288 research outputs found
Gravity Waves as a Probe of Hubble Expansion Rate During An Electroweak Scale Phase Transition
Just as big bang nucleosynthesis allows us to probe the expansion rate when
the temperature of the universe was around 1 MeV, the measurement of gravity
waves from electroweak scale first order phase transitions may allow us to
probe the expansion rate when the temperature of the universe was at the
electroweak scale. We compute the simple transformation rule for the gravity
wave spectrum under the scaling transformation of the Hubble expansion rate. We
then apply this directly to the scenario of quintessence kination domination
and show how gravity wave spectra would shift relative to LISA and BBO
projected sensitivities.Comment: 28 pages, 2 figures
Microcanonical entropy inflection points: Key to systematic understanding of transitions in finite systems
We introduce a systematic classification method for the analogs of phase
transitions in finite systems. This completely general analysis, which is
applicable to any physical system and extends towards the thermodynamic limit,
is based on the microcanonical entropy and its energetic derivative, the
inverse caloric temperature. Inflection points of this quantity signal
cooperative activity and thus serve as distinct indicators of transitions. We
demonstrate the power of this method through application to the long-standing
problem of liquid-solid transitions in elastic, flexible homopolymers.Comment: 4 pages, 3 figure
Modeling Reactive Wetting when Inertial Effects are Dominant
Recent experimental studies of molten metal droplets wetting high temperature
reactive substrates have established that the majority of triple-line motion
occurs when inertial effects are dominant. In light of these studies, this
paper investigates wetting and spreading on reactive substrates when inertial
effects are dominant using a thermodynamically derived, diffuse interface model
of a binary, three-phase material. The liquid-vapor transition is modeled using
a van der Waals diffuse interface approach, while the solid-fluid transition is
modeled using a phase field approach. The results from the simulations
demonstrate an O \left( t^{-\nicefrac{1}{2}} \right) spreading rate during
the inertial regime and oscillations in the triple-line position when the metal
droplet transitions from inertial to diffusive spreading. It is found that the
spreading extent is reduced by enhancing dissolution by manipulating the
initial liquid composition. The results from the model exhibit good qualitative
and quantitative agreement with a number of recent experimental studies of
high-temperature droplet spreading, particularly experiments of copper droplets
spreading on silicon substrates. Analysis of the numerical data from the model
suggests that the extent and rate of spreading is regulated by the spreading
coefficient calculated from a force balance based on a plausible definition of
the instantaneous interface energies. A number of contemporary publications
have discussed the likely dissipation mechanism in spreading droplets. Thus, we
examine the dissipation mechanism using the entropy-production field and
determine that dissipation primarily occurs in the locality of the triple-line
region during the inertial stage, but extends along the solid-liquid interface
region during the diffusive stage
Perturbation theory for plasmonic eigenvalues
We develop a perturbative approach for calculating, within the quasistatic
approximation, the shift of surface resonances in response to a deformation of
a dielectric volume. Our strategy is based on the conversion of the homogeneous
system for the potential which determines the plasmonic eigenvalues into an
inhomogeneous system for the potential's derivative with respect to the
deformation strength, and on the exploitation of the corresponding
compatibility condition. The resulting general expression for the first-order
shift is verified for two explicitly solvable cases, and for a realistic
example of a deformed nanosphere. It can be used for scanning the huge
parameter space of possible shape fluctuations with only quite small
computational effort
Time Dependent Floquet Theory and Absence of an Adiabatic Limit
Quantum systems subject to time periodic fields of finite amplitude, lambda,
have conventionally been handled either by low order perturbation theory, for
lambda not too large, or by exact diagonalization within a finite basis of N
states. An adiabatic limit, as lambda is switched on arbitrarily slowly, has
been assumed. But the validity of these procedures seems questionable in view
of the fact that, as N goes to infinity, the quasienergy spectrum becomes
dense, and numerical calculations show an increasing number of weakly avoided
crossings (related in perturbation theory to high order resonances). This paper
deals with the highly non-trivial behavior of the solutions in this limit. The
Floquet states, and the associated quasienergies, become highly irregular
functions of the amplitude, lambda. The mathematical radii of convergence of
perturbation theory in lambda approach zero. There is no adiabatic limit of the
wave functions when lambda is turned on arbitrarily slowly. However, the
quasienergy becomes independent of time in this limit. We introduce a
modification of the adiabatic theorem. We explain why, in spite of the
pervasive pathologies of the Floquet states in the limit N goes to infinity,
the conventional approaches are appropriate in almost all physically
interesting situations.Comment: 13 pages, Latex, plus 2 Postscript figure
Spin Dynamics of the LAGEOS Satellite in Support of a Measurement of the Earth's Gravitomagnetism
LAGEOS is an accurately-tracked, dense spherical satellite covered with 426
retroreflectors. The tracking accuracy is such as to yield a medium term (years
to decades) inertial reference frame determined via relatively inexpensive
observations. This frame is used as an adjunct to the more difficult and data
intensive VLBI absolute frame measurements. There is a substantial secular
precession of the satellite's line of nodes consistent with the classical,
Newtonian precession due to the non-sphericity of the earth. Ciufolini has
suggested the launch of an identical satellite (LAGEOS-3) into an orbit
supplementary to that of LAGEOS-1: LAGEOS-3 would then experience an equal and
opposite classical precession to that of LAGEOS-1. Besides providing a more
accurate real-time measurement of the earth's length of day and polar wobble,
this paired-satellite experiment would provide the first direct measurement of
the general relativistic frame-dragging effect. Of the five dominant error
sources in this experiment, the largest one involves surface forces on the
satellite, and their consequent impact on the orbital nodal precession. The
surface forces are a function of the spin dynamics of the satellite.
Consequently, we undertake here a theoretical effort to model the spin
ndynamics of LAGEOS. In this paper we present our preliminary results.Comment: 16 pages, RevTeX, LA-UR-94-1289. (Part I of II, postscript figures in
Part II
Quantum origin of the primordial fluctuation spectrum and its statistics
The usual account for the origin of cosmic structure during inflation is not
fully satisfactory, as it lacks a physical mechanism capable of generating the
inhomogeneity and anisotropy of our Universe, from an exactly homogeneous and
isotropic initial state associated with the early inflationary regime. The
proposal in [A. Perez, H. Sahlmann, and D. Sudarsky, Classical Quantum Gravity,
23, 2317, (2006)] considers the spontaneous dynamical collapse of the wave
function, as a possible answer to that problem. In this work, we review briefly
the difficulties facing the standard approach, as well as the answers provided
by the above proposal and explore their relevance to the investigations
concerning the characterization of the primordial spectrum and other
statistical aspects of the cosmic microwave background and large-scale matter
distribution. We will see that the new approach leads to novel ways of
considering some of the relevant questions, and, in particular, to distinct
characterizations of the non-Gaussianities that might have left imprints on the
available data.Comment: 27 pages. Revision to match the published versio
Singularity in the boundary resistance between superfluid He and a solid surface
We report new measurements in four cells of the thermal boundary resistance
between copper and He below but near the superfluid-transition
temperature . For fits of to the data yielded ,
whereas a fit to theoretical values based on the renormalization-group theory
yielded . Alternatively, a good fit of the theory to the data could
be obtained if the {\it amplitude} of the prediction was reduced by a factor
close to two. The results raise the question whether the boundary conditions
used in the theory should be modified.Comment: 4 pages, 4 figures, revte
Causal and localizable quantum operations
We examine constraints on quantum operations imposed by relativistic
causality. A bipartite superoperator is said to be localizable if it can be
implemented by two parties (Alice and Bob) who share entanglement but do not
communicate; it is causal if the superoperator does not convey information from
Alice to Bob or from Bob to Alice. We characterize the general structure of
causal complete measurement superoperators, and exhibit examples that are
causal but not localizable. We construct another class of causal bipartite
superoperators that are not localizable by invoking bounds on the strength of
correlations among the parts of a quantum system. A bipartite superoperator is
said to be semilocalizable if it can be implemented with one-way quantum
communication from Alice to Bob, and it is semicausal if it conveys no
information from Bob to Alice. We show that all semicausal complete measurement
superoperators are semilocalizable, and we establish a general criterion for
semicausality. In the multipartite case, we observe that a measurement
superoperator that projects onto the eigenspaces of a stabilizer code is
localizable.Comment: 23 pages, 7 figures, REVTeX, minor changes and references adde
Thermodynamic Theory of Weakly Excited Granular Materials
We present a thermodynamic theory of weakly excited two-dimensional granular
systems from the view point of elementary excitations of spinless Fermion
systems. We introduce a global temperature T that is associated with the
acceleration amplitude \Gamma in a vibrating bed. We show that the
configurational statistics of weakly excited granular materials in a vibrating
bed obey the Fermi statistics.Comment: 12 pages, 1 figure, To Appear in Phys. Rev. Lett. April, 199
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