arXiv subjects
Publications and source records attributed to R. Fiore.
The scattering amplitude in the dual model with Mandelstam analyticity and trajectory $α(s)=α_{0}-γ\ln [ (1+β\sqrt{s_{0} -s})/(1+ β\sqrt{s_{0}})]$ is studied in the limit $s,|t|\to \infty, s/t=const.$ By using the saddle point method, a series decomposition for the scattering amplitude is obtained, with the leading and two sub-leading terms calculated explicitly.
Hadron diffraction dissociation is considered in the dipole Pomeron model where the Pomeron is represented by a double pole in the J-plane. We find that unitarity is satisfied without decoupling of the triple Pomeron vertex. The reaction bar{p}+p --> bar{p}+X is analysed.
Exclusive diffractive photoproduction of heavy vector mesons (V=phi, J/psi and Upsilon) at HERA is studied in a model employing a dipole Pomeron exchange (P) with an inelastic gamma-P-V vertex. The model is fitted to the data on dsigma/dt, B and elastic sigma for Q^2=0 and beyond the threshold region. The elastic cross sections for both phi and J/psi photoproduction show a moderate increase within the HERA energy region. The flattening of the slope B(s) (little or no shrinkage) for J/psi is not correlated with the slope of the Pomeron trajectory. Estimates for Upsilon photoproduction at HERA are given.
The broken-symmetry electroweak vacuum is destabilized in the presence of a magnetic field stronger than a critical value. Such magnetic field may be generated in the phase transition and restore the symmetry inside the bubbles. A numerical calculation indicates that the first-order phase transition is delayed but may be completed for a sufficient low value of the Higgs mass unless the magnetic field is extremely high.
The generalization of the BFKL equation for the case of non-forward scattering is considered. The kernel of the generalized equation in the next-to-leading approximation is expressed in terms of the gluon Regge trajectory and the effective vertices for particle production in Reggeon collisions. The ``bootstrap'' equations for the gluon Reggeization are presented.
According to the Svetitsky-Yaffe conjecture, a three-dimensional gauge theory undergoing a continuous deconfinement transition is in the same universality class as a two-dimensional statistical model with order parameter taking values in the center of the gauge group. This allows us to use conformal field theory techniques to evaluate exactly various correlation functions at the critical point. In particular, we show that the plaquette operator of the gauge theory is mapped into the energy operator of the dimensionally reduced model. The plaquette expectation value in presence of static sources for three-dimensional SU(2) and SU(3) theories at the deconfinement temperature can be exactly evaluated, providing some new insight about the structure of the color flux tube in mesons and baryons.
We show that universality arguments, namely the Svetitsky-Yaffe conjecture, allow one to obtain exact results on the critical behavior of 3D SU(2) gauge theory at the finite temperature deconfinement transition,through a mapping into the 2D Ising model. In particular, we consider the finite-size scaling behavior of the plaquette operator, which can be mapped into the energy operator of the 2D Ising model. We obtain exact predictions for the dependence of the plaquette expectation value on the size and shape of the lattice and we compare them to Monte Carlo results, finding complete agreement. We discuss the application of this method to the computation of more general correlators of the plaquette operator at criticality, and its relevance to the study of the color flux tube structure.
Pomeron non factorization for the diffractive scattering is considered and an analysis of experimental data is performed with different cuts in the momentum fraction $ξ$. The results of the analysis are compared with the breaking predicted in the Genovese-Nikolaev-Zakharov model.
The quark-antiquark contribution to the BFKL kernel is calculated. Using the effective vertex for the $q\bar q$ pair production in the Reggeon-Reggeon collision we find this contribution by integrating the square of this vertex over relative transverse momenta and fractions of longitudinal momenta of produced particles.
The large rapidity gap events from HERA are analyzed within a model containing a pomeron and an $f$-reggeon contribution. The choice for the pomeron contribution is based on the Donnachie-Landshoff model. The dependence of the "effective intercept" of the pomeron on the momentum fraction $β$ and on its Bjorken variable $ξ$ is calculated.
There are two physically different interpretations of ``triviality'' in $(λΦ^4)_4$ theories. The conventional description predicts a second-order phase transition and that the Higgs mass $m_h$ must vanish in the continuum limit if $v$, the physical v.e.v, is held fixed. An alternative interpretation, based on the effective potential obtained in ``triviality-compatible'' approximations (in which the shifted `Higgs' field $h(x)\equiv Φ(x)-<Φ>$ is governed by an effective quadratic Hamiltonian) predicts a phase transition that is very weakly first-order and that $m_h$ and $v$ are both finite, cutoff-independent quantities. To test these two alternatives, we have numerically computed the effective potential on the lattice. Three different methods were used to determine the critical bare mass for the chosen bare coupling value. All give excellent agreement with the literature value. Two different methods for obtaining the effective potential were used, as a control on the results. Our lattice data are fitted very well by the predictions of the unconventional picture, but poorly by the conventional picture.
We test numerically the effective string description of the infrared limit of lattice gauge theories in the confining regime. We consider the 3d Z(2) lattice gauge theory, and we define ratios of Wilson loops such that the predictions of the effective string theory do not contain any adjustable parameters. In this way we are able to obtain a degree of accuracy high enough to show unambiguously that the flux--tube fluctuations are described, in the infrared limit, by an effective bosonic string theory.
In spite of the fact that the Gribov's theorem about the region of applicability of the soft emission factorization cannot be referred literally to the case of massless charged particles, it can be used for the calculation of soft emission amplitudes in such a case also. We demonstrate this for the gluon production amplitude in the multi-Regge kinematics with small transverse momentum.
Evaluating two-loop integrals in the transverse momentum space we obtain the trajectory of the Reggeized gluon in QCD in an explicit form in the two-loop approximation. It is presented as an expansion in powers of $(D-4)$ for the space-time dimension $D$ tending to the physical value $D=4$. As the result of a remarkable cancellation the third order pole in$D-4$ disappears in the trajectory and the expansion starts with $(D-4)^{-2}$.
We present a detailed discussion of Spontaneous Symmetry Breaking (SSB) in $(λΦ^4)_4$. In the usual approach, inspired by perturbation theory, one predicts a second-order phase transition, the Higgs mass $m_h$, related to the value of the renormalized 4-point coupling, gets smaller when increasing the ultraviolet cutoff and this leads to the generally quoted upper bounds $m_h<$700-900 GeV. On the other hand, by exploring the structure of the effective potential in those approximation consistent with `triviality', where the Higgs mass does not represent a measure of any observable interaction, SSB does not require an ultraviolet cutoff, the phase transition is first-order, such that the massless `Coleman-Weinberg' regime lies in the broken phase, and one gets only $m_h<$3 TeV from vacuum stability. To separate out the two alternatives, we present a precise lattice computation of the slope of the effective potential in the region of bare parameters indicated by the Luscher~\&~Weisz and Brahm's analysis of the critical line. Our lattice data strongly support the latter description of SSB. Indeed, our data cannot be reproduced in perturbation theory, and then they confirm the existence on the lattice of a remarkable phase of $(λΦ^4)_4$ where SSB is generated through ``dimensional transmutation'', and show no evidence for residual self-interaction effects of the shifted ``Higgs'' field $h(x)=Φ(x)-\langleΦ\rangle$, in agreement with ``triviality''.
Recent experimental data on diffractive deep inelastic scattering collected by the H1 and ZEUS Collaborations at HERA are analysed in a model with a non-linear trajectory in the pomeron flux. The $t$ dependence of the diffractive structure function $F_2^{D(4)}$ is predicted. The normalization of the pomeron flux and the (weak) $Q^2$ dependence of the pomeron structure function are revised as well.
$s$-channel discontinuity of quark-quark scattering amplitude with gluon quantum numbers in the $t$ channel and negative signature is calculated in the Regge kinematical region in the two-loop approximation. Using this discontinuity and assuming that the Regge asymptotic behaviour is given by the Reggeized gluon contribution, we calculate the gluon trajectory in the two-loop approximation. Remarkable cancellations lead to the independence of the trajectory on properties of the scattered quarks, confirming the gluon Reggeization.
Diffractive deep inelastic events with a large rapidity gap are analyzed by using a Regge model for the pomeron flux and a gluonic content for the pomeron. Contrary to the expectations, the simplest assumption for the pomeron trajectory gives the best agreement with the data on the ratio of diffractive to the total number of events. In this case the main properties of the model are described by an analytic expression.