614 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
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
Foldy-Wouthuysen Transformation for a Spinning Particle with Anomalous Magnetic Moment
We study the Foldy-Wouthuysen transformation for a pseudoclassical particle
with anomalous magnetic moment in an external, stationary electromagnetic
field. We show that the transformation can be expressed in a closed form for
neutral particles in purely electrostatic fields and for neutral and charged
particles in external magnetostatic fields. The explicit expressions of the
diagonalized Hamiltonians are calculated.Comment: 10 page
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
Spinning Particle with Anomalous Magnetic Moment in an External Plane Wave Field
In this paper we study the interaction of a Dirac-Pauli particle with an
electromagnetic plane wave, by using a previously given generalization of the
pseudo-classical Lagrangian for a spinning particle with an anomalous magnetic
moment. We derive the explicit expressions for the eigenfunctions and the
Green's functions of the theory. We discuss the validity of the semi-classical
approach by comparing the wavefunctions with the (pseudo)-classical solutions
of the Hamilton-Jacobi equation.Comment: 10 page
Multiple Z' -> t-tbar signals in a 4D Composite Higgs Model
We study the production of top-antitop pairs at the Large Hadron Collider as
a testbed for discovering heavy Z' bosons belonging to a composite Higgs model,
as, in this scenario, such new gauge interaction states are sizeably coupled to
the third generation quarks of the Standard Model. We study their possible
appearance in cross section as well as (charge and spin) asymmetry
distributions. Our calculations are performed in the minimal four-dimensional
formulation of such a scenario, namely the 4-Dimensional Composite Higgs Model
(4DCHM), which embeds five new s. We pay particular attention to the case
of nearly degenerate resonances, highlighting the conditions under which these
are separable in the aforementioned observables. We also discuss the impact of
the intrinsic width of the new resonances onto the event rates and various
distributions. We confirm that the 14 TeV stage of the LHC will enable one to
detect two such states, assuming standard detector performance and machine
luminosity. A mapping of the discovery potential of the LHC of these new gauge
bosons is given. Finally, from the latter, several benchmarks are extracted
which are amenable to experimental investigation.Comment: 30 pages, 3 figures. Text and figures updated to match published
versio
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
A large Nc perspective on the QCD phase diagram
The transition between the hadronic phase and the quark gluon plasma phase at
nonzero temperature and quark chemical potentials is studied within the
large-Nc expansion of QCD.Comment: 5 page
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