2,039 research outputs found
Deeply Virtual Neutrino Scattering at Leading Twist
We illustrate the generalization of results concerning exclusive
electromagnetic processes in the deeply virtual limit (DVCS) to the case of the
weak interactions.We briefly describe the derivation of the differential cross
section for neutrino-nucleon reactions mediated by the neutral current and the
amplitude for similar reactions mediated by the charged currents.Comment: 3 pages, 3 figures, Talk Presented at Neutrino Oscillations Workshop
(NOW 2006), Otranto, Lecce, Italy, September 9-16 200
production at hadron colliders
We study the production of a single top quark in association with a heavy
extra at hadron colliders in new physics models with and without
flavor-changing neutral-current (FCNC) couplings. We use QCD soft-gluon
resummation and threshold expansions to calculate higher-order corrections for
the total cross section and transverse-momentum distributions for
production. The impact of the uncertainties due to the structure of the proton
and scale dependence is also analyzed.Comment: 35 pages, 23 figures, regular article; published version of the
manuscript appearing in Eur. Phys. J. C 80, 467 (2020
Extra s and s in Heterotic--String Derived Models
The ATLAS collaboration recently recorded possible excess in the di--boson
production at the di--boson invariant mass at around 2 TeV. Such an excess may
be produced if there exist additional and/or at that
scale. We survey the extra s and s that may arise from
semi--realistic heterotic string vacua in the free fermionic formulation in
seven distinct cases including: ; family universal
not in ; non--universal ; hidden
sector symmetries and kinetic mixing; left--right symmetric models;
Pati--Salam models; leptophobic and custodial symmetries. Each case has a
distinct signature associated with the extra symmetry breaking scale. In one of
the cases we explore the discovery potential at the LHC using resonant
leptoproduction. Existence of extra vector boson with the reported properties
will significantly constrain the space of allowed string vacua.Comment: 25 pages, 2 figures. Standard LaTeX. References added. Published
versio
Using and Constraining Nonforward Parton Distributions (Deeply Virtual Neutrino Scattering in Cosmic Rays and Light Dark Matter Searches)
We overview the construction of Nonforward Parton Distributions (NPD) in
Deeply Virtual Compton Scattering (DVCS). Then we turn to the analysis of
similar constructs in the weak sector (electroweak NPD's). We argue in favour
of a possible use of electroweak DVCS (EWDVCS) as a rare process for the study
of neutrinos in cosmic rays and for light dark matter detection in underground
experimentsComment: 10 pages 7 figures. Based on a talk presented by C. Coriano` at
QCD@work 2003, Conversano, Italy June 200
Gauged Axions and their QCD Interactions
We present a brief overview of axion models associated to anomalous abelian
(gauge) symmetries, discussing their main phenomenological features. Among
these, the mechanism of vacuum misalignment introduced at the QCD and at the
electroweak phase transitions, with the appearance of periodic potentials,
responsible for the generation of a mass for these types of axions.Comment: 8 pages, 6 figures. Presented at QCD@Work - International Workshop on
QCD - Theory and Experiment 20-23 June 2010 Martina Franca - Valle d'Itria -
Italy, to appear in the AIP Conference Proceedings Series 201
Parton Distributions, Logarithmic Expansions and Kinetic Evolution
Aspects of the QCD parton densities are briefly reviewed, drawing some
parallels to the density matrix formulation of quantum mechanics, exemplified
by Wigner functions. We elaborate on the solution of their evolution equations
using logarithmic expansions and overview their kinetic interpretation. We
illustrate how a Fokker-Planck equation can be derived using the master
formulation of the same equations and its construction in the case of the
transverse spin distributions. A simple connection of the leading order DGLAP
equation to fractional diffusion using fractional calculus is also briefly
outlined.Comment: Review article to appear in Lecture Notes of SIM (S. Dragomir ed.) 32
pages, 1 figur
DIS2015 Heavy Flavours Working Group Summary
Studies presented in the heavy flavours working group are summarized. Very
recent results of measurements at the HERA, LHC, Tevatron, STAR, PHENIX, and
BaBar experiments are reviewed and new developments in theory and phenomenology
are discussed. In particular, aspects of the impact of heavy flavours on global
QCD analyses to determine the structure of the proton, and analyses in physics
beyond the Standard Model are considered.Comment: 16 pages, 16 figures, Conference proceeding summary, DIS2015 "The
XXIII International Workshop on Deep Inelastic Scattering and Related
Subjects", April 27 - May 1, 2015, Southern Methodist University, Dallas,
Texas, US
Relic Densities of Dark Matter in the U(1)-Extended NMSSM and the Gauged Axion Supermultiplet
We compute the dark matter relic densities of neutralinos and axions in a
supersymmetric model with a gauged anomalous U(1) symmetry, kinetically mixed
with of hypercharge. The model is a variant of the USSM (the U(1)
extended NMSSM), containing an extra U(1) symmetry and an extra singlet in the
superpotential respect to the MSSM, where gauge invariance is restored by
Peccei-Quinn interactions using a Stuckelberg multiplet. This approach
introduces an axion (Im b) and a saxion (Re b) in the spectrum and generates an
axino component for the neutralino. The Stuckelberg axion (Im b) develops a
physical component (the gauged axion) after electroweak symmetry breaking. We
classify all the interactions of the Lagrangian and perform a complete
simulation study of the spectrum, determining the neutralino relic densities
using micrOMEGAs. We discuss the phenomenological implications of the model
analyzing mass values for the axion from the milli-eV to the MeV region. The
possible scenarios that we analyze are significantly constrained by a
combination of WMAP data, the exclusion limits from direct axion searches and
the veto on late entropy release at the time of nucleosynthesis.Comment: 43 pages, 11 figures. Revised final version, accepted for publication
in Phys. Rev.
Differential cross sections for top pair production at the LHC
We present results of phenomenological studies for top-quark pair production
at the LHC at the center of mass energy TeV. The transverse
momentum and rapidity distributions for final-state top quarks are calculated
in perturbative QCD at approximate next-to-next-to-leading order by using methods of threshold resummation beyond the leading
logarithmic accuracy. The theoretical predictions are obtained by using the
computer code \textsc{DiffTop} and are compared to recent measurements by the
ATLAS and CMS collaborations. \textsc{Difftop} can be employed in the general
case of heavy-quark pair production at hadron-hadron colliders and provides a
basis for applications in QCD analyses for parton distribution functions
determination.Comment: 6 pages, 2 figures, Conference proceedings for DIS2014, XXII
International Workshop on Deep-Inelastic Scattering and Related Subjects, 28
April - 2 May 2014, Warsaw, Poland, and ICHEP 2014, 37 International
Conference on High Energy Physics, 2-9 July 2014, Valencia, Spai
Nonperturbative contributions to a resummed leptonic angular distribution in inclusive neutral vector boson production
We present an analysis of nonperturbative contributions to the transverse
momentum distribution of bosons produced at hadron colliders. The
new data on the angular distribution of Drell-Yan pairs measured
at the Tevatron is shown to be in excellent agreement with a perturbative QCD
prediction based on the Collins-Soper-Sterman (CSS) resummation formalism at
NNLL accuracy. Using these data, we determine the nonperturbative component of
the CSS resummed cross section and estimate its dependence on arbitrary
resummation scales and other factors. With the scale dependence included at the
NNLL level, a significant nonperturbative component is needed to describe the
angular data.Comment: 36 pages, 10 figures, regular article. Revised version accepted for a
publication in Phys.Rev.
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