399 research outputs found
Hadron multiplicity induced by top quark decays at the LHC
The average charged hadron multiplicities induced by top quark decays are
calculated in pQCD at LHC energies. Different modes of top production are
considered. Proposed measurements can be used as an additional test of pQCD
calculations independent on a fragmentation model.Comment: 12 pages, 12 figures, to be published elsewher
Open charm and beauty production in hadron reactions
The production of charmed and beauty hadrons in proton-proton and
proton-antiproton collisions at high energies is analyzed within the modified
quark-gluon string model (QGSM) including the internal motion of quarks in
colliding hadrons. It is shown that using both the QGSM and NLO QCD one can
describe the experimental data rather successfully in a wide region of
transverse momenta. We also present some predictions for the future experiments
on the beauty baryon production in collisions at LHC energies and on the
charmed meson production in reactions at GSI energies.Comment: 8 pages, 10 figures. Talk given at International Conference on Hadron
Structure (HS 09), Tatranska Strba, Slovak Republic, August 29th-September
3rd, 200
Higher Grading Conformal Affine Toda Teory and (Generalized) Sine-Gordon/Massive Thirring Duality
Some properties of the higher grading integrable generalizations of the
conformal affine Toda systems are studied. The fields associated to the
non-zero grade generators are Dirac spinors. The effective action is written in
terms of the Wess-Zumino-Novikov-Witten (WZNW) action associated to an affine
Lie algebra, and an off-critical theory is obtained as the result of the
spontaneous breakdown of the conformal symmetry. Moreover, the off-critical
theory presents a remarkable equivalence between the Noether and topological
currents of the model. Related to the off-critical model we define a real and
local Lagrangian provided some reality conditions are imposed on the fields of
the model. This real action model is expected to describe the soliton sector of
the original model, and turns out to be the master action from which we uncover
the weak-strong phases described by (generalized) massive Thirring and
sine-Gordon type models, respectively. The case of any (untwisted) affine Lie
algebra furnished with the principal gradation is studied in some detail.
The example of is presented explicitly.Comment: 28 pages, JHEP styl
Is Vtb=1 ?
The strongest constraint on Vtb presently comes from the 3 x 3 unitarity of
the CKM matrix, which fixes Vtb to be very close to one. If the unitarity is
relaxed, current information from top production at Tevatron still leaves open
the possibility that Vtb is sizably smaller than one. In minimal extensions of
the standard model with extra heavy quarks, the unitarity constraints are much
weaker and the EW precision parameters entail the strongest bounds on Vtb. We
discuss the experimental perspectives of discovering and identifying such new
physics models at the Tevatron and the LHC, through a precise measurement of
Vtb from the single top cross sections and by the study of processes where the
extra heavy quarks are produced.Comment: 19 pages, 8 figure
Graviton-induced Bremsstrahlung
We discuss photon Bremsstrahlung induced by virtual graviton exchange in
proton-proton interactions at hadronic colliders, resulting from the exchange
of Kaluza-Klein excitations of the graviton. The relevant subprocesses, gg to G
to e^+e^-gamma and q barq to e^+e^-gamma are discussed in both the ADD and the
RS scenarios. Although two-body final states (or real graviton emission) would
presumably be the main discovery channels, a search for three-body final states
could be worthwhile since such events have characteristic features that could
provide additional confirmation. In particular, the k_perp-distribution of the
photon is in both scenarios harder than that of the Standard-model background.Comment: 24 pages, including figures. v2: Including initial-state
Bremsstrahlung and photon k_perp spectra. Version to appear in PR
Associated Production of Bottomonia and Higgs Bosons at Hadron Colliders
We study the associated production of bottomonia and Higgs bosons at hadron
colliders within the factorization formalism of nonrelativistic quantum
chromodynamics providing all contributing partonic cross sections in analytic
form. While such processes tend to be suppressed in the standard model, they
may have interesting cross sections in its minimal supersymmetric extension,
especially at large values of tan(beta), where the bottom Yukawa couplings are
enhanced. We present numerical results for the processes involving the lighter
CP-even h^0 boson and the CP-odd A^0 boson appropriate for the Fermilab
Tevatron and the CERN LHC.Comment: 33 pages, 7 figures, Latex, to appear in Phys. Rev.
On the mechanisms of heavy-quarkonium hadroproduction
We discuss the various mechanisms potentially at work in hadroproduction of
heavy quarkonia in the light of computations of higher-order QCD corrections
both in the Colour-Singlet (CS) and Colour-Octet (CO) channels and the
inclusion of the contribution arising from the s-channel cut in the CS channel.
We also discuss new observables meant to better discriminate between these
different mechanisms.Comment: Invited review talk at 3rd International Conference On Hard And
Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008), 8-14 June
2008, Illa da Toxa, Galicia, Spain. 11 pages, 21 figures, LaTeX, uses
svjour.cls and svepj.clo (included
Large Extra Dimensions and Decaying KK Recurrences
We suggest the possibility that in ADD type brane-world scenarios, the higher
KK excitations of the graviton may decay to lower ones owing to a breakdown of
the conservation of extra dimensional ``momenta'' and study its implications
for astrophysics and cosmology. We give an explicit realization of this idea
with a bulk scalar field , whose nonzero KK modes acquire vacuum
expectation values. This scenario helps to avoid constraints on large extra
dimensions that come from gamma ray flux bounds in the direction of nearby
supernovae as well as those coming from diffuse cosmological gamma ray
background. It also relaxes the very stringent limits on reheat temperature of
the universe in ADD models.Comment: 16 pages, late
Fatigue in Women with Fibromyalgia: A Gene-Physical Activity Interaction Study
Fatigue is a cardinal symptom in fibromyalgia. Fatigue is assumed to be the result of genetic susceptibility and environmental factors. We aimed at examining the role of genetic susceptibility for fatigue in southern Spanish women with fibromyalgia, by looking at single nucleotide polymorphisms in 34 fibromyalgia candidate-genes, at the interactions between genes, and at the gene-physical activity interactions. We extracted DNA from saliva of 276 fibromyalgia women to analyze gene-polymorphisms. Accelerometers registered physical activity and sedentary behavior. Fatigue was assessed with the Multidimensional Fatigue Inventory. Based on the Bonferroni's and False Discovery Rate values, we found that the genotype of the rs4453709 polymorphism (sodium channel protein type 9 subunit alpha, SCN9A, gene) was related to reduced motivation (AT carriers showed the highest reduced motivation) and reduced activity (AA carriers showed the lowest reduced activity). Carriers of the heterozygous genotype of the rs1801133 (methylene tetrahydrofolate reductase, MTHFR, gene) or rs4597545 (SCN9A gene) polymorphisms who were physically active reported lower scores on fatigue compared to their inactive counterparts. Highly sedentary carriers of the homozygous genotype of the rs7607967 polymorphism (AA/GG genotype; SCN9A gene) presented more reduced activity (a dimension of fatigue) than those with lower levels of sedentary behavior. Collectively, findings from the present study suggest that the contribution of genetics and gene-physical activity interaction to fatigue in fibromyalgia is modest
Strong coupling of excited heavy mesons
We compute the strong coupling constant , where () is the wave state, by QCD sum rules and by light-cone sum rules. The two methods give
compatible results in the limit , with a rather large value of
the coupling constant. We apply the results to the calculation of the hadronic
widths of the positive parity and states and to the chiral loop
contribution to the ratio .Comment: 31 pages, RevTeX, 4 figures appended as uuencoded fil
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