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R. Peschanski

Publications and source records attributed to R. Peschanski.

At least 19 recordsLinked to original sources
arXiv2026

Determination of the Odderon amplitude in elastic cross-sections at high energies from scaling and analyticity

Scaling amplitudes describing $pp$ elastic scattering differential cross-sections in the dip-bump region of momentum transfer at the LHC have been recently derived~\cite{scaling}. We check that the same scaling is verified by the $p\bar p$ cross-section at the highest energy of the Tevatron. Applying the general "energy to phase" relation for a given signature, coming from the analiticity properties inherent to the S-Matrix formalism~\cite{chew}, we derive the scaling amplitude with positive signature (i.e. the Pomeron). Fitting the $pp$ differential cross-sections measured by the TOTEM collaboration leads to some tension with data in the experimental dip observed at moderate momentum transfer. Concentrating the study to the dip/bump region, we are able to determine a contribution of a negative signature amplitude (i.e. the Odderon) leading to a parameter free prediction for the $p\bar p$ differential cross-section which is in agreement with the D0 data. The extraction of the Odderon amplitude in both modulus and phase is then performed and discussed.

hep-ph↗
arXiv2026

The scaling Pomeron

We examine the Regge theoretical properties for the scaling observed in pp elastic scattering differential cross-sections at the LHC. A positive signature amplitude (i.e. the Pomeron) with scaling properties has been derived. It is found to describe the dip-bump region of momentum transfer at LHC energies in agreement with data. We derive the analytic continuation in the whole plane of the t-channel partial waves of index $l_t$ specific to the Regge formalism. The analytic form of the amplitude exhibits a specific scaling property without singularities, except for a series of poles in the $l_t$ real axis at fractional values.

hep-ph↗
arXiv2025

Matrix approximations of operators

The approximate representation of operators by finite matrices is analysed in terms of accuracy and convergence. The identity operator, for example, can be reconstructed using a basis of harmonic oscillator states leading to a narrow peak approximation of the $\delta$ function, but this peak may be perturbed by small, residual, oscillations. The peak does not shrink nor grows quickly, and the oscillations only diminish slowly as the size of the matrix increases. For the kinetic energy operator, a triple peak (one positive, two negative) representation of $-\delta''$ is obtained, but that is affected also by residual oscillations. Again, convergence is slow as the matrix dimension increases. We find compact formulas to explain such oscillations. Similar observations are found for representations of local interactions, while separable potentials are better represented. As a comparison, in the context of a toy model, the effects of choosing an alternative single particle basis are studied. A formal approach for the approximation of operators is considered for comparison. We conclude with a word of caution for (finite) matrix approximations of operators.

math-ph↗
arXiv2024

A QCD interpretation of the scaling observed in the LHC proton-proton elastic cross-sections at moderate transfer momentum

A phenomenological scaling property of the LHC proton-proton elastic scattering cross sections at moderate transfer momentum has been recently observed. The theoretical QCD saturation framework for hard elastic scattering on the proton, which we recall, predicts a strikingly similar scaling property in the same configuration of energy and momentum transfer. This similarity favors a theoretical interpretation where the hard amplitude is the building block of the $pp$ amplitude via unitarization. The values of the scaling exponents favor two QCD saturation approaches where the saturation scale exponent is of order one half of that which is found for hard elastic scattering and deep inelastic processes on the proton.

hep-ph↗
arXiv2018

Profile of a Galactic Spherical Cloud of Self-Gravitating Fermions

The field which binds a thermal fermionic cloud is defined as a Hartree integral upon its density. In turn, the density results from the field via a Thomas-Fermi occupation of the local phase space. This defines a complete theory of all properties and observables for the cloud. As an application to dark matter halos, comparisons with astronomic data on dwarf spheroidal galaxies are provided and discussed. Estimates of the elementary fermion mass are obtained, serving as a phase-space bound on fermionic dark matter.

hep-th↗
arXiv2011

Reggeon exchange from gauge/gravity duality

We perform the analysis of quark-antiquark Reggeon exchange in meson-meson scattering, in the framework of the gauge/gravity correspondence in a confining background. On the gauge theory side, Reggeon exchange is described as quark-antiquark exchange in the t channel between fast projectiles. The corresponding amplitude is represented in terms of Wilson loops running along the trajectories of the constituent quarks and antiquarks. The paths of the exchanged fermions are integrated over, while the "spectator" fermions are dealt with in an eikonal approximation. On the gravity side, we follow a previously proposed approach, and we evaluate the Wilson-loop expectation value by making use of gauge/gravity duality for a generic confining gauge theory. The amplitude is obtained in a saddle-point approximation through the determination near the confining horizon of a Euclidean "minimal surface with floating boundaries", i.e., by fixing the trajectories of the exchanged quark and antiquark by means of a minimisation procedure, which involves both area and length terms. After discussing, as a warm-up exercise, a simpler problem on a plane involving a soap film with floating boundaries, we solve the variational problem relevant to Reggeon exchange, in which the basic geometry is that of a helicoid. A compact expression for the Reggeon-exchange amplitude, including the effects of a small fermion mass, is then obtained through analytic continuation from Euclidean to Minkowski space-time. We find in particular a linear Regge trajectory, corresponding to a Regge-pole singularity supplemented by a logarithmic cut induced by the non-zero quark mass. The analytic continuation leads also to companion contributions, corresponding to the convolution of the same Reggeon-exchange amplitude with multiple elastic rescattering interactions between the colliding mesons.

hep-th↗
arXiv2009

Hydrodynamic Flow of the Quark-Gluon Plasma and Gauge/Gravity Correspondence

The contribution presents a summary of the Gauge/Gravity approach to the study of hydrodynamic flow of the quark-gluon plasma formed in heavy-ion collisions. Considering the ideal case of a supersymmetric Yang-Mills theory for which the AdS/CFT correspondence gives a precise form of the Gauge/Gravity duality, the properties of the strongly coupled expanding plasma are put in one-to-one correspondence with the metric of a 5-dimensional black hole moving away in the 5th dimension and its deformations consistent with the relevant Einstein equations. Several recently studied aspects of this framework are recalled and put in perspective. This paper is a written version of the four lectures given by the authors on that subject.

hep-th↗
arXiv2008

Hybrid Pomeron Model of exclusive central diffractive production

Central diffractive production of heavy states (massive dijets, Higgs boson) is studied in the exclusive mode using a new Hybrid Pomeron Model (HPM). Built from Hybrid Pomerons defined by the combination of one hard and one soft color exchanges, the model describes well the centrally produced diffractive dijet data at the Tevatron. Predictions for the Higgs boson and dijet exclusive production at the LHC are presented.

hep-ph↗
arXiv2008

Limiting fragmentation from scale-invariant merging of fast partons

Exploiting the idea that the fast partons of an energetic projectile can be treated as sources of color radiation interpreted as wee partons, it is shown that the recently observed property of extended limiting fragmentation implies a scaling law for the rapidity distribution of fast partons. This leads to a picture of a self-similar process where, for fixed total rapidity Y, the sources merge with probability varying as 1/y.

hep-ph↗
arXiv2008

Next-to-leading BFKL phenomenology of forward-jet cross sections at HERA

We show that the forward-jet measurements performed at HERA allow for a detailed study of corrections due to next-to-leading logarithms (NLL) in the Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach. While the description of the dσ/dx data shows small sensitivity to NLL-BFKL corrections, these can be tested by the triple differential cross section dσ/dxdk_T^2dQ^2 recently measured. These data can be successfully described using a renormalization-group improved NLL kernel while the standard next-to-leading-order QCD or leading-logarithm BFKL approaches fail to describe the same data in the whole kinematic range. We present a detailed analysis of the NLL scheme and renormalization-scale dependences and also discuss the photon impact factors.

hep-ph↗
arXiv2007

Next-leading BFKL effects in forward-jet production at HERA

We show that next-leading logarithmic (NLL) Balitsky-Fadin-Kuraev-Lipatov (BFKL) effects can be tested by the forward-jet cross sections recently measured at HERA. For dσ/dx, the NLL corrections are small which confirms the stability of the BFKL description. The triple differential cross section dσ/dxdk_T^2dQ^2 is sensitive to NLL effects and opens the way for an experimental test of the full BFKL theoretical framework at NLL accuracy.

hep-ph↗
arXiv2007

Exclusive vector meson production at HERA from QCD with saturation

Following recent predictions that the geometric scaling properties of deep inelastic scattering data in inclusive gamma*-p collisions are expected also in exclusive diffractive processes, we investigate the diffractive production of vector mesons. Using analytic results in the framework of the BK equation at non-zero momentum transfer, we extend to the non-forward amplitude a QCD-inspired forward saturation model including charm, following the theoretical predictions for the momentum transfer dependence of the saturation scale. We obtain a good fit to the available HERA data and make predictions for deeply virtual Compton scattering measurements.

hep-ph↗
arXiv2007

Universality of traveling waves with QCD running coupling

``Geometric scaling'', i.e. the dependence of DIS cross-sections on the ratio Q/Q_S, where Q_S(Y) is the rapidity-dependent \saturation scale, can be theoretically obtained from universal ``traveling wave'' solutions of the nonlinear Balitsky-Kovchegov (BK) QCD evolution equation at fixed coupling. We examine the similar mean-field predictions beyond leading-logarithmic order, including running QCD coupling.

hep-ph↗
arXiv2007

Unified description of Bjorken and Landau 1+1 hydrodynamics

We propose a generalization of the Bjorken in-out Ansatz for fluid trajectories which, when applied to the (1+1) hydrodynamic equations, generates a one-parameter family of analytic solutions interpolating between the boost-invariant Bjorken picture and the non boost-invariant one by Landau. This parameter characterises the proper-time scale when the fluid velocities approach the in-out Ansatz. We discuss the resulting rapidity distribution of entropy for various freeze-out conditions and compare it with the original Bjorken and Landau results.

nucl-th↗
arXiv2007

Diffractive $χ$ Production at the Tevatron and the LHC

We present predictions for the diffractive production of $χ$ mesons in the central rapidity region usually covered by collider detectors. The predicted cross sections are based on the Bialas-Landshoff formalism for both exclusive and inclusive production and makes use of the DPEMC Monte-Carlo simulation adapted with kinematics appropriate for small-mass diffractive production. We compare generator-level results with a CDF measurement for exclusive $χ$ production, and study background and other scenarios including the contribution of inclusive $χ$ production. The results agree with the Tevatron data and are extrapolated, highlighting the exclusive $\chic$ production at LHC energies. A possible new measurement at the Tevatron using the DØforward detectors is investigated, taking advantage of the dominance of exclusive production for high enough diffractive mass fraction.

hep-ph↗
arXiv2006

QCD traveling waves beyond leading logarithms

We derive the asymptotic traveling-wave solutions of the nonlinear 1-dimensional Balitsky-Kovchegov QCD equation for rapidity evolution in momentum-space, with 1-loop running coupling constant and equipped with the Balitsky-Kovchegov-Kuraev-Lipatov kernel at next-to-leading logarithmic accuracy, conveniently regularized by different resummation schemes. Traveling waves allow to define "universality classes" of asymptotic solutions, i.e. independent of initial conditions and of the nonlinear damping. A dependence on the resummation scheme remains, which is analyzed in terms of geometric scaling properties.

hep-ph↗