8,423 research outputs found
Leptoquark Single and Pair production at LHC with CalcHEP/CompHEP in the complete model
We study combined leptoquark (LQ) single and pair production at LHC at the
level of detector simulation. A set of kinematical cuts has been worked out to
maximize significance for combined signal events.
It was shown that combination of signatures from LQ single and pair
production not only significantly increases the LHC reach, but also allows us
to give the correct signal interpretation. In particular, it was found that the
LHC has potential to discover LQ with a mass up to 1.2 TeV and 1.5 TeV for the
case of scalar and vector LQ, respectively, and LQ single production
contributes 30-50% to the total signal rate for LQ-l-q coupling, taken equal to
the electromagnetic coupling.
This work is based on implementation of the most general form of scalar and
vector LQ interactions with quarks and gluons into CalcHEP/CompHEP packages.
This implementation, which authors made publicly available, was one the most
important aspects of the study.Comment: LaTeX, 27 pages, 15 figure
A to Z of the Muon anomalous magnetic moment in the MSSM with Pati-Salam at the GUT scale
We analyse the low energy predictions of the minimal supersymmetric standard model (MSSM) arising from a GUT scale Pati-Salam gauge group further constrained by an A4 × Z5 family symmetry, resulting in four soft scalar masses at the GUT scale: one left-handed soft mass m0 and three right-handed soft masses m1, m2, m3, one for each generation. We demonstrate that this model, which was initially developed to describe the neutrino sector, can explain collider and non-collider measurements such as the dark matter relic density, the Higgs boson mass and, in particular, the anomalous magnetic moment of the muon (g − 2)μ. Since about two decades, (g − 2)μ suffers a puzzling about 3σ excessoftheexperimentallymeasuredvalueoverthetheoreticalprediction,whichour model is able to fully resolve. As the consequence of this resolution, our model predicts specific regions of the parameter space with the specific properties including light smuons and neutralinos, which could also potentially explain di-lepton excesses observed by CMS and ATLAS
Hydrodynamic Modes in a Trapped Strongly Interacting Fermi Gases of Atoms
The zero-temperature properties of a dilute two-component Fermi gas in the
BCS-BEC crossover are investigated. On the basis of a generalization of the
variational Schwinger method, we construct approximate semi-analytical formulae
for collective frequencies of the radial and the axial breathing modes of the
Fermi gas under harmonic confinement in the framework of the hydrodynamic
theory. It is shown that the method gives nearly exact solutions.Comment: 11 page
Resonant nuclear transition in the d-mu-Li6 muonic molecule
The reaction rate of the nuclear fusion d+Li6 ----> Be8*(2+,0) is estimated
in the case where the nuclei are confined to each other by a muon. For the
description of nuclear transitions, a method which is analogous to the Linear
Combination of Atomic Orbitals has been used. Using the complex coordinate
rotation method, we found that a molecular d-mu-Li6 state exists with energy
(-20.3084-i0.0066) eV and |\Psi_{m}(0)|=0.44x10^{-7} fm^-3/2. The nuclear wave
functions needed, were constructed in the form of antisymmetrized products of
harmonic-oscillator functions for the three-cluster approximation, (dd\alpha),
to the five-body (NNNN\alpha) problem. It was found that the reaction rate
\lambda is strongly dependent on the energy gap between the d-Li6 threshold and
the energy of the final Be8^* resonant state. The value of \lambda obtained by
averaging over the width of this resonance, is 0.183x10^10 sec^{-1}.Comment: REVTEX, 63K, no postscripts, 21 pages, submitted to Phys.Rev.
Flavour SU(3) Symmetry in Charmless B Decays
QCD sum rules are used to estimate the flavour SU(3)-symmetry violation in
two-body B decays to pions and kaons. In the factorizable amplitudes the
SU(3)-violation manifests itself in the ratio of the decay constants f_K/f_pi
and in the differences between the B->K, B_s->K and B->pi form factors. These
effects are calculated from the QCD two-point and light-cone sum rules,
respectively, in terms of the strange quark mass and the ratio of the strange
and nonstrange quark-condensate densities. Importantly, QCD sum rules predict
that SU(3) breaking in the heavy-to-light form factors can be substantial and
does not vanish in the heavy-quark mass limit. Furthermore, we investigate the
strange-quark mass dependence of nonfactorizable effects in the B->K pi decay
amplitudes. Taking into account these effects we estimate the accuracy of
several SU(3)-symmetry relations between charmless B-decay amplitudes.Comment: Two references added, version to be published in Phys.Rev.D, 21
pages, 12 postscript figure
pp -> ttH, H->tau tau: toward a model independent determination of the Higgs boson couplings at the LHC
The possibility of detecting a Higgs boson through several production and
decay channels is instrumental to the measurement of its couplings. In this
paper we study the pp-> ttH(H-> tau tau) channel at the LHC, for the case of a
scalar Higgs boson, and use the obtained results to improve on existing
strategies toward a model independent determination of the Higgs boson
couplings. The case of a scalar Higgs boson with mass below 140 GeV looks
particularly promising.Comment: 19 pages, 5 Figures, LaTex, published version, typos corrected,
comments added in Sec.
Predictions on , and from QCD Light-Cone Sum Rules
The form factors of the , and transitions
are calculated from QCD light-cone sum rules (LCSR) and used to predict the
widths and differential distributions of the exclusive semileptonic decays
, and ,
where . The current theoretical uncertainties are estimated. The LCSR
results are found to agree with the results of lattice QCD calculations and
with experimental data on exclusive semileptonic D decays. Comparison of the
LCSR prediction on with the CLEO measurement yields a
value of |V_{ub}| in agreement with other determinations.Comment: 24 pages, 12 figures, Latex, epsfig, some additional remarks on the
two-pole parameterization, prediction on the form factor added,
version to appear in Phys. Rev.
Unbiased analysis of CLEO data at NLO and pion distribution amplitude
We discuss different QCD approaches to calculate the form factor
F^{\gamma^*\gamma\pi}(Q^2) of the \gamma^*\gamma\to\pi^{0} transition giving
preference to the light-cone QCD sum rules (LCSR) approach as being the most
adequate. In this context we revise the previous analysis of the CLEO
experimental data on F^{\gamma^*\gamma\pi}(Q^{2}) by Schmedding and Yakovlev.
Special attention is paid to the sensitivity of the results to the (strong
radiative) \alpha_s-corrections and to the value of the twist-four coupling
\delta^2. We present a full analysis of the CLEO data at the NLO level of
LCSRs, focusing particular attention to the extraction of the relevant
parameters to determine the pion distribution amplitude, i.e., the Gegenbauer
coefficients a_2 and a_4. Our analysis confirms our previous results and also
the main findings of Schmedding and Yakovlev: both the asymptotic, as well as
the Chernyak--Zhitnitsky pion distribution amplitudes are completely excluded
by the CLEO data. A novelty of our approach is to use the CLEO data as a means
of determining the value of the QCD vacuum non-locality parameter \lambda^2_q =
/ =0.4 GeV^2, which specifies the average virtuality of
the vacuum quarks.Comment: 25 pages, 5 figures, 4 tables; format and margins corrected to fit
page size; small changes in the text and correction of misprint
Universal Torsion-Induced Interaction from Large Extra Dimensions
We consider the Kaluza-Klein (KK) scenario in which only gravity exists in
the bulk. Without the assumption of symmetric connection, the presence of brane
fermions induces torsion. The result is a universal axial contact interaction
that dominates those induced by KK gravitons. This enhancement arises from a
large spin density on the brane. Using a global fit to Z-pole observables, we
find the 3 sigma bound on the scale of quantum gravity to be 28 TeV for n=2. If
Dirac or light sterile neutrinos are present, the data from SN1987A increase
the bound to \sqrt{n}M_S >= 210 TeV.Comment: 9 pages REVTeX, 1 postscript figure, uses axodraw.st
Heavy to Light Meson Exclusive Semileptonic Decays in Effective Field Theory of Heavy Quark
We present a general study on exclusive semileptonic decays of heavy (B, D,
B_s) to light (pi, rho, K, K^*) mesons in the framework of effective field
theory of heavy quark. Transition matrix elements of these decays can be
systematically characterized by a set of wave functions which are independent
of the heavy quark mass except for the implicit scale dependence. Form factors
for all these decays are calculated consistently within the effective theory
framework using the light cone sum rule method at the leading order of 1/m_Q
expansion. The branching ratios of these decays are evaluated, and the heavy
and light flavor symmetry breaking effects are investigated. We also give
comparison of our results and the predictions from other approaches, among
which are the relations proposed recently in the framework of large energy
effective theory.Comment: 18 pages, ReVtex, 5 figures, added references and comparison of
results, and corrected signs in some formula
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