2,928 research outputs found
Tripletless unification in the conformal window
A product SU(5)xSp(4) grand unified model is proposed with no fundamental
Higgs fields transforming under SU(5). Higgs doublets are instead embedded into
a four dimensional representation of the Sp(4) gauge group, and hence there is
no doublet-triplet splitting problem because there are no triplets. The Sp(4)
group contains enough matter to lie in the conformal window, causing its gauge
coupling to flow to a strongly-coupled infrared fixed-point at low energy,
naturally preserving gauge coupling unification to percent level accuracy.
Yukawa couplings, including the top, arise through dimension five operators
that are enhanced by the large anomalous dimension of the Higgs fields. Proton
decay mediated by dimension five operators is absent at the perturbative level.
It reappears, however, non-perturbatively due to Sp(4) instantons but the rate
is suppressed by a high power of the ratio of the dynamical scale to the
unification scale. With gravity- or gaugino-mediated supersymmetry breaking,
non-universal gaugino masses are predicted, satisfying specific one-loop
renormalization group invariant relations. These predictions should be easily
testable with the LHC and a linear collider.Comment: 15 pages, 1 figur
Models of Neutrino Mass with a Low Cutoff Scale
In theories with a low quantum gravity scale, global symmetries are expected
to be violated, inducing excessive proton decay or large Majorana neutrino
masses. The simplest cure is to impose discrete gauge symmetries, which in turn
make neutrinos massless. We construct models that employ these gauge symmetries
while naturally generating small neutrino masses. Majorana (Dirac) neutrino
masses are generated through the breaking of a discrete (continuous) gauge
symmetry at low energies, e.g., 2 keV to 1 GeV. The Majorana case predicts
\Delta N_\nu \simeq 1 at BBN, neutrinoless double beta decay with scalar
emission, and modifications to the CMB anisotropies from domain walls in the
universe as well as providing a possible Dark Energy candidate. For the Dirac
case, despite the presence of a new light gauge boson, all laboratory,
astrophysical, and cosmological constraints can be avoided.Comment: 11 pages, 4 figure
Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature
We present a high-resolution microwave spectrometer to measure the
frequency-dependent complex conductivity of a superconducting thin film near
the critical temperature. The instrument is based on a broadband measurement of
the complex reflection coefficient, , of a coaxial transmission
line, which is terminated to a thin film sample with the electrodes in a
Corbino disk shape. In the vicinity of the critical temperature, the standard
calibration technique using three known standards fails to extract the strong
frequency dependence of the complex conductivity induced by the superconducting
fluctuations. This is because a small unexpected difference between the phase
parts of for a short and load standards gives rise to a large
error in the detailed frequency dependence of the complex conductivity near the
superconducting transition. We demonstrate that a new calibration procedure
using the normal-state conductivity of a sample as a load standard resolves
this difficulty. The high quality performance of this spectrometer, which
covers the frequency range between 0.1 GHz and 10 GHz, the temperature range
down to 10 K, and the magnetic field range up to 1 T, is illustrated by the
experimental results on several thin films of both conventional and high
temperature superconductors.Comment: 13 pages, 14 figure
Spectral-Function Sum Rules in Supersymmetry Breaking Models
The technique of Weinberg's spectral-function sum rule is a powerful tool for
a study of models in which global symmetry is dynamically broken. It enables us
to convert information on the short-distance behavior of a theory to relations
among physical quantities which appear in the low-energy picture of the theory.
We apply such technique to general supersymmetry breaking models to derive new
sum rules.Comment: 18 pages, 1 figur
Mutual information and self-control of a fully-connected low-activity neural network
A self-control mechanism for the dynamics of a three-state fully-connected
neural network is studied through the introduction of a time-dependent
threshold. The self-adapting threshold is a function of both the neural and the
pattern activity in the network. The time evolution of the order parameters is
obtained on the basis of a recently developed dynamical recursive scheme. In
the limit of low activity the mutual information is shown to be the relevant
parameter in order to determine the retrieval quality. Due to self-control an
improvement of this mutual information content as well as an increase of the
storage capacity and an enlargement of the basins of attraction are found.
These results are compared with numerical simulations.Comment: 8 pages, 8 ps.figure
Stability of Intercelular Exchange of Biochemical Substances Affected by Variability of Environmental Parameters
Communication between cells is realized by exchange of biochemical
substances. Due to internal organization of living systems and variability of
external parameters, the exchange is heavily influenced by perturbations of
various parameters at almost all stages of the process. Since communication is
one of essential processes for functioning of living systems it is of interest
to investigate conditions for its stability. Using previously developed
simplified model of bacterial communication in a form of coupled difference
logistic equations we investigate stability of exchange of signaling molecules
under variability of internal and external parameters.Comment: 11 pages, 3 figure
The Phase Structure of Supersymmetric Sp(2N_c) Gauge Theories with an Adjoint
We study the phase structure of N = 1 supersymmetric Sp(2N_c) gauge theories
with 2N_f fundamentals, an adjoint, and vanishing superpotential. Using
a-maximization, we derive analytic expressions for the values of N_f below
which the first several gauge-invariant operators in the chiral ring violate
the unitarity bound and become free fields. In doing so we are able to
explicitly check previous conjectures about the behavior of this theory made by
Luty, Schmaltz, and Terning. We then compare this to an analysis of the first
two 'deconfined' dual descriptions based on the gauge groups Sp(2N_f+2) x
SO(2N_c+5) and Sp(2N_f+2) x SO(4N_f+4) x Sp(2N_c+2), finding precise agreement.
In particular, we find no evidence for non-obvious accidental symmetries or the
appearance of a mixed phase in which one of the dual gauge groups becomes free.Comment: 18 pages, 2 figures; v2: added references to match JHEP versio
Geometry of One-Dimensional Wave Propagation
We investigate the geometrical features of one-dimensional wave propagation,
whose dynamics is described by the (2+1)-dimensional Lorentz group. We find
many interesting geometrical ingredients such as spinorlike behavior of wave
amplitudes, gauge transformations, Bloch-type equations, and Lorentz-group
Berry phases. We also propose an optical experiment to verify these effects.Comment: RevTeX, 16 pages, 6 postscript figure
Gravitational Baryogenesis
We show that a gravitational interaction between the derivative of the Ricci
scalar curvature and the baryon-number current dynamically breaks CPT in an
expanding universe and, combined with baryon-number-violating interactions, can
drive the universe towards an equilibrium baryon asymmetry that is
observationally acceptable.Comment: Revtex4, 4 pages, two figure
Modeling of Viscous Shock Tube Using ES-BGK Model Kinetic Equations
The viscous effects on unsteady shock wave propagation are investigated by numerical solution of the Boltzmann model kinetic equations. The kinetic equations are solved for two unsteady non-equilibrium flow problems, namely, the one-dimensional Riemann problem and a two-dimensional viscous shock-tube. The numerical method comprises the discrete velocity method in the velocity space and the finite volume discretization in physical space using various flux schemes. The discrete version of H-theorem is applied for analysis of accuracy of the numerical solution as well as of the onset of non-equilibrium. Simulations show that the maximum entropy generation rate in viscous shock tube occurs in the boundary layer / shock wave interaction region. The entropy generation rate is used to determine the time-variation of the speed of propagation of shock, contact discontinuity and rarefaction waves
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