will face difficulties to discriminate between the different Higgs states and to determine their masses. This is especially true in the so-called “intense coupling limit”, $m_h\sim m_A\sim m_H\sim {\cal
O}(100~\GeV)$ [@EB]. As a specific example we calculate the event rates for the exclusive central production of mass $115~\GeV$ $0^\pm$ bosons at the LHC.

Exclusive diffractive production: general rules {#sec:2}
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Here we study the general rules for the amplitudes of the exclusive diffractive process 1+2  3+h+4, \[eq:adder\] shown in Fig. \[fig:1\], where $1,\dots,4$ are hadrons, and where the centrally produced particle $h$ has spin and parity $J^P$. We show that the production process has characteristic features, that depend on the value of $J^P$, which follow from general principles.

To begin, we assume that all the particles are spinless. Then, at high energies and small momentum transfer,

[l @ l]{} s\_1 = (p\_3+p\_h)\^2 s\_0, & s\_2 = (p\_4 + p\_h)\^2 s\_0\
t\_1-p\_[3]{}\^2 s\_0, & t\_2 -p\_[4]{}\^2 s\_0, \[eq:bear\]

the amplitude can be written in the form [@a1] T\_[12]{}\^[3h4]{}(s\_1,s\_2,p\_[3]{}, p\_[4]{}) = \_[i,k]{} g\_[13]{}(t\_1)g\_[24]{}(t\_2)()\^[\_i(t\_1)]{}()\^[\_k(t\_2)]{} (\_i(t\_1))(\_k(t\_2)) g\_[ik]{}\^h(t\_1,t\_2,), \[eq:cat\] where $s_0 = 1~\GeV^2$, $\phi$ is the angle between the transverse momenta $\vec p_{3\perp}$ and $\vec p_{4\perp}$ of the outgoing protons and (\_i(t)) = -() \[eq:dog\] 