14,581 research outputs found
Natural SUSY: LHC and Dark Matter direct detection experiments interplay
Natural SUSY scenarios with a low value of the parameter, are
characterised by a higgsino-like dark matter candidate, and a compressed
spectrum for the lightest higgsinos. We explore the prospects for probing this
scenario at the 13 TeV stage of the LHC via monojet searches, with various
integrated luminosity options, and demonstrate how these results are affect by
different assumptions on the achievable level of control on the experimental
systematic uncertainties. The complementarity between collider and direct
detection experiments (present and future) is also highlighted.Comment: Proceeding for the 18th International Conference From the Planck
Scale to the Electroweak Scale (Ioannina, Greece, 25-29 May 2015
Positive and negative-parity flavor-octet baryons in coupled QCD sum rules
We apply the method of the QCD sum rule, in which positive- and
negative-parity baryons couple with each other, to the flavor-octet hyperons
and investigate the parity splittings. We also reexamine the nucleon in the
method, which was studied in our previous paper, by carefully choosing the
Borel weight. Both in the nucleon and hyperon channels the obtained sum rules
turn out to have a very good Borel stability and also have a Borel window, an
energy region in which the OPE converges and the pole contribution dominates
over the continuum contribution. The predicted masses of the positive- and
negative-parity baryons reproduce the experimental ones fairly well in the
and channels, if we assign the and the
to the parity partners of the and the ,
respectively. This implies that the is not the party partner of
the and may be a flavor-singlet or exotic state. In the
channel, the sum rule predicts the mass of the negative-parity state to be
about 1.8 GeV, which leads to two possibilities; one is that the observed state
with the closest mass, , is the parity partner and the other is that
the parity partner is not yet found but exists around 1.8 GeV.Comment: 15 pages, 4 figure
Decoherence Dynamics in Low-Dimensional Cold Atom Interferometers
We report on a study of the dynamics of decoherence of a matter-wave
interferometer, consisting of a pair of low-dimensional cold atom condensates
at finite temperature. We identify two distinct regimes in the time dependence
of the coherence factor of the interferometer: quantum and classical. Explicit
analytical results are obtained in both regimes. In particular, in the
two-dimensional (2D) case in the classical (long time) regime, we find that the
dynamics of decoherence is universal, exhibiting a power-law decay with an
exponent, proportional to the ratio of the temperature to the
Kosterlitz-Thouless temperature of a single 2D condensate. In the
one-dimensional (1D) case in the classical regime we find a universal
nonanalytic time dependence of decoherence, which is a consequence of the
nonhydrodynamic nature of damping in 1D liquids.Comment: 4 pages, published versio
Perturbation of a lattice spectral band by a nearby resonance
A soluble model of weakly coupled "molecular" and "nuclear" Hamiltonians is
studied in order to exhibit explicitly the mechanism leading to the enhancement
of fusion probability in case of a narrow near-threshold nuclear resonance. We,
further, consider molecular cells of this type being arranged in lattice
structures. It is shown that if the real part of the narrow nuclear resonance
lies within the molecular band generated by the intercellular interaction, an
enhancement, proportional to the inverse width of the nuclear resonance, is to
be expected.Comment: RevTeX, 2 figures within the file. In May 2000 the title changed and
some minor corrections have been don
Yukawa Coupling Unification in Supersymmetric Models
We present an updated assessment of the viability of t-b-tau Yukawa coupling
unification in supersymmetric models. For the superpotential Higgs mass
parameter mu>0, we find unification to less than 1% is possible, but only for
GUT scale scalar mass parameter m_{16}~8-20 TeV, and small values of gaugino
mass m_{1/2}<400 GeV. Such models require that a GUT scale mass splitting
exists amongst Higgs scalars with m_{H_u}^2<m_{H_d}^2. Viable solutions lead to
a radiatively generated inverted scalar mass hierarchy, with third generation
and Higgs scalars being lighter than other sfermions. These models have very
heavy sfermions, so that unwanted flavor changing and CP violating SUSY
processes are suppressed, but may suffer from some fine-tuning requirements.
While the generated spectra satisfy b->s gamma and (g-2)_mu constraints, there
exists tension with the dark matter relic density unless m_{16}<3 TeV. These
models offer prospects for a SUSY discovery at the Fermilab Tevatron collider
via the search for chargino_1 neutralino_2 -> 3 leptons events, or via gluino
pair production. If mu<0, Yukawa coupling unification to less than 5% can occur
for m_{16} and m_{1/2}>1-2 TeV. Consistency of negative mu Yukawa unified
models with b->s gamma, (g-2)_mu, and relic density all imply very large values
of m_{1/2} typically greater than about 2.5 TeV, in which case direct detection
of sparticles may be a challenge even at the LHC.Comment: 38 pages, 15 figures. Fig.15 changed, some references were added. A
copy of the paper with better resolution figures can be found at
http://www.hep.fsu.edu/~balazs/Physics/Papers/2003
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
Production of Z' and W' via Drell-Yan processes in the 4D Composite Higgs Model at the LHC
We present an analysis of both the Neutral Current (NC) and Charged Current
(CC) Drell-Yan processes at the LHC within a 4 Dimensional realization of a
Composite Higgs model studying the cross sections and taking into account the
possible impact of the extra fermions present in the spectrum.Comment: Conference proceeding, XII IFAE Edition, 3-5 April 2013, Cagliari. 2
pages, 2 figures; v2 typo correcte
The cranking formula and the spurious behaviour of the mass parameters
We discuss some aspects of the approach of the mass parameters by means of
the simple cranking model. In particular, it is well known that the numerical
application of this formula is often subject to ambiguities or contradictions.
It is found that these problems are induced by the presence of two derivatives
in the formula. To overcome these problems, we state a useful ansatz and we
develop a number of simple arguments which tend to justify the removal of these
terms. As soon as this is done, the formula becomes simpler and easier to
interpret. In this respect, it is shown how the shell effects affect the mass
parameters. A number of numerical tests help us in our conclusions.Comment: version 3 corrigendum of the ansatz of section V, corrigendum of the
legend of Fig3. Submission = text file + 5 figure
Noise and Transport Characterization of Single Molecular Break Junctions with Individual Molecule
We studied the noise spectra of molecule-free and molecule-containing
mechanically controllable break junctions. Both types of junctions revealed
typical 1/ f noise characteristics at different distances between the contacts
with square dependence of current noise power spectral density on current.
Additional Lorentzian-shape (1/ f 2) noise components were recorded only when
nanoelectrodes were bridged by individual 1,4 benzenediamine molecule. The
characteristic frequency of the revealed 1/ f 2 noise related to a single
bridging molecule correlates with the lock-in current amplitudes. The recorded
behavior of Lorentzian-shape noise component as a function of current is
interpreted as the manifestation of a dynamic reconfiguration of molecular
coupling to the metal electrodes. We propose a phenomenological model that
correlates the charge transport via a single molecule with the reconfiguration
of its coupling to the metal electrodes. Experimentally obtained results are in
good agreement with theoretical ones and indicate that coupling between the
molecule metal electrodes is important aspect that should be taken into
account.Comment: 15 pages, 7 figure
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