777 research outputs found
Spinning particle in an external linearized gravitational wave field
We study the interaction of a scalar and a spinning particle with a coherent
linearized gravitational wave field treated as a classical spin two external
field. The spin degrees of freedom of the spinning particle are described by
skew-commuting variables. We derive the explicit expressions for the
eigenfunctions and the Green's functions of the theory. The discussion is exact
within the approximation of neglecting radiative corrections and we prove that
the result is completely determined by the semiclassical contribution.Comment: 11 page
Ladder-QCD at finite isospin chemical potential
We use an effective QCD model (ladder-QCD) to explore the phase diagram for
chiral symmetry breaking and restoration at finite temperature with different
quark chemical potentials. In agreement with a recent investigation based
on the Nambu-Jona-Lasinio model, we find that a finite pion condensate shows up
for high enough isospin chemical potential . For
small the phase diagram in the plane shows two first
order transition lines and two critical ending points.Comment: Typed in RevTex4, pages 12, figures 2. Two references adde
Particles with anomalous magnetic moment in external e.m. fields: the proper time formulation
In this paper we evaluate the expression for the Green function of a
pseudo-classical spinning particle interacting with constant electromagnetic
external fields by taking into account the anomalous magnetic and electric
moments of the particle. The spin degrees of freedom are described in terms of
Grassmann variables and the evolution operator is obtained through the
Fock-Schwinger proper time method.Comment: 10 page
Relativistic two-body calculation of -mesons radiative decays
This paper is a prosecution of a previous work where we presented a unified
two-fermion covariant scheme which produced very precise results for the masses
of light and heavy mesons. We extend the analysis to some radiative decays of
mesons and we
calculate their branching ratios and their widths. For most of them we can make
a comparison with experimental data finding a good agreement.For the decays for
which data are not available we compare ours with other recent theoretical
previsions.Comment: 7 pages, 1 figur
A calculation of the QCD phase diagram at finite temperature, and baryon and isospin chemical potentials
We study the phases of a two-flavor Nambu-Jona-Lasinio model at finite
temperature , baryon and isospin chemical potentials:
, . This study
completes a previous analysis where only small isospin chemical potentials
were consideredComment: 21 pages, 13 figures included, two more refernces adde
Constraints on top quark non-standard interactions from Higgs and production cross sections
We identify the differential cross sections for production and the
total cross section for Higgs production through gluon fusion as the processes
in which the two effective operators describing the leading non-standard
interactions of the top quark with the gluon can be disentangled and studied in
an independent fashion. Current data on the Higgs production and the differential cross section provide limits comparable,
but not more stringent, than those from the total cross sections
measurements at the LHC and Tevatron, where however the two operators enter on
the same footing and can only be constrained together. Given the present
uncertainties, we find that the most stringent bounds are provided by a
combination of data on the total cross sections together with those
from the Higgs production. We conclude by stating the (modest) reduction in the
uncertainties necessary to provide more stringent limits by means of the Higgs
production and differential cross section observables at the LHC with
the future luminosity of 300 and 3000 fb.Comment: 12 pages, 9 figures, 3 tables. Discussion with the relation of the
considered operators with the ones of the Warsaw basis extended. Missing
contribution to the gluon fusion amplitude added. Main results unchange
Dirac Fields on Spacelike Hypersurfaces, Their Rest-Frame Description and Dirac Observables
Grassmann-valued Dirac fields together with the electromagnetic field (the
pseudoclassical basis of QED) are reformulated on spacelike hypersurfaces in
Minkowski spacetime and then restricted to Wigner hyperplanes to get their
description in the rest-frame Wigner-covariant instant form of dynamics. The
canonical reduction to the Wigner-covariant Coulomb gauge is done in the rest
frame. It is shown, on the basis of a geometric incosistency, that the
description of fermions is incomplete, because there is no bosonic carrier of
the spin structure describing the trajectory of the electric current in
Minkowski spacetime, as it was already emphasized in connection with the first
quantization of spinning particles in a previous paper.Comment: 44 pages, revte
Status and prospects of the nMSSM after LHC Run-1
The new minimal supersymmetric standard model (nMSSM), a variant of the
general next to minimal supersymmetric standard model (NMSSM) without
symmetry, features a naturally light singlino with a mass below 75 GeV. In
light of the new constraints from LHC Run-1 on the Higgs couplings, sparticles
searches and flavour observables, we define the parameter space of the model
which is compatible with both collider and dark matter (DM) properties. Among
the regions compatible with these constraints, implemented through NMSSMTools,
SModelS and MadAnalysis 5, only one with a singlino lightest supersymmetric
particle (LSP) with a mass around 5 GeV can explain all the DM abundance of the
universe, while heavier mixed singlinos can only form one of the DM components.
Typical collider signatures for each region of the parameter space are
investigated. In particular, the decay of the 125 GeV Higgs into light scalars
and/or pseudoscalars and the decay of the heavy Higgs into charginos and
neutralinos, provide distinctive signatures of the model. Moreover, the
sfermion decays usually proceed through heavier neutralinos rather than
directly into the LSP, as the couplings to the singlino are suppressed. We also
show that direct detection searches are complementary to collider ones, and
that a future ton-scale detector could completely probe the region of parameter
space with a LSP mass around 65 GeV.Comment: 33 pages, 9 figures. Version accepted for publication in JHE
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