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J. Wagner

Publications and source records attributed to J. Wagner.

84 records · Page 5Linked to original sources
arXiv2011

On timelike Compton scattering at medium and high energies

We emphasize the complementarity of timelike and spacelike studies of deep exclusive processes, taking as an example the case of timelike Compton Scattering (TCS) i.e. the exclusive photoproduction of a lepton pair with large invariant mass, vs deeply virtual Compton scattering (DVCS) i.e. the exclusive leptoproduction of a real photon. Both amplitudes factorize with the same generalized parton distributions (GPDs) as their soft parts and coefficient functions which differ significantly at next to leading order in alpha_s. We also stress that data on TCS at very high energy should be available soon thanks to the study of ultraperipheral collisions at the LHC, opening a window on quark and gluon GPDs at very small skewness.

hep-ph↗
arXiv2011

NLO corrections to timelike, spacelike and double deeply virtual Compton scattering

We calculate the O(alpha_s) corrections to the timelike, spacelike and double deeply virtual Compton scattering amplitudes in the generalized Bjorken scaling region. Special attention is devoted to studies of the difference between the next to leading order timelike and spacelike coefficient functions, which plays for this process a role analogous to the large K factor which was much discussed in the analysis of inclusive Drell Yan cross sections. Also in the present studies the timelike nature of the hard scale gives rise to new absorptive part of the amplitude and to the presence of characteristic pi^2 terms, which can potentially lead to sizeable corrections.

hep-ph↗
arXiv2009

Timelike Compton Scattering in Ultraperipheral Collisions

Exclusive photoproduction of dileptons, gamma N ->l+l- N, is and will be measured in ultraperipheral collisions at hadron colliders. We demonstrate that the timelike deeply virtual Compton scattering (TCS) mechanism gamma q -> l+l- q, where the lepton pair comes from the subprocess gamma q -> gamma* q, dominates in some accessible kinematical regions, thus opening a new way to study generalized parton distributions (GPD) in the nucleon at small skewedness.

hep-ph↗
arXiv2009

Timelike Compton Scattering at LHC

Exclusive photoproduction of dileptons, gamma N ->l+l- N, is and will be measured in ultraperipheralcollisions at hadron colliders. We demonstrate that the timelike deeply virtual Compton scattering (TCS) mechanism gamma q -> l+l- q, where the lepton pair comes from the subprocess gamma q -> gamma* q, dominates in some accessible kinematical regions, thus opening a new way to study generalized parton distributions (GPD) in the nucleon at small skewedness.

hep-ph↗
arXiv2008

Can one measure timelike Compton scattering at LHC ?

Exclusive photoproduction of dileptons, gamma N->e+e-N, is and will be measured in ultraperipheral collisions at hadron colliders, such as the Tevatron, RHIC and the LHC . We demonstrate that the timelike deeply virtual Compton scattering (TCS) mechanism gamma q -> e+e- q where the lepton pair comes from the subprocess gamma q -> gamma* q dominates in some accessible kinematical regions, thus opening a new way to study generalized parton distributions (GPD) in the nucleon. High energy kinematics enables to probe parton distributions at small skewedness. This subprocess interferes at the amplitude level with the pure QED subprocess gamma gamma* -> e+e- where the virtual photon is radiated from the nucleon.

hep-ph↗
arXiv2008

How Does Quantum Vacuum Energy Accelerate?

We show that Casimir energy for a configuration of parallel plates gravitates according to the equivalence principle both for the finite and divergent parts. This shows that the latter can be absorbed by a process of renormalization.

hep-th↗
arXiv2008

Exclusive photoproduction of lepton pairs at LHC

Exclusive photoproduction of dileptons, gamma p ->l+ l- p, will be measured in ultraperipheral collisions at LHC. The mechanism where the lepton pair comes from a heavy timelike photon radiated from a quark interferes with the pure QED process gamma gamma ->l+ l- As an analog of deeply virtual Compton scattering, this timelike Compton scattering is a way to study generalized parton distributions in the nucleon or the nucleus. High energy kinematics will enable to focus on gluon distributions. Nuclear effects may be scrutinized in heavy ion collisions.

hep-ph↗
arXiv2006

(Non)decoupling of the Higgs triplet effects

We consider the electroweak theory with an additional Higgs triplet at one loop using the hybrid renormalization scheme based on $α_{\rm EM}$, $G_F$ and $M_Z$ as input observables. We show that in this scheme loop corrections can be naturally split into the Standard Model part and corrections due to ``new physics''. The latter, however do not decouple in the limit of infinite triplet mass parameter, if the triplet trilinear coupling to SM Higgs doublets grows along with the the triplet mass. In electroweak observables computed at one loop this effect can be attributed to radiative generation in this limit of a nonvanishing vacuum expectation value of the triplet. We also point out that whenever tree level expressions for the electroweak observables depend on vacuum expectation values of scalar fields other than the Standard Model Higgs doublet, tadpole contribution to the ``oblique'' parameter $T$ should in principle be included. In the Appendix the origin of nondecoupling is discussed on the basis of symmetry principles in a simple scalar field theory.

hep-ph↗
arXiv2006

Surface Divergences and Boundary Energies in the Casimir Effect

Although Casimir, or quantum vacuum, forces between distinct bodies, or self-stresses of individual bodies, have been calculated by a variety of different methods since 1948, they have always been plagued by divergences. Some of these divergences are associated with the volume, and so may be more or less unambiguously removed, while other divergences are associated with the surface. The interpretation of these has been quite controversial. Particularly mysterious is the contradiction between finite total self-energies and surface divergences in the local energy density. In this paper we clarify the role of surface divergences.

hep-th↗
arXiv2006

Z' and the Appelquist-Carrazzone decoupling

We consider the electroweak theory with an additional neutral vector boson $Z^\prime$ at one loop. We propose a renormalization scheme which makes the decoupling of heavy $Z^\prime$ effects manifest. The proposed scheme justifies the usual procedure of performing fits to the electroweak data by combining the full SM loop corrections to observables with the tree level corrections due to the extended gauge structure. Using this scheme we discuss in the model with extra an $U(1)^\prime$ group factor 1-loop results for the $ρ$ parameters defined in several different ways.

hep-ph↗
arXiv2004

Translation Symmetry Breaking in the One-Component Plasma on the Cylinder

The two-dimensional one-component plasma, i.e. the system of point-like charged particles embedded in a homogeneous neutralizing background, is studied on the surface of a cylinder of finite circumference, or equivalently in a semiperiodic strip of finite width. The model has been solved exactly by Choquard et al. at the free-fermion coupling $Γ=2$: in the thermodynamic limit of an infinitely long strip, the particle density turns out to be a nonconstant periodic function in space and the system exhibits long-range order of the Wigner-crystal type. The aim of this paper is to describe, qualitatively as well as quantitatively, the crystalline state for a larger set of couplings $Γ=2γ$ ($γ=1,2,...$ a positive integer) when the plasma is mappable onto a one-dimensional fermionic theory. The fermionic formalism, supplemented by some periodicity assumptions, reveals that the density profile results from a hierarchy of Gaussians with a uniform variance but with different amplitudes. The number and spatial positions of these Gaussians within an elementary cell depend on the particular value of $γ$. Analytic results are supported by the exact solution at $γ=1$ ($Γ=2$) and by exact finite-size calculations at $γ=2,3$.

cond-mat.stat-mech↗