1,426 research outputs found
EPIC 219217635: A Doubly Eclipsing Quadruple System Containing an Evolved Binary
We have discovered a doubly eclipsing, bound, quadruple star system in the
field of K2 Campaign 7. EPIC 219217635 is a stellar image with that
contains an eclipsing binary (`EB') with d and a second EB with
d. We have obtained followup radial-velocity (`RV')
spectroscopy observations, adaptive optics imaging, as well as ground-based
photometric observations. From our analysis of all the observations, we derive
good estimates for a number of the system parameters. We conclude that (1) both
binaries are bound in a quadruple star system; (2) a linear trend to the RV
curve of binary A is found over a 2-year interval, corresponding to an
acceleration, cm s; (3) small
irregular variations are seen in the eclipse-timing variations (`ETVs')
detected over the same interval; (4) the orbital separation of the quadruple
system is probably in the range of 8-25 AU; and (5) the orbital planes of the
two binaries must be inclined with respect to each other by at least
25. In addition, we find that binary B is evolved, and the cooler and
currently less massive star has transferred much of its envelope to the
currently more massive star. We have also demonstrated that the system is
sufficiently bright that the eclipses can be followed using small ground-based
telescopes, and that this system may be profitably studied over the next decade
when the outer orbit of the quadruple is expected to manifest itself in the ETV
and/or RV curves.Comment: Accepted for publication in MNRA
An Attempt to Determine the Largest Scale of Primordial Density Perturbations in the Universe
Inflationary cosmology predicts that the particle horizon should be
generically much bigger than the present-day Hubble radius, . This
implies a special regime of super-Hubble scale energy density fluctuations
imprinted on the cosmic microwave background radiation (CMBR), which from
present theory could only be explained by inflation Causality constraints are
used to determine models for the power spectrum that accommodate a suppression
scale. A three parameter likelihood analysis is performed of the COBE-DMR
4-year data with respect to the amplitude, spectral index, and suppression
scale. It is found that all suppression length scales larger than are
consistent with the data, but that scales of order are slightly
preferred, at roughly the one-sigma level. Many non-inflation models would be
consistent with a small suppression length scale, whereas for standard
inflation models, the duration of the inflation epoch would have to be bounded
by a fairly small upper limit. Suppression scales smaller than are
strongly excluded by the anisotrophy data.Comment: 9 pages, Latex, 1 figure, additional tests reporte
Holographic Description of AdS Cosmologies
To gain insight in the quantum nature of the big bang, we study the dual
field theory description of asymptotically anti-de Sitter solutions of
supergravity that have cosmological singularities. The dual theories do not
appear to have a stable ground state. One regularization of the theory causes
the cosmological singularities in the bulk to turn into giant black holes with
scalar hair. We interpret these hairy black holes in the dual field theory and
use them to compute a finite temperature effective potential. In our study of
the field theory evolution, we find no evidence for a "bounce" from a big
crunch to a big bang. Instead, it appears that the big bang is a rare
fluctuation from a generic equilibrium quantum gravity state.Comment: 34 pages, 8 figures, v2: minor changes, references adde
Rolling Tachyon in Brane World Cosmology from Superstring Field Theory
The pressureless tachyonic matter recently found in superstring field theory
has an over-abundance problem in cosmology. We argue that this problem is
naturally solved in the brane inflationary scenario if almost all of the
tachyon energy is drained (via its coupling to the inflaton and matter fields)
to heating the universe, while the rest of the tachyon energy goes to a network
of cosmic strings (lower-dimensional BPS D-branes) produced during the tachyon
rolling at the end of inflation.Comment: 4 pages, one figure. This version quantifies constraints on various
phenomenological models for tachyon deca
The status of GEO 600
The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
Tachyonic Instability and Dynamics of Spontaneous Symmetry Breaking
Spontaneous symmetry breaking usually occurs due to the tachyonic (spinodal)
instability of a scalar field near the top of its effective potential at . Naively, one might expect the field to fall from the top of the
effective potential and then experience a long stage of oscillations with
amplitude O(v) near the minimum of the effective potential at until
it gives its energy to particles produced during these oscillations. However,
it was recently found that the tachyonic instability rapidly converts most of
the potential energy V(0) into the energy of colliding classical waves of the
scalar field. This conversion, which was called "tachyonic preheating," is so
efficient that symmetry breaking typically completes within a single
oscillation of the field distribution as it rolls towards the minimum of its
effective potential. In this paper we give a detailed description of tachyonic
preheating and show that the dynamics of this process crucially depend on the
shape of the effective potential near its maximum. In the simplest models where
near the maximum, the process occurs solely due to
the tachyonic instability, whereas in the theories with n > 2
one encounters a combination of the effects of tunneling, tachyonic instability
and bubble wall collisions.Comment: 40 pages, 14 figures, revte
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
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