2,570 research outputs found
Cosmology in the Randall-Sundrum Brane World Scenario
The cosmology of the Randall-Sundrum scenario for a positive tension brane in
a 5-D Universe with localized gravity has been studied extensively recently.
Here we extend it to more general situations. We consider the time-dependent
situation where the two sides of the brane are different AdS/Schwarzschild
spaces. We show that the expansion rate in these models during inflation could
be larger than in brane worlds with compactified extra dimensions of fixed
size. The enhanced expansion rate could lead to the production of density
perturbations of substantially larger amplitude.Comment: 11 pages, revte
Exciting gauge field and gravitons in a brane-anti-brane annihilation
In this paper we point out the inevitability of an explosive production of
gauge field and gravity wave during an open string tachyon condensation in a
cosmological setting. We will be particularly studying an example of
brane-anti-brane inflation in a warped throat where inflation ends via tachyon
condensation. We point out that a tachyonic instability helps fragmenting the
homogeneous tachyon and excites gauge field and contributes to the stress
energy tensor which also feeds into the gravity waves.Comment: 4 pages 8 fig
Double-beta decay matrix elements for
Double-beta decay matrix elements (ME) for are calculated with different quasi random phase approximation (QRPA)-based methods. First, the ME for the two-neutrino mode are computed using two choices for the single particle (s.p.) basis: i) full shells and ii) full shells. When calculated with the renormalized QRPA (RQRPA) and full-RQRPA their values are rather dependent on the size of the single particle basis used, while calculated with proton-neutron QRPA (pnQRPA) and second-QRPA approaches such a dependence was found to be small. The Ikeda sum rule was well fulfilled within pnQRPA for both choices of the s.p. basis and with a good approximation within second-QRPA, while the RQRPA and full-RQRPA methods give deviations up to 21%. Further, the ME for the neutrinoless mode are calculated with the pnQRPA, RQRPA and full-RQRPA methods. They all give close results for the calculation with the smaller basis (i), while for the larger basis (ii), the results differ significantly either from one method to another or within the same method. Finally, using the most recent experimental limit for the decay half-life of a critical discussion on the upper limits for the neutrino mass parameter obtained with different theoretical approaches is given
Shell-model calculations of two-neutrino double-beta decay rates of Ca with GXPF1A interaction
The two-neutrino double beta decay matrix elements and half-lives of
Ca, are calculated within a shell-model approach for transitions to the
ground state and to the first excited state of Ti. We use the full
model space and the GXPF1A interaction, which was recently proposed to
describe the spectroscopic properties of the nuclei in the nuclear mass region
A=47-66. Our results are =
and = . The result for the
decay to the Ti 0 ground state is in good agreement with experiment.
The half-life for the decay to the 2 state is two orders of magnitude
larger than obtained previously.Comment: 6 pages, 4 figure
Qubits as spectrometers of dephasing noise
We present a procedure for direct characterization of the dephasing noise
acting on a single qubit by making repeated measurements of the qubit coherence
under suitably chosen sequences of controls. We show that this allows a
numerical reconstruction of the short time noise correlation function and that
it can be combined with a series of measurements under free evolution to allow
a characterization of the noise correlation function over many orders of
magnitude range in timescale. We also make an analysis of the robustness and
reliability of the estimated correlation functions. Application to a simple
model of two uncorrelated noise fluctuators using decoupling pulse sequences
shows that the approach provides a useful route for experimental
characterization of dephasing noise and its statistical properties in a variety
of condensed phase and atomic systems.Comment: 10 pages, 3 figure
A Probabilistic Analysis of Kademlia Networks
Kademlia is currently the most widely used searching algorithm in P2P
(peer-to-peer) networks. This work studies an essential question about Kademlia
from a mathematical perspective: how long does it take to locate a node in the
network? To answer it, we introduce a random graph K and study how many steps
are needed to locate a given vertex in K using Kademlia's algorithm, which we
call the routing time. Two slightly different versions of K are studied. In the
first one, vertices of K are labelled with fixed IDs. In the second one,
vertices are assumed to have randomly selected IDs. In both cases, we show that
the routing time is about c*log(n), where n is the number of nodes in the
network and c is an explicitly described constant.Comment: ISAAC 201
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