arXiv subjects

Agustin Sabio Vera

Publications and source records attributed to Agustin Sabio Vera.

At least 37 records · Page 2Linked to original sources

arXiv2012

Graviton emission in Einstein-Hilbert gravity

The five-point amplitude for the scattering of two distinct scalars with the emission of one graviton in the final state is calculated in exact kinematics for Einstein-Hilbert gravity. The result, which satisfies the Steinmann relations, is expressed in Sudakov variables, finding that it corresponds to the sum of two gauge invariant contributions written in terms of a new two scalar - two graviton effective vertex. A similar calculation is carried out in Quantum Chromodynamics (QCD) for the scattering of two distinct quarks with one extra gluon in the final state. The effective vertices which appear in both cases are then evaluated in the multi-Regge limit reproducing the well-known result obtained by Lipatov where the Einstein-Hilbert graviton emission vertex can be written as the product of two QCD gluon emission vertices, up to corrections to preserve the Steinmann relations.

hep-th↗

arXiv2012

NLO jet vertex from Lipatov's QCD effective action

Real and virtual contributions to the quark-initiated forward jet vertex in QCD are calculated at next-to-leading logarithmic accuracy using Lipatov's effective action, valid in the high energy multi-Regge limit. A regularization of longitudinal divergencies is proposed which allows for the determination of jet observables. Agreement with previous results in the literature is found.

hep-ph↗

arXiv2010

Dual conformal invariance in the Regge limit

A dual conformal symmetry, analogous to the dual conformal symmetry observed for the scattering amplitudes of N=4 Super Yang-Mills theory, is identified in the Regge limit of QCD. Combined with the original two-dimensional conformal symmetry of the theory, this dual symmetry can potentially explain the integrability of the BFKL Hamiltonian. We also give evidence that the symmetry survives when a subset of unitarity corrections are taken into account by studying briefly the non-planar 2 to m reggeon transition vertices.

hep-th↗

arXiv2009

Structure Functions and Low-x -- Working Group Summary

A summary of recent results reported in the Structure Functions and Low-x working group at the DIS 2009 Workshop is given. Recent measurements of deep inelastic scattering cross sections and structure functions at HERA and of proton anti-proton collisions at Tevatron are presented. New developments of the extraction of parton distribution functions and of new theoretical developments are discussed.

hep-ex↗

arXiv2008

Resummations in QCD hard-scattering at large and small x

We discuss different resummations of large logarithms that arise in hard-scattering cross sections of quarks and gluons in regions of large and small x. The large-x logarithms are typically dominant near threshold for the production of a specified final state. These soft and collinear gluon corrections produce large enhancements of the cross section for many processes, notably top quark and Higgs production, and typically the higher-order corrections reduce the factorization and renormalization scale dependence of the cross section. The small-x logarithms are dominant in the regime where the momentum transfer of the hard sub-process is much smaller than the total collision energy. These logarithms are important to describe multijet final states in deep inelastic scattering and hadron colliders, and in the study of parton distribution functions. The resummations at small and large x are linked by the eikonal approximation and are dominated by soft gluon anomalous dimensions. We will review their role in both contexts and provide some explicit calculations at one and two loops.

hep-ph↗

arXiv2008

Critical formation of trapped surfaces in the collision of gravitational shock waves

We study the formation of marginally trapped surfaces in the head-on collision of two shock waves both in anti-de Sitter and Minkowski space-time in various dimensions as a function of the spread of the energy density in transverse space. For D=4 and D=5 it is shown that there exists a critical value of this spread above which no solution to the trapped surface equation is found. In four dimensions the trapped surface at criticality has a finite size, whereas in five the critical size vanishes. In both cases we find scaling relations characterized by critical exponents. Finally, when D>5 there is always a solution to the trapped surface equation for any transverse spread.

hep-th↗

arXiv2008

What HERA may provide ?

More than 100 people participated in a discussion session at the DIS08 workshop on the topic What HERA may provide. A summary of the discussion with a structured outlook and list of desirable measurements and theory calculations is given.

hep-ph↗

arXiv2008

Collinear improvement of the BFKL kernel in the electroproduction of two light vector mesons

We test the performance of a RG-improved kernel in the determination of the amplitude of a physical process, the electroproduction of two light vector mesons,in the BFKL approach at the next-to-leading approximation (NLA). We find that a smooth behavior of the amplitude with the center-of-mass energy can be achieved, setting the renormalization and energy scales appearing in the subleading terms to values much closer to the kinematical scales of the process than in approaches based on unimproved kernels.

hep-ph↗

arXiv2008

Critical gravitational collapse: towards a holographic understanding of the Regge region

We study the possible holographic connection between the Regge limit in QCD and critical gravitational collapse of a perfect fluid in higher dimensions. We begin by analyzing the problem of critical gravitational collapse of a perfect fluid in any number of dimensions and numerically compute the associated Choptuik exponent in d=5, 6 and 7 for a range of values of the speed of sound of the fluid. Using continuous self-similarity as guiding principle, a holographic correspondence between this process and the phenomenon of parton saturation in high-energy scattering in QCD is proposed. This holographic connection relates strong gravitational physics in the bulk with (nonsupersymmetric) QCD at weak coupling in four dimensions.

hep-th↗

arXiv2008

The High Energy Limit of QCD: BFKL Cross Sections

In this contribution we describe in some detail different aspects of the construction of BFKL cross sections. We focus on several effects which are relevant at next-to-leading order. In particular, we describe QCD coherence in DIS final states, improvements of the collinear region in multi-Regge kinematics, inclusive jet production at next-to-leading order, and azimuthal angle decorrelations of Mueller-Navelet jets at hadron colliders.

hep-ph↗

arXiv2008

Collinear improvement of the BFKL kernel in the electroproduction of two light vector mesons

The use of the BFKL kernel improved by the inclusion of subleading terms generated by renormalization group (RG) analysis has been suggested to cure the instabilities in the behavior of the BFKL Green's function in the next-to-leading approximation (NLA). We test the performance of a RG-improved kernel in the determination of the amplitude of a physical process, the electroproduction of two light vector mesons, in the BFKL approach in the NLA. We find that a smooth behavior of the amplitude with the center-of-mass energy can be achieved, setting the renormalization and energy scales appearing in the subleading terms to values much closer to the kinematical scales of the process than in the approaches based on the unimproved kernel.

hep-ph↗

arXiv2007

Angular decorrelations in Mueller-Navelet jets and DIS

We discuss the azimuthal angle decorrelation of Mueller-Navelet jets at hadron colliders and forward jets in Deep Inelastic Scattering within the BFKL framework with a NLO kernel. We stress the need of collinear improvements to obtain good perturbative convergence. We provide estimates of these decorrelations for large rapidity differences at the Tevatron, LHC and HERA.

hep-ph↗

arXiv2007

Azimuthal decorrelation of forward jets in Deep Inelastic Scattering

We study the azimuthal angle decorrelation of forward jets in Deep Inelastic Scattering. We make predictions for this observable at HERA describing the high energy limit of the relevant scattering amplitudes with quasi-multi-Regge kinematics together with a collinearly improved evolution kernel for multiparton emissions.

hep-ph↗

arXiv2007

BFKL Effects in Azimuthal Angle Correlations of Forward Jets

The azimuthal angle correlation of Mueller-Navelet jets at hadron colliders is studied in the NLO BFKL formalism. We highlight the need of collinear improvements in the kernel to obtain good convergence properties and we obtain better fits for the Tevatron data than at LO accuracy. We also estimate these correlations for larger rapidity differences available at the LHC.

hep-ph↗

arXiv2007

The azimuthal decorrelation of jets widely separated in rapidity as a test of the BFKL kernel

We study the decorrelation in azimuthal angle of Mueller-Navelet jets at hadron colliders within the BFKL formalism. We introduce NLO terms in the evolution kernel and present a collinearly-improved version of it for all conformal spins. We show how this further resummation has good convergence properties and is closer to the Tevatron data than a simple LO treatment. However, we are still far from a good fit. We offer estimates of these decorrelations for larger rapidity differences which should favor the onset of BFKL effects and encourage experimental studies of this observable at the LHC.

hep-ph↗

arXiv2006

W-boson production with large transverse momentum at the LHC

We study W-boson production with large transverse momentum, Q_T, in pp collisions at the LHC. We calculate the complete NLO corrections and the soft-gluon NNLO corrections to the differential cross section. The NLO corrections are large but they do not reduce the scale dependence relative to LO, while the NNLO soft-gluon corrections, although small, significantly reduce the scale dependence and thus provide a more stable result.

hep-ph↗

arXiv2006

The effect of NLO conformal spins in azimuthal angle decorrelation of jet pairs

Azimuthal angle decorrelation in inclusive dijet cross sections is studied analytically to take into account the next-to-leading corrections to the BFKL kernel while keeping the jet vertices at leading order. The spectral representation on the basis of leading order eigenfunctions is generalized to include the dependence on conformal spins. With this procedure running coupling effects and angular dependences are both included. It is shown how the angular decorrelation for jets with a wide relative separation in rapidity largely decreases at this higher order in the resummation.

hep-ph↗

arXiv2005

Different Aspects of BFKL at NLL

Progress in the understanding of the BFKL approach in the NLL approximation is reported. The study based on the iteration of the kernel using the exponentiation of the gluon Regge trajectory is reviewed in QCD and N=4 super Yang-Mills theories. Properties of the gluon Green's function in the high energy Regge limit for forward and non-forward scattering are considered. A novel representation of collinearly improved kernels is also presented.

hep-ph↗