44 research outputs found
Probing a Mixed Neutralino Dark Matter Model at the 7 TeV LHC
We have analyzed the prospect of probing a non-universal gaugino mass model
of mixed bino-higgsino dark matter at the current 7 TeV run of LHC. It provides
cosmologically compatible dark matter relic density over two broad bands of
parameters, corresponding to m_{\gl} < m_{\sq} and m_{\gl} \sim m_{\sq}.
The SUSY spectrum of this model has two distinctive features : (i) an
approximate degeneracy among the lighter chargino and neutralino masses, and
(ii) an inverted mass hierarchy of squark masses. We find that these features
can be exploited to obtain a viable signal upto m_{\gl} \sim 800 GeV over
both the parameter bands with an integrated luminosity 5/fb.Comment: Latex, 15 pages, one figur
Interplay between Josephson effect and magnetic interactions in double quantum dots
We analyze the magnetic and transport properties of a double quantum dot
coupled to superconducting leads. In addition to the possible phase transition
to a state, already present in the single dot case, this system exhibits
a richer magnetic behavior due to the competition between Kondo and inter-dot
antiferromagnetic coupling. We obtain results for the Josephson current which
may help to understand recent experiments on superconductor-metallofullerene
dimer junctions. We show that in such a system the Josephson effect can be used
to control its magnetic configuration.Comment: 5 pages, 4 figure
Stability of junction configurations in ferromagnet-superconductor heterostructures
We investigate the stability of possible order parameter configurations in
clean layered heterostructures of the type, where is a
superconductor and a ferromagnet. We find that for most reasonable values
of the geometric parameters (layer thicknesses and number) and of the material
parameters (such as magnetic polarization, wavevector mismatch, and oxide
barrier strength) several solutions of the {\it self consistent} microscopic
equations can coexist, which differ in the arrangement of the sequence of ``0''
and ``'' junction types (that is, with either same or opposite sign of the
pair potential in adjacent layers). The number of such coexisting self
consistent solutions increases with the number of layers. Studying the relative
stability of these configurations requires an accurate computation of the small
difference in the condensation free energies of these inhomogeneous systems. We
perform these calculations, starting with numerical self consistent solutions
of the Bogoliubov-de Gennes equations. We present extensive results for the
condensation free energies of the different possible configurations, obtained
by using efficient and accurate numerical methods, and discuss their relative
stabilities. Results for the experimentally measurable density of states are
also given for different configurations and clear differences in the spectra
are revealed. Comprehensive and systematic results as a function of the
relevant parameters for systems consisting of three and seven layers (one or
three junctions) are given, and the generalization to larger number of layers
is discussed.Comment: 17 pages, including 14 Figures. Higher resolution figures available
from the author
Dyson's Brownian Motion and Universal Dynamics of Quantum Systems
We establish a correspondence between the evolution of the distribution of
eigenvalues of a matrix subject to a random Gaussian perturbing
matrix, and a Fokker-Planck equation postulated by Dyson. Within this model, we
prove the equivalence conjectured by Altshuler et al between the space-time
correlations of the Sutherland-Calogero-Moser system in the thermodynamic limit
and a set of two-variable correlations for disordered quantum systems
calculated by them. Multiple variable correlation functions are, however, shown
to be inequivalent for the two cases.Comment: 10 pages, revte
Equivalent bosonic theory for the massive Thirring model with non-local interaction
We study, through path-integral methods, an extension of the massive Thirring
model in which the interaction between currents is non-local. By examining the
mass-expansion of the partition function we show that this non-local massive
Thirring model is equivalent to a certain non-local extension of the
sine-Gordon theory. Thus, we establish a non-local generalization of the famous
Coleman's equivalence. We also discuss some possible applications of this
result in the context of one-dimensional strongly correlated systems and
finite-size Quantum Field Theories.Comment: 15 pages, latex, no figure
Constraints on Quartic Vector-Boson Interactions from Z Physics
We obtain the constraints on possible anomalous quartic vector-boson vertices
arising from the precision measurements at the pole. In the framework of
chiral Lagrangians, we examine all effective operators
of order that lead to four-gauge-boson interactions but do not induce
anomalous trilinear vertices. We constrain the anomalous quartic interactions
by evaluating their one-loop corrections to the pole physics. Our analysis
is performed in a generic gauge and it shows that only the operators
that break the custodial symmetry get limits close to the theoretical
expectations. Our results also indicate that these anomalous couplings are
already out of reach of the Next Linear Collider, while the Large
Hadron Collider could be able to further extend the bounds on some of these
couplings.Comment: 16 pages, 1 Postscript figures, uses RevTex and eps.st
Current fluctuations of polymeric chains
Coherent electron transport is investigated in a molecular device made of
polymeric chain sandwiched between two metallic electrodes. Molecular system is
described by a simple Huckel model, while the coupling to the electrodes is
treated through the use of Newns-Anderson chemisorption theory. Transport
characteristics and noise power are calculated in two response regimes: linear
and nonlinear, respectively. Here is shown a strong dependence of the shot
noise on: (i) the length of the polymeric chain and (ii) the strength of the
molecule-to-electrodes coupling. In particular, detailed discussion of
Poissonian to sub-Poissonian crossover in the noise spectra is included.
Presented algorithm allows to calculate the lowest possible level of current
fluctuations (due to Pauli exclusion principle) in designing molecular devices.Comment: 8 pages, 5 figure
Supersymmetric Electroweak Renormalization of the Z-Width in the MSSM (I)
Within the framework of the MSSM, we compute the complete set of electroweak
one-loop supersymmetric quantum effects on the width of the
-boson in the on-shell renormalization scheme. Numerical analyses of the
corrections to the various partial widths into leptons and quarks are
presented. On general grounds, the average size of the electroweak SUSY
corrections to may well saturate the level of the present
theoretical uncertainties, even if considering the full supersymmetric spectrum
lying in the neighbourhood of the unaccessible LEP 200 range. Remarkably
enough, for the present values of the top quark mass, the electroweak SUSY
effects could be, globally, very close or even bigger than the electroweak SM
corrections, but opposite in sign. Therefore, in the absence of theoretical
errors, there are large regions of parameter space where one could find that,
effectively, the electroweak SM corrections are ``missing'', or even having the
``wrong'' sign. This should be helpful in discriminating between the SM and the
MSSM. However, an accurate prediction of the electroweak quantum effects on
will only be possible, if and are pinned down
in the future with enough precision.Comment: 17 p. in LaTeX. Preprint UAB-FT-343. Error in figure caption #3
corrected. Results unchange
New Precision Electroweak Tests of SU(5) x U(1) Supergravity
We explore the one-loop electroweak radiative corrections in supergravity via explicit calculation of vacuum-polarization and
vertex-correction contributions to the and
parameters. Experimentally, these parameters are obtained from a global fit to
the set of observables , and . We
include -dependent effects, which induce a large systematic negative shift
on for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). The
(non-oblique) supersymmetric vertex corrections to \Zbb, which define the
parameter, show a significant positive shift for light chargino
masses, which for can be nearly compensated by a negative
shift from the charged Higgs contribution. We conclude that at the 90\%CL, for
m_t\lsim160\GeV the present experimental values of and
do not constrain in any way supergravity in
both no-scale and dilaton scenarios. On the other hand, for m_t\gsim160\GeV
the constraints on the parameter space become increasingly stricter. We
demonstrate this trend with a study of the m_t=170\GeV case, where only a
small region of parameter space, with \tan\beta\gsim4, remains allowed and
corresponds to light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). Thus
supergravity combined with high-precision LEP data would
suggest the presence of light charginos if the top quark is not detected at the
Tevatron.Comment: LaTeX, 11 Pages+4 Figures(not included), the figures available upon
request as an uuencoded file(0.4MB) or 4 PS files from [email protected],
CERN-TH.7078/93, CTP-TAMU-68/93, ACT-24/9
Resonant hyper-Raman scattering in spherical quantum dots
A theoretical model of resonant hyper-Raman scattering by an ensemble of
spherical semiconductor quantum dots has been developed. The electronic
intermediate states are described as Wannier-Mott excitons in the framework of
the envelope function approximation. The optical polar vibrational modes of the
nanocrystallites (vibrons) and their interaction with the electronic system are
analized with the help of a continuum model satisfying both the mechanical and
electrostatic matching conditions at the interface. An explicit expression for
the hyper-Raman scattering efficiency is derived, which is valid for incident
two-photon energy close to the exciton resonances. The dipole selection rules
for optical transitions and Fr\"ohlich-like exciton-lattice interaction are
derived: It is shown that only exciton states with total angular momentum
and vibrational modes with angular momentum contribute to the
hyper-Raman scattering process. The associated exciton energies, wavefunctions,
and vibron frequencies have been obtained for spherical CdSe zincblende-type
nanocrystals, and the corresponding hyper-Raman scattering spectrum and
resonance profile are calculated. Their dependence on the dot radius and the
influence of the size distribution on them are also discussed.Comment: 12 pages REVTeX (two columns), 2 tables, 8 figure