18,310 research outputs found
Neutralino Proton Cross Sections in SUGRA and D-BRANE Models
We calculate the spin independent neutralino-proton cross section for
universal SUGRA, non universal SUGRA and D-brane models with R-parity
invariance. The regions of maximum cross section in these models has started to
be probed by the current detectors. The minimum cross section generally is
>~1\times 10^{-(9-10)}pb and hence will be accessible in the future detectors,
barring special regions of parameter space where it can reduce to =~10^{-12}pb.
However, the squarks and gluinos will be heavy (>~1 TeV) in the latter case,
but still accessible at the LHC.Comment: 3 pages, latex, 3 figures, talk at DPF 2000, Columbus, OH, August
9-12, 200
A new perspective on the relation between dark energy perturbations and the late-time ISW effect
The effect of quintessence perturbations on the ISW effect is studied for a
mixed dynamical scalar field dark energy (DDE) and pressureless perfect fluid
dark matter. A new and general methodology is developed to track the growth of
the perturbations, which uses only the equation of state (EoS) parameter
of the scalar field DDE,
and the initial values of the the relative entropy perturbation (between the
matter and DDE) and the intrinsic entropy perturbation of the scalar field DDE
as inputs. We also derive a relation between the rest frame sound speed
of an arbitrary DDE component and its EoS . We show that the ISW signal differs from that expected in a
CDM cosmology by as much as +20% to -80% for parameterizations of
consistent with SNIa data, and about 20% for
parameterizations of consistent with SNIa+CMB+BAO data, at 95%
confidence. Our results indicate that, at least in principle, the ISW effect
can be used to phenomenologically distinguish a cosmological constant from DDE.Comment: Accepted for publication at PR
Adiabatic multicritical quantum quenches: Continuously varying exponents depending on the direction of quenching
We study adiabatic quantum quenches across a quantum multicritical point
(MCP) using a quenching scheme that enables the system to hit the MCP along
different paths. We show that the power-law scaling of the defect density with
the rate of driving depends non-trivially on the path, i.e., the exponent
varies continuously with the parameter that defines the path, up to a
critical value ; on the other hand for , the scaling exponent saturates to a constant value. We show that
dynamically generated and {\it path()-dependent} effective critical
exponents associated with the quasicritical points lying close to the MCP (on
the ferromagnetic side), where the energy-gap is minimum, lead to this
continuously varying exponent. The scaling relations are established using the
integrable transverse XY spin chain and generalized to a MCP associated with a
-dimensional quantum many-body systems (not reducible to two-level systems)
using adiabatic perturbation theory. We also calculate the effective {\it
path-dependent} dimensional shift (or the shift in center of the
impulse region) that appears in the scaling relation for special paths lying
entirely in the paramagnetic phase. Numerically obtained results are in good
agreement with analytical predictions.Comment: 5 pages, 4 figure
Critical dynamics of nonconserved -vector model with anisotropic nonequilibrium perturbations
We study dynamic field theories for nonconserving -vector models that are
subject to spatial-anisotropic bias perturbations. We first investigate the
conditions under which these field theories can have a single length scale.
When N=2 or , it turns out that there are no such field theories, and,
hence, the corresponding models are pushed by the bias into the Ising class. We
further construct nontrivial field theories for N=3 case with certain bias
perturbations and analyze the renormalization-group flow equations. We find
that the three-component systems can exhibit rich critical behavior belonging
to two different universality classes.Comment: Included RG analysis and discussion on new universality classe
Mixed Phase in Compact Starts : M-R relations and radial oscillations
It is believed that quark stars or neutron stars with mixed phase in the core
have smaller radii compared to ordinary compact stars. With the recent
observation of several low radius objects, typically a radius of for
star of mass in low mass X-ray binaries (LMXB), it has become very
important to understand the nature of these objects. An accurate determination
of mass-radius relationship of these objects provide us with a physical
laboratory to study the composition of high density matter and the nature of
phase transition. We study the effect of quark and nuclear matter mixed phase
on mass radius relationship and radial oscillations of neutron stars. We find
that the effect of the mixed phase is to decrease the maximum mass of a stable
neutron star and to decrease the radial frequencies .Comment: guest contribution at Int. Workshop on Astronomy & Relativistic
Astrophysics (IWARA 03)held at Olinda-PE (Brazil) from Oct. 12-17,200
Phase transitions in periodically driven macroscopic systems
We study the large-time behavior of a class of periodically driven
macroscopic systems. We find, for a certain range of the parameters of either
the system or the driving fields, the time-averaged asymptotic behavior
effectively is that of certain other equilibrium systems. We then illustrate
with a few examples how the conventional knowledge of the equilibrium systems
can be made use in choosing the driving fields to engineer new phases and to
induce new phase transitions.Comment: LaTex, 8 page
Ab initio explanation of disorder and off-stoichiometry in Fe-Mn-Al-C kappa carbides
Carbides play a central role for the strength and ductility in many
materials. Simulating the impact of these precipitates on the mechanical
performance requires the knowledge about their atomic configuration. In
particular, the C content is often observed to substantially deviate from the
ideal stoichiometric composition. In the present work, we focus on Fe-Mn-Al-C
steels, for which we determined the composition of the nano-sized kappa
carbides (Fe,Mn)3AlC by atom probe tomography (APT) in comparison to larger
precipitates located in grain boundaries. Combining density functional theory
with thermodynamic concepts, we first determine the critical temperatures for
the presence of chemical and magentic disorder in these carbides. Secondly, the
experimentally observed reduction of the C content is explained as a compromise
between the gain in chemical energy during partitioning and the elastic strains
emerging in coherent microstructures
Microwave Near-Field Imaging of Electric Fields in a Superconducting Microstrip Resonator
We describe the use of a cryogenic near-field scanning microwave microscope
to image microwave electric fields from superconducting and normal-metal
microstrip resonators. The microscope employs an open-ended coaxial probe and
operates from 77 to 300 K in the 0.01-20 GHz frequency range with a spatial
resolution of about 200 mm. We describe the operation of the system and present
microwave images of Cu and Tl2Ba2CaCu2O8 microstrip resonators, showing
standing wave patterns at the fundamental and second harmonic frequencies.Comment: 9 pages, 3 eps figure
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