4,730 research outputs found
Collapses and revivals of stored orbital angular momentum of light in a cold atomic ensemble
We report on the storage of orbital angular momentum of light in a cold
ensemble of cesium atoms. We employ Bragg diffraction to retrieve the stored
optical information impressed into the atomic coherence by the incident light
fields. The stored information can be manipulated by an applied magnetic field
and we were able to observe collapses and revivals due to the rotation of the
stored atomic Zeeman coherence for times longer than 15 .Comment: Submitted to Physical Review
Dynamics of a stored Zeeman coherence grating in an external magnetic field
We investigate the evolution of a Zeeman coherence grating induced in a cold
atomic cesium sample in the presence of an external magnetic field. The
gratings are created in a three-beam light storage configuration using two
quasi-collinear writing laser pulses and reading with a counterpropagating
pulse after a variable time delay. The phase conjugated pulse arising from the
atomic sample is monitored. Collapses and revivals of the retrieved pulse are
observed for different polarizations of the laser beams and for different
directions of the applied magnetic field. While magnetic field inhomogeneities
are responsible for the decay of the coherent atomic response, a five-fold
increase in the coherence decay time, with respect to no applied magnetic
field, is obtained for an appropriate choice of the direction of the applied
magnetic field. A simplified theoretical model illustrates the role of the
magnetic field mean and its inhomogeneity on the collective atomic response.Comment: To appear in J. Phys.
Double Higgs production at TeV Colliders in the Minimal Supersymmetric Standard Model
The reconstruction of the Higgs potential in the Minimal Supersymmetric
Standard Model (MSSM) requires the measurement of the trilinear Higgs
self-couplings. The `double Higgs production' subgroup has been investigating
the possibility of detecting signatures of processes carrying a dependence on
these vertices at the Large Hadron Collider (LHC) and future Linear Colliders
(LCs). As reference reactions, we have chosen and ,
respectively, where is the lightest of the MSSM Higgs bosons. In both
cases, the interaction is involved. For , the two reactions are
resonant in the mode, providing cross sections which are detectable
at both accelerators and strongly sensitive to the strength of the trilinear
coupling involved. We explore this mass regime of the MSSM in the decay channel, also accounting for irreducible background effects.Comment: LaTeX, 23 pages, 13 PostScript figures (contribution to the Summary
Report of the Higgs WG, Workshop `Physics at TeV Colliders', Les Houches,
France, 8-18 June 1999): some modifications to the bibliograph
Euclidean Thermal Green Functions of Photons in Generalized Euclidean Rindler Spaces for any Feynman-like Gauge
The thermal Euclidean Green functions for Photons propagating in the Rindler
wedge are computed employing an Euclidean approach within any covariant
Feynman-like gauge. This is done by generalizing a formula which holds in the
Minkowskian case. The coincidence of the found (\be=2\pi)-Green functions and
the corresponding Minkowskian vacuum Green functions is discussed in relation
to the remaining static gauge ambiguity already found in previous papers.
Further generalizations to more complicated manifolds are discussed. Ward
identities are verified in the general case.Comment: 12 pages, standard latex, no figures, some signs changed, more
comments added, final version to appear on Int. J. Mod. Phys.
XQCAT: eXtra Quark Combined Analysis Tool
XQCAT (eXtra Quark Combined Analysis Tool) is a tool aimed at determining
exclusion confidence levels for scenarios of new physics characterised by the
presence of one or multiple heavy extra quarks which interact through Yukawa
couplings with any of the Standard Model quarks. The code uses a database of
efficiencies for pre-simulated processes of QCD-induced pair production of
extra quarks and their subsequent on-shell decays. In the version 1.2 of XQCAT
the efficiencies have been computed for a set of seven publicly available
search results by the CMS experiment. The input for the code is a text file in
which masses, branching ratios and dominant chirality of the couplings of the
new quarks are provided. The output of the code is the exclusion confidence
levels of the test point for each implemented experimental analysis considered
individually and, when possible, in statistical combination.Comment: 18 pages, 2 figures, version accepted for publication in Comp. Phys.
Comm., fixed formatting problems caused by the arXiv's autotex syste
Phenomenological Consequences of the Constrained Exceptional Supersymmetric Standard Model
The Exceptional Supersymmetric Standard Model (ESSM) provides a low
energy alternative to the MSSM, with an extra gauged U(1) symmetry, solving
the -problem of the MSSM. Inspired by the possible embedding into an E
GUT, the matter content fills three generations of E multiplets, thus
predicting exciting exotic matter such as diquarks or leptoquarks. We present
predictions from a constrained version of the model (cESSM), with a
universal scalar mass , trilinear mass and gaugino mass . We
reveal a large volume of the cESSM parameter space where the correct
breakdown of the gauge symmetry is achieved and all experimental constraints
satisfied. We predict a hierarchical particle spectrum with heavy scalars and
light gauginos, while the new exotic matter can be light or heavy depending on
parameters. We present representative cESSM scenarios, demonstrating that
there could be light exotic particles, like leptoquarks and a U(1) Z'
boson, with spectacular signals at the LHC.Comment: Contribution to the proceedings of SUSY 09, Boston, USA, June 2009, 4
page
Be Decay Anomaly and Light
In this proceedings, we discuss a light (17 MeV) solution to the anomaly
observed in the decay of Beryllium-8 by the Atomki collaboration. We detail an
anomaly free model with minimal particle content which can satisfy all other
experimental constraints with gauge couplings .Comment: Prepared for the 2019 EW session of the 54th Rencontres de Moriond,
talk presented by Simon Kin
Naturalness and Dark Matter Properties of the BLSSM
In this report, we compare the naturalness and Dark Matter (DM) properties of
the Minimal Supersymmetric Standard Model (MSSM) and the Supersymmetric
Standard Model (BLSSM), with universality in both cases. We do this by adopting
standard measures for the quantitative analysis of the Fine-Tuning (FT), at
both low (i.e. supersymmetric (SUSY)) and high (i.e. unification) scales. We
will see a similar level of FT for both models in these scenarios, with a
slightly better FT for the BLSSM at SUSY scales and MSSM at Grand Unification
Theory (GUT) scales. When including DM relic constraints, we drastically
confine the MSSM's parameter space, whereas we still find a large parameter
space available for the non-minimal scenario.Comment: Prepared for proceedings for DIS2017, talk presented by Simon Kin
LHC Signatures of the Constrained Exceptional Supersymmetric Standard Model
We discuss two striking Large Hadron Collider (LHC) signatures of the
constrained version of the exceptional supersymmetric standard model (cE6SSM),
based on a universal high energy soft scalar mass m_0, soft trilinear coupling
A_0 and soft gaugino mass M_{1/2}. The first signature we discuss is that of
light exotic colour triplet charge 1/3 fermions, which we refer to as
D-fermions. We calculate the LHC production cross section of D-fermions, and
discuss their decay patterns. Secondly we discuss the E6 type U(1)_N spin-1 Z'
gauge boson and show how it may decay into exotic states, increasing its width
and modifying the line shape of the dilepton final state. We illustrate these
features using two representative cE6SSM benchmark points, including an "early
LHC discovery" point, giving the Feynman rules and numerical values for the
relevant couplings in order to facilitate further studies.Comment: 30 pages, 5 figures, corrections to figure caption
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