19,995 research outputs found
The cosmological constant as an eigenvalue of the Hamiltonian constraint in Horava-Lifshits theory
In the framework of Horava-Lifshitz theory, we study the eigenvalues
associated with the Wheeler-DeWitt equation representing the vacuum expectation
values associated with the cosmological constant. The explicit calculation is
performed with the help of a variational procedure with trial wave functionals
of the Gaussian type. We analyze both the case with the detailed balanced
condition and the case without it. In the case without the detailed balance, we
find the existence of an eigenvalue depending on the set of coupling constants
(g2,g3) and (g4,g5,g6), respectively, and on the physical scale.Comment: RevTeX,11 Pages, Substantial Improvements. References added. To
appear in Phys.Rev.
Mapping dynamical heterogeneity in structural glasses to correlated fluctuations of the time variables
Dynamical heterogeneities -- strong fluctuations near the glass transition --
are believed to be crucial to explain much of the glass transition
phenomenology. One possible hypothesis for their origin is that they emerge
from soft (Goldstone) modes associated with a broken continuous symmetry under
time reparametrizations. To test this hypothesis, we use numerical simulation
data from four glass-forming models to construct coarse grained observables
that probe the dynamical heterogeneity, and decompose the fluctuations of these
observables into two transverse components associated with the postulated
time-fluctuation soft modes and a longitudinal component unrelated to them. We
find that as temperature is lowered and timescales are increased, the time
reparametrization fluctuations become increasingly dominant, and that their
correlation volumes grow together with the correlation volumes of the dynamical
heterogeneities, while the correlation volumes for longitudinal fluctuations
remain small.Comment: v4: Detailed analysis of transverse and longitudinal parts. One
figure removed, two added. v3: Explicit decomposition into transverse and
longitudinal parts, discussion of correlation volumes. One more figure v2:
Modified introduction and forma
Luminescence Dating of Beach Dunes and Fluvial Sediments, Nayarit, Mexico
The Pacific coast of the state of Nayarit, Mexico, is dominated by extensive sand dune systems and lagoons. 16 samples from three transects through dunes near the town of Santa Cruz were collected to establish ages of the beach dune ridges and establish a robust chronology, to assist in understanding the depositional rates associated with different phases of the evolution of the strand plain. In addition, three samples were collected from a fluvial terrace on the San Pedro River which enters the Pacific near the southernmost of the dune transects. Quartz grains were extracted from the samples, and analysed using an Optically Stimulated Luminescence (OSL) method to determine stored dose and ages.
The samples collected nearest the current coast have produced dates of 1500-1900AD, with samples further from the coast being progressively older, spanning a period of over 2000 years with oldest measured date of 400BC. The dates for the upper samples from the San Pedro River is consistent with the ages of the dunes nearest the coast, with the lower sample date closer to the dates of the older dunes further from the coast, indicating that this fluvial deposit was laid down over the same time period as the dune formation
Time reparametrization invariance in arbitrary range p-spin models: symmetric versus non-symmetric dynamics
We explore the existence of time reparametrization symmetry in p-spin models.
Using the Martin-Siggia-Rose generating functional, we analytically probe the
long-time dynamics. We perform a renormalization group analysis where we
systematically integrate over short timescale fluctuations. We find three
families of stable fixed points and study the symmetry of those fixed points
with respect to time reparametrizations. One of those families is composed
entirely of symmetric fixed points, which are associated with the low
temperature dynamics. The other two families are composed entirely of
non-symmetric fixed points. One of these two non-symmetric families corresponds
to the high temperature dynamics.
Time reparametrization symmetry is a continuous symmetry that is
spontaneously broken in the glass state and we argue that this gives rise to
the presence of Goldstone modes. We expect the Goldstone modes to determine the
properties of fluctuations in the glass state, in particular predicting the
presence of dynamical heterogeneity.Comment: v2: Extensively modified to discuss both high temperature
(non-symmetric) and low temperature (symmetric) renormalization group fixed
points. Now 16 pages with 1 figure. v1: 13 page
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