrams leading to a
contribution $\Delta a_{\mu}$\ to the anomalous magnetic moment of the muon. We
show that a large vacuum expectation value for the Higgs singlet leads to a
suppression of the supersymmetric contribution making it difficult to see in an
experiment in the near future.}\hfill
|
hep-ph/9209201
| 727,442 |
Pure SU(2) gauge theory is the simplest asymptotically free theory in four
dimensions. To investigate Euclidean quantum gravity effects in a fundamental
length scenario, we simulate 4$d$ SU(2) lattice gauge theory on a dynamically
coupled Regge skeleton. The fluctuations of the skeleton are governed by the
standard Regge-Einstein action. From a small $2\cdot 4^3$ lattice we report
exploratory numerical results, limited to a region of strong gravity where the
Planck mass and hadronic masses take similar orders of magnitude. We find a
range of the Planck mass where stable bulk expectation values are obtained
which vary smoothly with the gauge coupling, and a remnant of the QCD
deconfining phase transition is located. Note: The full ps file of this
preprint is also available via anonymous ftp to ftp.scri.fsu.edu. To get the ps
file, ftp to this address and use for username "anonymous" and for password
your name. The file is in the directory pub/krishnan (to go to that directory
type: cd pub/krishnan) and is called gravity.ps (to get it type: get
gravity.ps). If you have any problems send mail to [email protected].
|
hep-lat/9209001
| 727,442 |
We determine the critical momenta for chiral fermions in the domain wall
model recently suggested by Kaplan. For a wide range of domain wall masses $m$
and Wilson couplings $r$ we explicitly exhibit the regions in momentum space
where the fermions are chiral. We compare the critical momenta for the
infinitely large system with those obtained on a finite lattice.
|
hep-lat/9209002
| 727,442 |
The potential energy of a static charge distribution on a lattice is
rigorously computed in the standard compact quantum electrodynamic model. The
method used follows closely that of Weyl for ordinary quantum electrodynamics
in continuous space-time. The potential energy of the static charge
distribution is independent of temperature and can be calculated from the
lattice version of Poisson's equation. It is the usual Coulomb potential.
|
hep-ph/9209202
| 727,442 |
The solution of the classical field equation generates the sum of all tree
graphs. We show that the classical equation reduces to an easily solved
ordinary differential equation for certain multiparticle threshold amplitudes
and compute these amplitudes.
|
hep-ph/9209203
| 727,442 |
The Adler-Kostant-Symes $R$-bracket scheme is applied to the algebra of
pseudo-differential operators to relate the three integrable hierarchies: KP
and its two modifications, known as nonstandard integrable models. All three
hierarchies are shown to be equivalent and connection is established in the
form of a symplectic gauge transformation. This construction results in a new
representation of the W-infinity algebras in terms of 4 bosonic fields.
|
hep-th/9209006
| 727,442 |
We compute the polarisability of the nucleon to leading order in chiral
perturbation theory. The contributions from kaons and baryon resonances as
intermediate states are included in addition to the contribution from pions and
nucleons that had been previously computed. The isoscalar operators are
dominated by the infrared behaviour of pion loops giving rise to a $1/m_{\pi}$
coefficient. In contrast, the isovector operators are dominated by loops
involving kaons, giving a $1/m_{k}$ coefficient, and further demonstrates that
the strange quark is an important component of the nucleon. In addition, the
inclusion of the decuplet of baryon resonances as intermediate states
substantially modifies the result found from the octet baryons alone for the
isoscalar polarisability.
|
hep-ph/9209204
| 727,442 |
We compute the Chern-Simons current induced by Wilson fermions on a $d=2n+1$
dimensional lattice, making use of a topological interpretation of the momentum
space fermion propagator as a map from the torus to the sphere, $T^{d}\to
S^{d}$. These mappings are shown to fall in different homotopy classes
depending on the value of $m/r$, where $m$ is the fermion mass and $r$ is the
Wilson coupling. As a result, the induced Chern-Simons term changes
discontinuously at $d+1$ different values for $m$, unlike in the continuum.
This behavior is exactly what is required by the peculiar spectrum found for a
recently proposed model of chiral lattice fermions as zeromodes bound to a
domain wall.
|
hep-lat/9209003
| 727,442 |
The finite temperature phase diagram of a U(1) Higgs-Yukawa model at a finite
value of the scalar self coupling $\lambda$ is investigated by means of a
large-$N_f$ calculation and numerical simulations. The phase diagram is similar
to the one at zero temperature and shows a ferromagnetic, two symmetric and an
antiferromagnetic phase. However, the phase transition lines are shifted to
larger values of the Yukawa coupling demonstrating the occurence of the finite
temperature symmetry restoration.
|
hep-lat/9209004
| 727,442 |
An overview is given over the recently developed and now widely used Monte
Carlo algorithms with reduced or eliminated critical slowing down. The basic
techniques are overrelaxation, cluster algorithms and multigrid methods. With
these tools one is able to probe much closer than before the universal
continuum behavior of field theories on the lattice.
|
hep-lat/9209005
| 727,443 |
We study the discrete state structure of $\hat c=1$ superconformal matter
coupled to 2-D supergravity. Factorization properties of scattering amplitudes
are used to identify these states and to construct the corresponding vertex
operators. For both Neveu-Schwarz and Ramond sectors these states are shown to
be organized in
SU(2) multiplets. The algebra generated by the discrete states is computed in
the limit of null cosmological constant.
|
hep-th/9209010
| 727,443 |
We examine the production of a new $Z'$ gauge boson in association with
photons or jets at future hadron supercolliders as a probe of its couplings to
fermions. Associated jet production is found to be rather insensitive to these
couplings and suffers from large uncertainties as well as substantial
backgrounds. On the other hand, the ratio of rates for associated photon $Z'$
production to that of conventional $Z'$ production has a rather clean signature
(once appropriate cuts are made), and is found to be quite sensitive to the
choice of extended electroweak model, while being simultaneously insensitive to
structure function uncertainties and QCD corrections. Rates at both the SSC and
LHC are significant for $Z'$ masses in the 1 TeV range.
|
hep-ph/9209207
| 727,443 |
Black hole evaporation may lead to massive or massless remnants, or naked
singularities. This paper investigates this process in the context of two quite
different two dimensional black hole models. The first is the original CGHS
model, the second is another two dimensional dilaton-gravity model, but with
properties much closer to physics in the real, four dimensional, world.
Numerical simulations are performed of the formation and subsequent evaporation
of black holes and the results are found to agree qualitatively with the
exactly solved modified CGHS models, namely that the semiclassical
approximation breaks down just before a naked singularity appears.
|
hep-th/9209008
| 727,443 |
We present the extension of the Wakimoto construction to the $su(2)_k$
quantum current algebra and its associated $Z_k$ quantum parafermion algebra.
This construction is achieved in terms of various deformations of three
classical free boson fields. We also give the vertex operators corresponding to
the quantum spin-$j$ representation.
|
hep-th/9209009
| 727,443 |
Regge theory provides a very simple and economical description of all total
cross sections
|
hep-ph/9209205
| 727,443 |
Zee-type models with Majorons naturally incorporate the 17 keV neutrino but
in their minimal version fail to simultaneously solve the solar neutrino
puzzle. If there is a sterile neutrino state, we find a particularly simple
solution to the solar neutrino problem, which besides $\nu_{17}$ predicts a
light Zeldovich-Konopinski-Mahmoud neutrino $\nu_{light}=\nu_e+\nu_{\mu}^c$
with a magnetic moment being easily as large as $10^{-11}\mu_B$ through the
Barr-Freire-Zee mechanism.
|
hep-ph/9209206
| 727,443 |
The local Lorentz and diffeomorphism symmetries of Einstein's gravitational
theory are spontaneously broken by a Higgs mechanism by invoking a phase
transition in the early Universe, at a critical temperature $T_c$ below which
the symmetry is restored. The spontaneous breakdown of the vacuum state
generates an external time and the wave function of the Universe satisfies a
time dependent Schrodinger equation, which reduces to the Wheeler-deWitt
equation in the classical regime for $T < T_c$, allowing a semi-classical WKB
approximation to the wave function. The conservation of energy is spontaneously
violated for $T > T_c$ and matter is created fractions of seconds after the big
bang, generating the matter in the Universe. The time direction of the vacuum
expectation value of the scalar Higgs field generates a time asymmetry, which
defines the cosmological arrow of time and the direction of increasing entropy
as the Lorentz symmetry is restored at low temperatures.
|
gr-qc/9209001
| 727,443 |
Our theme is that not every interesting question in set theory is independent
of $ZFC$. We give an example of a first order theory $T$ with countable $D(T)$
which cannot have a universal model at $\aleph_1$ without CH; we prove in $ZFC$
a covering theorem from the hypothesis of the existence of a universal model
for some theory; and we prove --- again in ZFC --- that for a large class of
cardinals there is no universal linear order (e.g. in every
$\aleph_1<\l<2^{\aleph_0}$). In fact, what we show is that if there is a
universal linear order at a regular $\l$ and its existence is not a result of a
trivial cardinal arithmetical reason, then $\l$ ``resembles'' $\aleph_1$ --- a
cardinal for which the consistency of having a universal order is known. As for
singular cardinals, we show that for many singular cardinals, if they are not
strong limits then they have no universal linear order. As a result of the non
existence of a universal linear order, we show the non-existence of universal
models for all theories possessing the strict order property (for example,
ordered fields and groups, Boolean algebras, p-adic rings and fields, partial
orders, models of PA and so on).
|
math/9209201
| 727,444 |
In Binder's approach the reduced interface tension sigma of the Ising model
in the broken phase is determined from the finite volume effects of the
partition function Z(M) at fixed total magnetization M. For small |M| the
partition function of a system of size L^d with periodic boundary conditions is
dominated by configurations with two interfaces, such that Z(M) ~ exp(- 2 sigma
L^{d-1}). Capillary wave fluctuations of the interfaces correct this result to
Z(M) ~ exp(- 2 sigma L^{d-1}) with x = -1. The knowledge of the pre-exponential
behavior allows an improved fit of numerical data, and a determination of the
interface stiffness.
|
hep-lat/9209006
| 727,444 |
We examine discrete gauge symmetries in axionic extensions of the SSM which
provide a solution of the $\mu$-problem. Automatic-PQ symmetry and proton
stability are shown to be guaranteed by certain discrete symmetries. Focusing
on the L-violating discrete symmetries we discuss two sources of neutrino
masses and their relevance for the solar neutrino problem.
|
hep-ph/9209208
| 727,444 |
We systematically analyze the decay of metastable topological defects that
arise from the spontaneous breakdown of gauge or global symmetries.
Quantum-mechanical tunneling rates are estimated for a variety of decay
processes. The decay rate for a global string, vortex, domain wall, or kink is
typically suppressed compared to the decay rate for its gauged counterpart. We
also discuss the decay of global texture, and of semilocal and electroweak
strings.
|
hep-ph/9209210
| 727,444 |
We measure accurate values of the inter-quark potentials on a $48^{3}56$
lattice with SU(2) pure gauge theory at $ \beta =2.85$. The scale is set by
extracting the string tension - we obtain ${\sqrt K}a=0.063(3)$ at $\beta
=2.85.$ From a careful study of the small-$R$ potentials in the region 2 GeV $<
R^{-1} < 5$ GeV, we extract a running coupling constant and estimate the scale
$\Lambda _{\msbar} = 272(24)$ MeV.
|
hep-lat/9209007
| 727,444 |
{}From an accurate determination of the inter-quark potential, one can study
the running coupling constant for a range of $R$-values and hence estimate the
scale $\Lambda_{\msbar} $. Detailed results are presented for $SU(3)$ pure
gauge theory.
|
hep-lat/9209008
| 727,444 |
Analyses which use loop calculations to put constraints on anomalous
trilinear gauge boson couplings (TGC's) often give bounds which are much too
stringent. The reason has nothing to do with gauge invariance, in contrast to
the recent claims of de Rujula et. al., since the lagrangians used in these
calculations ARE gauge invariant, with the SU(2)L X U(1)Y symmetry nonlinearly
realized. We trace the true cause of the problem to the improper interpretation
of cutoffs in the calculation. The point is that the cutoff dependence of a
loop integral does not necessarily reflect the true dependence on the heavy
physics scale M. We illustrate that, if done carefully, one finds that the true
constraints on anomalous TGC's are much weaker.
|
hep-ph/9209211
| 727,444 |
We present a new model describing strongly correlated electrons on a general
$d$-dimensional lattice. It differs from the Hubbard model by interactions of
nearest neighbours, and it contains the $t$-$J$ model as a special case. The
model naturally describes local electron pairs, which can move coherently at
arbitrary momentum. By using an $\eta$-pairing mechanism we can construct
eigenstates of the hamiltonian with off-diagonal-long-range-order (ODLRO).
These might help to relate the model to high-$T_c$ superconductivity. On a
one-dimensional lattice, the model is exactly solvable by Bethe Ansatz.
|
cond-mat/9209002
| 727,444 |
We present a theoretical and numerical investigation of the effect of a
time-varying external driving force on interface growth. First, we derive a
relation between the roughening exponents which comes from a generalized
Galilean invariance, showing how the critical dimension of the model is tunable
with the external field. We further conjecture results for the exponents in two
dimensions, and find consistency with data obtained through simulations of two
models we expect to be in the same universality class. Finally, we discuss how
our results can be investigated experimentally.
|
cond-mat/9209003
| 727,445 |
The rule relating the observed Hall coefficient to the spin and charge
responses of the uniform doped Mott insulator is derived. It is essential to
include the contribution of holon and spinon three-current correlations to the
effective action of the gauge field. In the vicinity of the Mott insulating
point the Hall coefficient is holon dominated and weakly temperature dependent.
In the vicinity of a point of charge conjugation symmetry the holon
contribution to the observed Hall coefficient is small: the Hall coefficient
follows the temperature dependence of the diamagnetic susceptibility with a
sign determined by the Fermi surface shape. NOTE: document prepared using
REVTEX. (3 Figs, not included, available on request from: [email protected])
|
cond-mat/9209004
| 727,445 |
Our answer is the latter. Space-time singularities, including the initial
one, are described by world-sheet topological Abelian gauge theories with a
Chern-Simons term. Their effective $N=2$ supersymmetry provides an initial
fixed point where the Bogomolny bound is saturated on the world-sheet,
corresponding to an extreme Reissner-Nordstrom solution in space-time. Away
from the singularity the gauge theory has world-sheet matter fields, bosons and
fermions, associated with the generation of target space-time. Because the
fermions are complex (cf the Quantum Hall Effect) rather than real (cf
high-$T_c$ superconductors) the energetically-preferred vacuum is not parity or
time-reversal invariant, and the associated renormalization group flow explains
the cosmological arrow of time, as well as the decay of real or virtual black
holes, with a monotonic increase in entropy.
|
hep-th/9209013
| 727,445 |
Lectures Given at the Nato Advanced Study Institute-Particle Production in
Highly Excited Matter Il Ciocco, Italy July 1992 figure available on request.
Input harvmac.tex
|
hep-ph/9209212
| 727,445 |
We simulate four flavor noncompact lattice QED using the Hybrid Monte Carlo
algorithm on $10^4$ and $16^4$ lattices. Measurements of the monopole
susceptibility and the percolation order parameter indicate a transition at
$\beta = {1/e^2} = .205(5)$ with critical behavior in the universality class of
four dimensional percolation. We present accurate chiral condensate
measurements and monitor finite size effects carefully. The chiral condensate
data supports the existence of a power-law transition at $\beta = .205$ in the
same universality class as the chiral transition in the two flavor model. The
resulting equation of state predicts the mass ratio $m_\pi^2/m_\sigma^2$ in
good agreement with spectrum calculations while the hypothesis of a
logarithmically improved mean field theory fails qualitatively.
|
hep-lat/9209009
| 727,445 |
We discuss chiral symmetry breaking critical points from the perspective of
PCAC, correlation length scaling and the chiral equation of state. A scaling
theory for the ratio $R_\pi$ of the pion to sigma masses is presented. The
Goldstone character of the pion and properties of the longitudinal and
transverse chiral susceptibilities determine the ratio $R_\pi$ which can be
used to locate critical points and measure critical indices such as $\delta$.
We show how PCAC and correlation length scaling determine the pion mass'
dependence on the chiral condensate and lead to a practical method to measure
the anomalous dimension $\eta$. These tools are proving useful in studies of
the chiral transition in lattice QED and the quark-gluon plasma transition in
lattice QCD.
|
hep-lat/9209010
| 727,445 |
We present an ansatz for the quark and lepton mass matrices, derivable from
SO(10) type GUTs, which accommodates a heavy $(> 92 GeV)$ top quark and permits
large mixings in the $\nu_\mu \leftrightarrow \nu_\tau$ sector (as suggested by
the recent Kamiokande and IMB data on the atmospheric neutrinos). The well
known asymptotic relations $m_b = m_\tau$, $m_s = \frac{1}{3} m_\mu$ and
$m_dm_s = m_e m_\mu$ all hold to a good approximation. Depending on $\nu_\mu
\leftrightarrow \nu_\tau$ mixing which can even be maximal, the mixing angle
relevant for solar neutrino oscillation lies in the range $7.8 \times 10^{-3}
\stackrel{_<}{_\sim} \sin^2 2\theta_{e\mu} \stackrel{_<}{_\sim} 2.1 \times
10^{-2}$. For the $^{71}$Ga experiment the event rate, normalized against the
standard solar model prediction of 132 SNU, is estimated to be between 80 and
20 SNU.
|
hep-ph/9209214
| 727,445 |
We show that minimal SO(10) Grand Unification models where the fermions have
Yukawa couplings to only one (complex) {\bf 10} and one {\bf 126} of Higgs
scalars lead to a very predictive neutrino spectrum. This comes about since the
standard model doublet contained in the {\bf 126} of Higgs (needed for the
see--saw mechanism) receives an induced vacuum expectation value at
tree--level, which, in addition to correcting the bad asymptotic mass relations
$m_d=m_e$ and $m_s=m_\mu$, also relates the Majorana neutrino mass matrix to
observables in the charged fermion sectors. We find that (i) the
$\nu_e-\nu_{\mu}$ mixing angle relevant for the solar neutrinos can be
considerably smaller than the Cabibbo angle and lies in the range ${\rm
sin}\theta_{e \mu}= 0-0.3$, (ii) $\nu_e-\nu_\tau$ mixing is sin$\theta_{e \tau}
\simeq 3|V_{td}| \simeq 0.05$, (iii) the $\nu_\mu-\nu_\tau$ mixing angle is
large, ${\rm sin}\theta_{\mu \tau} \simeq 3|V_{cb}|=0.12-0.16$, and (iv)
$m_{\nu_\tau}/m_{\nu_\mu} \ge 10^3$, implying that $\nu_{\mu}-\nu_\tau$
oscillations should be accessible to forthcoming experiments.
|
hep-ph/9209215
| 727,445 |
The use of neural networks for signal vs.~background discrimination in
high-energy physics experiment has been investigated and has compared favorably
with the efficiency of traditional kinematic cuts. Recent work in top quark
identification produced a neural network that, for a given top quark mass,
yielded a higher signal to background ratio in Monte Carlo simulation than a
corresponding set of conventional cuts. In this article we discuss another
pattern-recognition algorithm, the binary decision tree. We have applied a
binary decision tree to top quark identification at the Tevatron and found it
to be comparable in performance to the neural network. Furthermore,
reservations about the "black box" nature of neural network discriminators do
not apply to binary decision trees; a binary decision tree may be reduced to a
set of kinematic cuts subject to conventional error analysis.
|
hep-ph/9209216
| 727,445 |
High temperature series expansions of the spin-spin correlation function for
the plane rotator (or XY) model on the square lattice are extended by three
terms through order $\beta^{20}$. Tables of the expansion coefficients are
reported for the correlation function spherical moments of order $l=0,1,2$. The
expansion coefficients through $\beta^{15}$ for the vorticity are also
tabulated. Our analysis of the series supports the Kosterlitz-Thouless
predictions on the structure of the critical singularities and leads to fairly
accurate estimates of the critical parameters.
|
hep-lat/9209011
| 727,445 |
We analyze the allowed spectrum of electric and magnetic charges carried by
dyons in (toroidally compactified) heterotic string theory in four dimensions
at arbitrary values of the string coupling constant and $\theta$ angle. The
spectrum is shown to be invariant under electric-magnetic duality
transformation, thereby providing support to the conjecture that this is an
exact symmetry in string theory.
|
hep-th/9209016
| 727,446 |
An on-shell formulation of (p,q), 2\leq p \leq 4, 0\leq q\leq 4,
supersymmetric coset models with target space the group G and gauge group a
subgroup H of G is given. It is shown that there is a correspondence between
the number of supersymmetries of a coset model and the geometry of the coset
space G/H. The algebras of currents of supersymmetric coset models are
superconformal algebras. In particular, the algebras of currents of (2,2) and
(4,0) supersymmetric coset models are related to the N=2 Kazama-Suzuki and N=4
Van Proeyen superconformal algebras correspondingly.
|
hep-th/9209017
| 727,446 |
One of the interesting aspects of the CuO superconductors is that
superconductivity is happening so close to the antiferromagnetic state. The
nuclear magnetic resonance and the recent neutron scattering experiments
clearly indicate that magnetic correlations persist in to the heavily doped
regime. In this paper we will discuss some of the details of the coupling of
the nuclear magnetic spin to the conduction electron spins. Furthermore we will
show that a simple band structure can explain the recent neutron scattering
data in the \LaSrCuO material for the optimal concentration of $x\approx 0.15$
if the lifetime effects are included.
|
cond-mat/9209005
| 727,446 |
A magnetic susceptibility which decreases with decreasing temperature is
observed in all $CuO_2$ based superconductors with less than optimal doping. We
propose that in $La_{2-x} Sr_x CuO_4$ this is due to antiferromagnetic ordering
which is prevented by the low spatial dimensionality while in $YBa_2 Cu_3
O_{6.6}$ it is due to the interplay between antiferromagnetic fluctuations
within a plane and singlet pairing of electrons between nearest neighbor
planes.
|
cond-mat/9209006
| 727,446 |
The construction of mirror symmetry in the heterotic string is reviewed in
the context of Calabi-Yau and Landau-Ginzburg compactifications. This framework
has the virtue of providing a large subspace of the configuration space of the
heterotic string, probing its structure far beyond the present reaches of
solvable models. The construction proceeds in two stages: First all
singularities/catastrophes which lead to ground states of the heterotic string
are found. It is then shown that not all ground states described in this way
are independent but that certain classes of these LG/CY string vacua can be
related to other, simpler, theories via a process involving fractional
transformations of the order parameters as well as orbifolding. This
construction has far reaching consequences. Firstly it allows for a systematic
identification of mirror pairs that appear abundantly in this class of string
vacua, thereby showing that the emerging mirror symmetry is not accidental.
This is important because models with mirror flipped spectra are a priori
independent theories, described by distinct CY/LG models. It also shows that
mirror symmetry is not restricted to the space of string vacua described by
theories based on Fermat potentials (corresponding to minimal tensor models).
Furthermore it shows the need for a better set of coordinates of the
configuration space or else the structure of this space will remain obscure.
While the space of LG vacua is {\it not} completely mirror symmetric, results
described in the last part suggest that the space of Landau--Ginburg {\it
orbifolds} possesses this symmetry.
|
hep-th/9209018
| 727,447 |
A comparative investigation of various Pomeron models is carried out through
the study of their predicted values of $ \sigma_{tot}$, B, and
$\frac{\sigma_{el}}{\sigma_{tot}}$ in high energy pp and p$\bar{p}$ scattering.
Our results strongly support a picture of the Pomeron in which we have both
moderate blackening and expansion of the p($\bar{p}$) - p amplitude in impact
parameter space as a function of energy in the ISR-SSC domain. In particular,
we obtain an excellent reproduction of the data with a hybrid eikonal model
which combines the hard Lipatov-like QCD Pomeron with the old fashioned soft
Pomeron and Regge terms. Our analysis shows that the additive quark model, at
least in the naive form, is not compatible with the data.
|
hep-ph/9209218
| 727,448 |
We study the one component $\Phi^4$ model for four different lattice actions
in the Gaussian limit and for the Ising model in the broken phase. Emphasis is
put on the euclidean invariance properties of the boson propagator. A measure
of the violation of rotational symmetry serves as a tool to compare the
regularization dependence of the triviality bound.
|
hep-lat/9209012
| 727,448 |
We compute properties of the interface of the 3-dimensional Ising model for a
wide range of temperatures, covering the whole region from the low temperature
domain through the roughening transition to the bulk critical point. The
interface tension sigma is obtained by integrating the surface energy density
over the inverse temperature beta. We use lattices of size L x L x T, with L up
to 64, and T up to 27. The simulations with antiperiodic boundary conditions in
T-direction are done with the Hasenbusch-Meyer interface cluster algorithm that
turns out to be very efficient. We demonstrate that in the rough phase the
large distance behavior of the interface is well described by a massless
Gaussian dynamics. The surface stiffness coefficient kappa is determined. We
also attempt to determine the correlation length xi and study universal
quantities like xi^2 * sigma and xi^2 * kappa. Results for the interfacial
width on lattices up to 512 x 512 x 27 are also presented.
|
hep-lat/9209013
| 727,448 |
First order QCD and leading QED corrections to Higgs boson production in the
channel $e^-p \to \nu H^0 X; H^0 \to b\bar{b}$ are calculated for the
kinematical conditions at LEP $\otimes$ LHC ($\sqrt{s} = 1360 \GeV$) and the
interesting mass range $80 < M_H < 150 \GeV$. In the DIS scheme the QCD
corrections (not including the corrections to the branching ratio, which are
well-known) are found to be about 1\% for the total cross section and $-13\%$
to $-10\%$ for the observable cross section as defined by appropriate cuts. The
latter results depend on the definition of these cuts. The QED corrections
amount to about $-5\%$. Also obtainable with anonymous ftp from
gluon.hep.physik.uni-muenchen.de.
|
hep-ph/9209219
| 727,448 |
We present the results of an extensive exploration of the five-dimensional
parameter space of the minimal $SU(5)$ supergravity model, including the
constraints of a long enough proton lifetime ($\tau_p>1\times10^{32}\y$) and a
small enough neutralino cosmological relic density ($\Omega_\chi h^2_0\le1$).
We find that the combined effect of these two constraints is quite severe,
although still leaving a small region of parameter space with $m_{\tilde
g,\tilde q}<1\TeV$. The allowed values of the proton lifetime extend up to
$\tau_p\approx1\times10^{33}\y$ and should be fully explored by the
SuperKamiokande experiment. The proton lifetime cut also entails the following
mass correlations and bounds: $m_h\lsim100\GeV$,
$m_\chi\approx{1\over2}m_{\chi^0_2}\approx0.15\gluino$, $m_{\chi^0_2}\approx
m_{\chi^+_1}$, and $m_\chi<85\,(115)\GeV$,
$m_{\chi^0_2,\chi^+_1}<165\,(225)\GeV$ for $\alpha_3=0.113\,(0.120)$. Finally,
the {\it combined} proton decay and cosmology constraints predict that if
$m_h\gsim75\,(80)\GeV$ then $m_{\chi^+_1}\lsim90\,(110)\GeV$ for
$\alpha_3=0.113\,(0.120)$. Thus, if this model is correct, at least one of
these particles will likely be observed at LEPII.
|
hep-ph/9209220
| 727,448 |
Open superstrings at non-zero temperature are considered. A novel
representation for the free energy (Laurent series representation) is
constructed. It is shown that the Hagedorn temperature arises in this formalism
as the convergence condition (specifically, the radius of convergence) of the
Laurent series.
|
hep-th/9209021
| 727,448 |
We consider algebras with one binary operation $\cdot$ and one generator
({\it monogenic}) and satisfying the left distributive law $a\cdot (b\cdot
c)=(a\cdot b)\cdot (a\cdot c)$. One can define a sequence of finite
left-distributive algebras $A_n$, and then take a limit to get an infinite
monogenic left-distributive algebra~$A_\infty$. Results of Laver and Steel
assuming a strong large cardinal axiom imply that $A_\infty$ is free; it is
open whether the freeness of $A_\infty$ can be proved without the large
cardinal assumption, or even in Peano arithmetic. The main result of this paper
is the equivalence of this problem with the existence of a certain algebra of
increasing functions on natural numbers, called an {\it embedding algebra}.
Using this and results of the first author, we conclude that the freeness of
$A_\infty$ is unprovable in primitive recursive arithmetic.
|
math/9209202
| 727,449 |
Let P be the direct product of countably many copies of the additive group Z
of integers. We study, from a set-theoretic point of view, those subgroups of P
for which all homomorphisms to Z annihilate all but finitely many of the
standard unit vectors. Specifically, we relate the smallest possible size of
such a subgroup to several of the standard cardinal characteristics of the
continuum. We also study some related properties and cardinals, both
group-theoretic and set-theoretic. One of the set-theoretic properties and the
associated cardinal are combinatorially natural, independently of any
connection with algebra.
|
math/9209203
| 727,449 |
A model of $CuO_2$ planes weakly doped with partially delocalised holes is
considered. The effect of such a hole on the background AFM spin texture can be
represented by a purely magnetic Hamiltonian $H = - \sum_{(ijk)} (\vec S_i
\cdot \vec S_j \times \vec S_k)^2$, where the summation is over the four
triangles of a single plaquette. We show that this model of randomly
distributed chiral spin defects leads to an in--plane spin correlation length
approximately described by $\xi^{-1} (x,T) = \xi^{-1} (0,T) + \xi^{-1} (x,0)$,
consistent with neutron scattering experiments on $La_{2-x}Sr_xCuO_4$. Further,
this model leads to favourable comparisons with $B_{1g}$ Raman scattering
results for the same cuprate system.
|
cond-mat/9209007
| 727,449 |
Two dimensional quantum gravity coupled to a conformally invariant matter
field of central charge c=n/2, is represented, in a discretized version, by n
independent Ising spins per cell of the triangulations of a random surface. The
matrix integral representation of this model leads to a diagrammatic expansion
at large orders, when the Ising coupling constant is tuned to criticality, one
extracts the values of the string susceptibility exponent. We extend our
previous calculation to order eight for genus zero and investigate now also the
genus one case in order to check the possibility of having a well-defined
double scaling limit even c>1.
|
hep-th/9209022
| 727,449 |
The first quantum mass corrections for the solitons of complex $sl(n)$ affine
Toda field theory are calculated. The corrections are real and preserve the
classical mass ratios. The formalism also proves that the solitons are
classically stable.
|
hep-th/9209024
| 727,449 |
Canonical transformations relating the variables of the ADM-, Ashtekar's and
Witten's formulations of gravity are computed in 2+1~dimensions. Three
different forms of the BRST-charge are given in the 2+1 dimensional Ashtekar
formalism, two of them using Ashtekar's form of the constraints and one of them
using the forms suggested by Witten. The BRST-charges are of different rank.
|
gr-qc/9209003
| 727,449 |
We present a mean-field calculation of the phase diagram of a simple model of
localized moments, in the hexagonal uranium heavy-fermion compounds. The model
considers a non-Kramers quadrupolar doublet ground state magnetically coupled
with a singlet excited-state, favoring in-plane van-Vleck magnetism, as has
been conjectured for UPt$_3$. The Hamiltonian which defines the model is
Heisenberg like in both, magnetic and quadrupolar moments. Among our main
results are: (i) for zero intersite quadrupolar coupling, the magnetic order is
achieved by a first order transition above a critical intersite magnetic
coupling value which becomes second order at higher coupling strengths. (ii)
for finite intersite quadrupolar coupling, at temperatures below a second order
quadrupolar ordering transition, the minimal magnetic coupling value is
increased but (a) the magnetic ordering temperature is enhanced above this
value, and (b) the ordering of first and second order transitions in the phase
diagram is reversed.
|
cond-mat/9209008
| 727,449 |
In this paper we study conditions on a Banach space X that ensure that the
Banach algebra K(X) of compact operators is amenable. We give a symmetrized
approximation property of X which is proved to be such a condition. This
property is satisfied by a wide range of Banach spaces including all the
classical spaces. We then investigate which constructions of new Banach spaces
from old ones preserve the property of carrying amenable algebras of compact
operators. Roughly speaking, dual spaces, predual spaces and certain tensor
products do inherit this property and direct sums do not. For direct sums this
question is closely related to factorization of linear operators. In the final
section we discuss some open questions, in particular, the converse problem of
what properties of X are implied by the amenability of K(X).
|
math/9209211
| 727,449 |
We discuss states in the meson spectrum which have explicit gluonic
components. Glueballs (with no valence quarks) and hybrid mesons (with valence
quarks) are both reviewed. We present in some detail lattice simulation
results. ( to appear in proceedings of QCD-20 years, Aachen Workshop)
|
hep-lat/9209014
| 727,449 |
We propose a bilocal field theory for mesons in two dimensions obtained as a
kind of non local bosonization of two dimensional QCD. Its semi-classical
expansion is equivalent to the $1/N_c$ expansion of QCD. Using an ansatz we
reduce the classical equation of motion of this theory in the baryon number one
sector to a relativistic Hartree equation and solve it numerically. This (non
topological) soliton is identified with the baryon.
|
hep-th/9209027
| 727,449 |
We study the dressing of operators and flows of corresponding couplings in
models of {\it embedded} random surfaces. We show that these dressings can be
obtained by applying the methods of David and Distler and Kawai. We consider
two extreme limits. In the first limit the string tension is large and the
dynamics is dominated by the Nambu-Goto term. We analyze this theory around a
classical solution in the situation where the length scale of the solution is
large compared to the length scale set by the string tension. Couplings get
dressed by the liouville mode (which is now a composite field) in a non-trivial
fashion. However this does {\it not} imply that the excitations around a
physical ``long string" have a phase space corresponding to an extra dimension.
In the second limit the string tension is small and the dynamics is governed by
the extrinsic curvature term. We show, perturbatively, that in this theory the
relationship between the induced metric and the worldsheet metric is
``renormalized", while the extrinsic curvature term receives a non-trivial
dressing as well. This has the consequence that in a generic situation the
dependence of couplings on the physical scale is different from that predicted
by their beta functions.
|
hep-th/9209025
| 727,449 |
We show explicitly that the question of gauge invariance of the effective
potential in standard scalar electrodynamics remains unchanged despite the
introduction of the Chern-Simons term. The result does not depend on the
presence of the Maxwell term in the Chern-Simons territory.
|
hep-th/9209026
| 727,449 |
In a somewhat overlooked work by Seiberg, a definition of the topological
charge for SU(N) lattice fields was given. Here, it is shown that Seibergs and
L\"{u}schers charge definition are related up to the section of the bundle.
With the continued interest in baryon number violating processes, Seibergs
paper is useful since it allows for a Chern-Simons number also.
|
hep-lat/9209015
| 727,450 |
In this paper we consider the representation theory of N=1 Super-W-algebras
with two generators for conformal dimension of the additional superprimary
field between two and six. In the superminimal case our results coincide with
the expectation from the ADE-classification. For the parabolic algebras we find
a finite number of highest weight representations and an effective central
charge $\tilde c = 3/2$. Furthermore we show that most of the exceptional
algebras lead to new rational models with $\tilde c > 3/2$. The remaining
exceptional cases show a new `mixed' structure. Besides a continuous branch of
representations discrete values of the highest weight exist, too.
|
hep-th/9209030
| 727,450 |
We give a general procedure for extracting the propagators in gauge theories
in presence of a sharp gauge fixing and we apply it to derive the propagators
in quantum gravity in the radial gauge, both in the first and in the second
order formalism in any space-time dimension. In the three dimensional case such
propagators vanish except for singular collinear contributions, in agreement
with the absence of propagating gravitons.
|
hep-th/9209028
| 727,450 |
We discuss several issues regarding analyses which use loop calculations to
put constraints on anomalous trilinear gauge boson couplings (TGC's). Many such
analyses give far too stringent bounds. This is independent of questions of
gauge invariance, contrary to the recent claims of de Rujula et. al., since the
lagrangians used in these calculations ARE gauge invariant, but the SU(2)_L X
U(1)_Y symmetry is nonlinearly realized. The real source of the problem is the
incorrect use of cutoffs -- the cutoff dependence of a loop integral does not
necessarily reflect the true dependence on the heavy physics scale M. If done
carefully, one finds that the constraints on anomalous TGC's are much weaker.
We also compare effective lagrangians in which SU(2)_L X U(1)_Y is realized
linearly and nonlinearly, and discuss the role of custodial SU(2) in each
formulation.
|
hep-ph/9209222
| 727,450 |
Let $F:[0,T]\times\R^n\mapsto 2^{\R^n}$ be a continuous multifunction with
compact, not necessarily convex values. In this paper, we prove that, if $F$
satisfies the following Lipschitz Selection Property: \begin{itemize}
\item[{(LSP)}] {\sl For every $t,x$, every $y\in \overline{co} F(t,x)$ and
$\varepsilon>0$, there exists a Lipschitz selection $\phi$ of $\overline{co}F$,
defined on a neighborhood of $(t,x)$, with $|\phi(t,x)-y|<\varepsilon$.}
\end{itemize} then there exists a measurable selection $f$ of $ext F$\ such
that, for every $x_0$, the Cauchy problem $$ \dot x(t)=f(t,x(t)),\qquad\qquad
x(0)=x_0 $$ has a unique Caratheodory solution, depending continuously on
$x_0$. We remark that every Lipschitz multifunction with compact values
satisfies (LSP). Another interesting class, for which (LSP) holds, consists of
those continuous multifunctions $F$ whose values are compact and have convex
closure with nonempty interior.
|
funct-an/9209001
| 727,450 |
We study a new class of flavor changing interactions, which can arise in
models based on extended gauge groups (rank $>$4) when new charged fermions are
present together with a new neutral gauge boson. We discuss the cases in which
the flavor changing couplings in the new neutral current coupled to the
$Z^\prime$ are theoretically expected to be large, implying that the observed
suppression of neutral flavor changing transitions must be provided by heavy
$Z^\prime$ masses together with small $Z$-$Z^\prime$ mixing angles.
Concentrating on E$_6$ models, we show how the tight experimental limit on $\mu
\rightarrow eee$ implies serious constraints on the $Z^\prime$ mass and mixing
angle. We conclude that if the value of the flavor changing parameters is
assumed to lie in a theoretically natural range, in most cases the presence of
a $Z^\prime$ much lighter than 1 TeV is unlikely.
|
hep-ph/9209223
| 727,450 |
We prove that $\mu=\mu^{<\mu}$, $2^\mu=\mu^+$ and ``there is a non reflecting
stationary subset of $\mu^+$ composed of ordinals of cofinality $<\mu$'' imply
that there is a $\mu$-complete Souslin tree on $\mu^+$.
|
math/9209204
| 727,451 |
I present a cluster Monte Carlo algorithm that gives direct access to the
interface free energy of Ising models. The basic idea is to simulate an
ensemble that consists of both configurations with periodic and with
antiperiodic boundary conditions. A cluster algorithm is provided that
efficently updates this joint ensemble. The interface tension is obtained from
the ratio of configurations with periodic and antiperiodic boundary conditions,
respectively. The method is tested for the 3-dimensional Ising model.
|
hep-lat/9209016
| 727,451 |
The formalism of non-commutative geometry of A. Connes is used to construct
models in particle physics. The physical space-time is taken to be a product of
a continuous four-manifold by a discrete set of points. The treatment of Connes
is modified in such a way that the basic algebra is defined over the space of
matrices, and the breaking mechanism is planted in the Dirac operator. This
mechanism is then applied to three examples. In the first example the discrete
space consists of two points, and the two algebras are taken respectively to be
those of $2\times 2$ and $1\times 1$ matrices. With the Dirac operator
containing the vacuum breaking $SU(2)\times U(1)$ to $U(1)$, the model is shown
to correspond to the standard model. In the second example the discrete space
has three points, two of the algebras are identical and consist of $5\times 5$
complex matrices, and the third algebra consists of functions. With an
appropriate Dirac operator this model is almost identical to the minimal
$SU(5)$ model of Georgi and Glashow. The third and final example is the
left-right symmetric model $SU(2)_L\times SU(2)_R\times U(1)_{B-L}.$
|
hep-ph/9209224
| 727,451 |
In this note we investigate some aspects of the local structure of finite
dimensional $p$-Banach spaces. The well known theorem of Gluskin gives a sharp
lower bound of the diameter of the Minkowski compactum. In [Gl] it is proved
that diam$({\cal M}_n^1)\geq cn$ for some absolute constant $c$. Our purpose is
to study this problem in the $p$-convex setting. In [Pe], T. Peck gave an upper
bound of the diameter of ${\cal M}_n^p$, the class of all $n$-dimensional
$p$-normed spaces, namely, diam$({\cal M}_n^p)\leq n^{2/p-1}$. We will show
that such bound is optimum.
|
math/9209213
| 727,451 |
We study a theory of Dirac fermions on a disk in presence of an
electromagnetic field. Using the heat-kernel technique we compute the
functional determinant which results after decoupling the zero-flux gauge
degrees of freedom from the fermions. We also compute the Green functions of
the remaining fermionic theory with the appropriate boundary conditions.
Finally we analyze the coset model associated to this gauge theory and compute
all its correlations functions.
|
hep-th/9209038
| 727,451 |
We calculate exactly the rate of pair production of open bosonic and
supersymmetric strings in a constant electric field. The rate agrees with
Schwinger's classic result in the weak-field limit, but diverges when the
electric field approaches some critical value of the order of the string
tension. (Phyzzx file)
|
hep-th/9209032
| 727,451 |
In [1,2] we established and discussed the algebra of observables for 2+1
gravity at both the classical and quantum level. Here our treatment broadens
and extends previous results to any genus $g$ with a systematic discussion of
the centre of the algebra. The reduction of the number of independent
observables to $6g-6 (g > 1)$ is treated in detail with a precise
classification for $g = 1$ and $g = 2$.
|
hep-th/9209031
| 727,451 |
The lensing effect of curved space, which can cause the angular diameter of a
fixed reference length seen on the sky to reach a minimum and then increase
with redshift, depends sensitively on the value of the cosmological constant,
$\Lambda$, in a flat universe. The redshift of an observed minimum and the
asymptotic slope can in principle provide strong constraints on $\Lambda$. The
sensitivity to a non-zero cosmological constant in a flat universe is compared
to the sensitivity to $q_0$ in an open universe without a cosmological
constant, and to inherent ambiguities due to uncertainties in distance measures
and the possible effects of evolution. If evolutionary uncertainties can be
overcome, the reported observations of the angular diameter of compact radio
jets as a function of redshift, which appear to exhibit such a minimum, could
provide the strongest available limit on the cosmological constant in a flat
universe, and on $\Omega$ in an open universe.
|
hep-ph/9209225
| 727,451 |
New non-perturbative interactions in the effective action of two dimensional
string theory are described. These interactions are due to ``stringy"
instantons
|
hep-th/9209033
| 727,451 |
We discuss various techniques for computing the semi-infinite cohomology of
highest weight modules which arise in the BRST quantization of two dimensional
field theories. In particular, we concentrate on two such theories -- the $G/H$
coset models and $2d$ gravity coupled to $c\leq 1$ conformal matter. (to appear
in the proceedings of the XXV Karpacz Winter School)
|
hep-th/9209034
| 727,452 |
In this paper we discuss the BRST-quantization of anomalous 2d-Yang Mills
(YM) theory. Since we use an oscillator basis for the YM-Fock-space the anomaly
appears already for a pure YM-system and the constraints form a Kac-Moody
algebra with negative central charge. We also discuss the coupling of chiral
fermions and find that the BRST-cohomology for systems with chiral fermions in
a sufficiently large representation of the gauge group is completely equivalent
to the cohomology of the finite dimensional gauge group. For pure YM theory or
YM theory coupled to chiral fermions in small representations there exists an
infinite number of inequivalent cohomology classes. This is discussed in some
detail for the example of $SU(2)$.
|
hep-th/9209035
| 727,452 |
The Cosmological Principle states that the universe is both homogeneous and
isotropic. This, alone, is not enough to specify the global geometry of the
spacetime. If we were able to measure both the Hubble constant and the energy
density we could determine whether the universe is open or closed.
Unfortunately, while some agreement exists on the value of the Hubble constant,
the question of the energy density seems quite intractable. This Letter
describes a possible way of avoiding this difficulty and shows that if one
could measure the rate at which light-rays emerging from a surface expand, one
might well be able to deduce whether the universe is closed.
|
gr-qc/9209004
| 727,452 |
The existance of a spin disordered ground state for the frustrated Quantum
Heisenberg Antiferromagnet on a square lattice is reconsidered. It is argued
that there is a unique action which is continuous through the whole phase
diagram, except at the Lifshitz point, so that the Neel and helicoidal states
can not coexist and there has to be an intermediate spin liquid state. To show
it, a detailed study combining Spin-Wave theory, Schwinger Bosons Mean Field
Theory and a scaling analysis of the appropriate hydrodynamic action is
performed. When done carefully, all these theories agree and strongly support
the existance of the spin liquThe manuscript has eight figures, which are
available upon request to the author. e-mail address is
[email protected]
|
cond-mat/9209009
| 727,452 |
We study the 3d effective theory of the high T Abelian Higgs model with N
real scalars and gauge and scalar couplings denoted g and $\lambda$,
respectively. We find for the three cases a) $6g^2/\lambda =0(1)$, b)
$6g^2/\lambda=0(N)$ and c) $6g^2/\lambda=O(N^{2\over3})$ the following results:
a) The O(N)+O(1) potential admits only a second order phase transition, b) The
O(1) potential admits a first order transition and c) the O(N^{1\over3}) +O(1)
result gives a first order transition whose strength diminshes with N.
|
hep-ph/9209227
| 727,452 |
The Maxwell vector potential and the Dirac spinor used to describe the
classical theory of electrodynamics both have components which are considered
to be ordinary smooth functions on space-time. We reformulate electrodynamics
by adding an additional structure to the algebra of these functions in the form
of the algebra $M_n$ of $n \times n$ complex matrices. This involves a
generalization of the notions of geometry to include the geometry of matrices.
Some rather general constraints on the reformulation are imposed which can be
motivated by considering matrix geometry in the limit of very large $n$. A few
of the properties of the resulting models are given for the values $n=2,3$. One
of the more interesting is the existence of several distinct stable phases or
vacua. The fermions can be quark-like in one and lepton-like in another.
|
hep-ph/9209226
| 727,452 |
We present the minimal sextet--quark condensation model as an attractive
alternative to the standard model. The model is constructed by a simple and
natural extension beyond the standard model and has many new interesting
features some of which can be tested readily at the existing colliders. A
crucial test may be a short--lived axion-- like $\eta_6$ of mass 30--60 GeV,
which can produce high energy photons diffractively at hadron colliders and
radiatively in $e^+ e^-$ colliders.
|
hep-ph/9209228
| 727,452 |
We derive the recently proposed BRST charge for non-critical W strings from a
Lagragian approach. The basic observation is that, despite appearances, the
combination of two classical ``matter'' and ``Toda'' w_3 systems leads to a
closed modified gauge algebra, which is of the so-called soft type. Based on
these observations, a novel way to construct critical W_3 strings is given.
|
hep-th/9209037
| 727,452 |
We study a model for anisotropic singlet pairing in $A_3{\rm C}_{60}$, using
a realistic model for the Fermi surface in a hypothesized
orientationally-ordered doped crystal. Anisotropic solutions are studied by
combining numerical solutions to the gap equation in the low-temperature phase
with a Landau expansion near the mean field critical temperature. We focus on a
class of three-dimensional nodeless $d$-wave solutions to the model, which
exhibit a fully developed gap everywhere on the Fermi surface, but non-BCS
temperature dependence of the order parameter in the condensed state, a
relatively large value of the low-temperature gap, $2\Delta/kT_{\rm c}$ , and
non-BCS structure in the quasiparticle spectrum near the gap.
|
cond-mat/9209011
| 727,452 |
We investigate quantum mechanical Hamiltonians with explicit time dependence.
We find a class of models in which an analogue of the time independent \S
equation exists. Among the models in this class is a new exactly soluble model,
the harmonic oscillator with frequency inversely proportional to time.
|
hep-th/9209039
| 727,452 |
Hadron bubbles that nucleate with radius $R_{nuc}$ in a quark sea (if the
phase transition is first order) are shown to be unstable to the growth of
nonspherical structure when the bubble radii exceed a critical size of $20 -
10^3$ $R_{nuc}$. This instability is driven by a very thin layer of slowly
diffusing excess baryon number that forms on the surface of the bubble wall and
limits its growth. This instability occurs on a shorter length scale than those
studied previously and these effects can thus be important for both cosmology
and heavy ion collisions.
|
hep-ph/9209229
| 727,452 |
We use the single-cluster Monte Carlo update algorithm to simulate the
three-dimensional classical Heisenberg model in the critical region on simple
cubic lattices of size $L^3$ with $L=12, 16, 20, 24, 32, 40$, and $48$. By
means of finite-size scaling analyses we compute high-precision estimates of
the critical temperature and the critical exponents, using extensively
histogram reweighting and optimization techniques. Measurements of the
autocorrelation time show the expected reduction of critical slowing down at
the phase transition. This allows simulations on significantly larger lattices
than in previous studies and consequently a better control over systematic
errors in finite-size scaling analyses.
|
hep-lat/9209017
| 727,452 |
We show how to construct a complete set of eigenstates of the hamiltonian of
the one-dimensional Hubbard model on a lattice of even length $L$. This is done
by using the nested Bethe Ansatz {\it and} the $SO(4)$ symmetry of the model.
We discuss in detail how the counting of independent eigenstates is carried
out.
|
cond-mat/9209012
| 727,453 |
Reanalysis of Einstein IPC data and new observations from the GINGA
LAC indicate the presence of extended X-ray emission (10-50 kpc) around the
starburst galaxy M82. Here we model this emission by calculating numerical
hydrodynamic simulations of the starburst event to much later times and larger
scales than previously considered. For our models, we adopt a supernova rate of
0.1 ${\rm yr}^{-1}$, and an extended low-density static halo that is bound to
the galaxy. There are three stages to the evolution of the wind-blown bubble
and the propagation of the shock front: the bubble expands in an almost uniform
density disk gas, with a deceleration of the shock front ($t \alt $ 3.6 Myr);
breakout from the disk and the upward acceleration of the shock front (3.6
Myr $\alt t \alt$ 18 Myr); propagation into the halo, leading to a more
spherical system and shock deceleration (18 Myr $\alt t$). For a halo density
of $10^{-3} {\rm cm}^{-3}$, the outflow reaches a distance of 40-50 kpc from
the center of the starburst galaxy in 50 Myr. We calculate the time evolution
of the X-ray luminosity and find that the extended starburst emits $3\times
10^{39}\lcgs$ to $10^{40}\lcgs$ in the
GINGA LAC band and $\sim 10^{41}\lcgs$ in the Einstein or ROSAT
HRI band. The degree of the ionization equilibrium in the outflow and its
effect on the iron K$\alpha$ line emission are discussed.
|
astro-ph/9209002
| 727,453 |
We consider luminescence in photo-excited neutral C_60 using the
Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the
luminescence we use a collective coordinate method where our collective
coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon
mode and extrapolates between the ground state "dimerisation" and the exciton
polaron. There is good agreement for the existing luminescence peak spacing and
fair agreement for the relative intensity. We predict the existence of further
peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn,
36.90+f
|
cond-mat/9209013
| 727,454 |
In a recent paper, we suggested that the density fluctuation spectra arising
from power-law (or extended) inflation, which are tilted with respect to the
Harrison--Zel'dovich spectrum, may provide an explanation for the excess large
scale clustering seen in galaxy surveys such as the APM survey. In the light of
the new results from COBE, we examine in detail here cold dark matter
cosmogonies based on inflationary models predicting power-law spectra. Along
with power-law and extended inflation, this class includes natural inflation.
The latter is of interest because, unlike the first two, it produces a
power-law spectrum without significant gravitational wave production. We
examine a range of phenomena, including large angle microwave background
fluctuations, clustering in the galaxy distribution, bulk peculiar velocity
flows, the formation of high redshift quasars and the epoch of structure
formation. Of the three models, only natural inflation seems capable of
explaining the large scale clustering of optical galaxies. Such a model, though
at best marginal even at present, has some advantages over standard CDM and on
most grounds appears to perform at least as well. Power-law inflation's primary
interest may ultimately only be in permitting a larger bias parameter than
standard CDM; it appears unable to explain excess clustering. Most models of
extended inflation are ruled out at a high confidence level.
|
astro-ph/9209003
| 727,454 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.