38,284 research outputs found
Minimal Theoretical Uncertainties in Inflationary Predictions
During inflation, primordial energy density fluctuations are created from
approximate de Sitter vacuum quantum fluctuations redshifted out of the horizon
after which they are frozen as perturbations in the background curvature. In
this paper we demonstrate that there exists an intrinsic theoretical
uncertainty in the inflationary predictions for the curvature perturbations due
to the failure of the well known prescriptions to specify the vacuum uniquely.
Specifically, we show that the two often used prescriptions for defining the
initial vacuum state -- the Bunch-Davies prescription and the adiabatic vacuum
prescription (even if the adiabaticity order to which the vacuum is specified
is infinity) -- fail to specify the vacuum uniquely in generic inflationary
spacetimes in which the total duration of inflation is finite. This conclusion
holds despite the absence of any trans-Planckian effects or effective field
theory cutoff related effects. We quantify the uncertainty which is applicable
to slow roll inflationary scenarios as well as for general FRW spacetimes and
find that the uncertainty is generically small. This uncertainty should be
treated as a minimal uncertainty that underlies all curvature perturbation
calculations.Comment: LaTeX file, 35 pages; some typos correcte
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
Inverse Avalanches On Abelian Sandpiles
A simple and computationally efficient way of finding inverse avalanches for
Abelian sandpiles, called the inverse particle addition operator, is presented.
In addition, the method is shown to be optimal in the sense that it requires
the minimum amount of computation among methods of the same kind. The method is
also conceptually nice because avalanche and inverse avalanche are placed in
the same footing.Comment: 5 pages with no figure IASSNS-HEP-94/7
Non-monotonic temperature dependent transport in graphene grown by Chemical Vapor Deposition
Temperature-dependent resistivity of graphene grown by chemical vapor
deposition (CVD) is investigated. We observe in low mobility CVD graphene
device a strong insulating behavior at low temperatures and a metallic behavior
at high temperatures manifesting a non-monotonic in the temperature dependent
resistivity.This feature is strongly affected by carrier density modulation. To
understand this anomalous temperature dependence, we introduce thermal
activation of charge carriers in electron-hole puddles induced by randomly
distributed charged impurities. Observed temperature evolution of resistivity
is then understood from the competition among thermal activation of charge
carriers, temperature-dependent screening and phonon scattering effects. Our
results imply that the transport property of transferred CVD-grown graphene is
strongly influenced by the details of the environmentComment: 7 pages, 3 figure
On the gravitational production of superheavy dark matter
The dark matter in the universe can be in the form of a superheavy matter
species (WIMPZILLA). Several mechanisms have been proposed for the production
of WIMPZILLA particles during or immediately following the inflationary epoch.
Perhaps the most attractive mechanism is through gravitational particle
production, where particles are produced simply as a result of the expansion of
the universe. In this paper we present a detailed numerical calculation of
WIMPZILLA gravitational production in hybrid-inflation models and
natural-inflation models. Generalizing these findings, we also explore the
dependence of the gravitational production mechanism on various models of
inflation. We show that superheavy dark matter production seems to be robust,
with Omega_X h^2 ~ (M_X / (10^11 GeV))^2 (T_RH / (10^9 GeV)), so long as M_X <
H_I, where M_X is the WIMPZILLA mass, T_RH is the reheat temperature, and H_I
is the expansion rate of the universe during inflation.Comment: 26 pages, 7 figures; LaTeX; submitted to Physical Review D; minor
typographical error correcte
VIVA, VLA Imaging of Virgo spirals in Atomic gas: I. The Atlas & The HI Properties
We present the result of a new VLA HI Imaging survey of Virgo galaxies, VIVA
(the VLA Imaging survey of Virgo galaxies in Atomic gas). The survey includes
high resolution HI data of 53 carefully selected late type galaxies (48 spirals
and 5 irregular systems). The goal is to study environmental effects on HI gas
properties of cluster galaxies to understand which physical mechanisms affect
galaxy evolution in different density regions, and to establish how far out the
impact of the cluster reaches. As a dynamically young cluster, Virgo contains
examples of galaxies experiencing a variety of environmental effects. Its
nearness allows us to study each galaxy in great detail. We have selected Virgo
galaxies with a range of star formation properties in low to high density
regions (at the projected distance from M87, d_87=0.3-3.3 Mpc). Contrary to pr
evious studies, more than half of the galaxies in the sample (~60%) are fainter
than 12 mag in B_T. Overall, the selected galaxies represent the late type
Virgo galaxies (S0/a to Sd/Irr) down to m_p<~14.6 fairly well in morphological
type, systemic velocity, subcluster membership, HI mass and deficiency. In this
paper (VIVA I: the atlas and the HI properties), we present HI maps and
properties, and describe the HI morphology and kinematics of individual
galaxies in detail (abbreviated).Comment: K band magnitudes for 6 galaxies in Table 3 have been corrected. One
of the labels in Figure 8 is corrected and an omission in the acknowledgments
has been added. The latter two were correct in the previous astro-ph version
but are wrong in the journal version. A full resolution with the complete HI
atlas can be downloaded at http://www.astro.yale.edu/viva/pub.htm
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