10,925 research outputs found
Pair Creation of Dilaton Black Holes in Extended Inflation
Dilatonic Charged Nariai instantons mediate the nucleation of black hole
pairs during extended chaotic inflation. Depending on the dilaton and inflaton
fields, the black holes are described by one of two approximations in the
Lorentzian regime. For each case we find Euclidean solutions that satisfy the
no boundary proposal. The complex initial values of the dilaton and inflaton
are determined, and the pair creation rate is calculated from the Euclidean
action. Similar to standard inflation, black holes are abundantly produced near
the Planck boundary, but highly suppressed later on. An unusual feature we find
is that the earlier in inflation that the dilatonic black holes are created,
the more highly charged they can be.Comment: 23 pages, LaTeX, 6 figures; submitted to Phys. Rev.
Brane Inflation from Rotation of D4 Brane
In this paper, a inflationary model from the rotation of D4-brane is
constructed. We show that for a very wide rage of parameter, this model
satisfies the observation and find that regarded as inflaton, the rotation of
branes may be more nature than the distance between branes. Our model offers a
new avenue for brane inflation.Comment: 6 pages, no figure
Bounds on isocurvature perturbations from CMB and LSS data
We obtain very stringent bounds on the possible cold dark matter, baryon and
neutrino isocurvature contributions to the primordial fluctuations in the
Universe, using recent cosmic microwave background and large scale structure
data. In particular, we include the measured temperature and polarization power
spectra from WMAP and ACBAR, as well as the matter power spectrum from the 2dF
galaxy redshift survey. Neglecting the possible effects of spatial curvature,
tensor perturbations and reionization, we perform a Bayesian likelihood
analysis with nine free parameters, and find that the amplitude of the
isocurvature component cannot be larger than about 31% for the cold dark matter
mode, 91% for the baryon mode, 76% for the neutrino density mode, and 60% for
the neutrino velocity mode, at 2-sigma, for uncorrelated models. On the other
hand, for correlated adiabatic and isocurvature components, the fraction could
be slightly larger. However, the cross-correlation coefficient is strongly
constrained, and maximally correlated/anticorrelated models are disfavored.
This puts strong bounds on the curvaton model, independently of the bounds on
non-Gaussianity.Comment: 4 pages, 1 figure, some minor corrections; version accepted in PR
General Relativity as an Attractor in Scalar-Tensor Stochastic Inflation
Quantum fluctuations of scalar fields during inflation could determine the
very large-scale structure of the universe. In the case of general
scalar-tensor gravity theories these fluctuations lead to the diffusion of
fundamental constants like the Planck mass and the effective Brans--Dicke
parameter, . In the particular case of Brans--Dicke gravity, where
is constant, this leads to runaway solutions with infinitely large
values of the Planck mass. However, in a theory with variable we find
stationary probability distributions with a finite value of the Planck mass
peaked at exponentially large values of after inflation. We conclude
that general relativity is an attractor during the quantum diffusion of the
fields.Comment: LaTeX (with RevTex) 11 pages, 2 uuencoded figures appended, also
available on WWW via http://star.maps.susx.ac.uk/index.htm
Effective CP violation in the Standard Model
We study the strength of effective CP violation originating from the CKM
matrix in the effective action obtained by integrating out the fermions in the
Standard Model. Using results obtained by Salcedo for the effective action in a
general chiral gauge model, we find that there are no CKM CP-violating terms to
fourth order in a gauge-covariant derivative expansion that is non-perturbative
in the Higgs field. The details of the calculation suggest that, at zero
temperature, the strength of CP violation is approximately independent of the
overall scale of the Yukawa couplings. Thus, order of magnitude estimates based
on Jarlskog's invariant could be too small by a factor of about 10^{17}.Comment: 19 pages, no figure
Enlarging instruction streams
The stream fetch engine is a high-performance fetch architecture based on the concept of an instruction stream. We call a sequence of instructions from the target of a taken branch to the next taken branch, potentially containing multiple basic blocks, a stream. The long length of instruction streams makes it possible for the stream fetch engine to provide a high fetch bandwidth and to hide the branch predictor access latency, leading to performance results close to a trace cache at a lower implementation cost and complexity. Therefore, enlarging instruction streams is an excellent way to improve the stream fetch engine. In this paper, we present several hardware and software mechanisms focused on enlarging those streams that finalize at particular branch types. However, our results point out that focusing on particular branch types is not a good strategy due to Amdahl's law. Consequently, we propose the multiple-stream predictor, a novel mechanism that deals with all branch types by combining single streams into long virtual streams. This proposal tolerates the prediction table access latency without requiring the complexity caused by additional hardware mechanisms like prediction overriding. Moreover, it provides high-performance results which are comparable to state-of-the-art fetch architectures but with a simpler design that consumes less energy.Peer ReviewedPostprint (published version
Measuring the transition to homogeneity with photometric redshift surveys
We study the possibility of detecting the transition to homogeneity using
photometric redshift catalogs. Our method is based on measuring the fractality
of the projected galaxy distribution, using angular distances, and relies only
on observable quantites. It thus provides a way to test the Cosmological
Principle in a model-independent unbiased way. We have tested our method on
different synthetic inhomogeneous catalogs, and shown that it is capable of
discriminating some fractal models with relatively large fractal dimensions, in
spite of the loss of information due to the radial projection. We have also
studied the influence of the redshift bin width, photometric redshift errors,
bias, non-linear clustering, and surveyed area, on the angular homogeneity
index H2 ({\theta}) in a {\Lambda}CDM cosmology. The level to which an upcoming
galaxy survey will be able to constrain the transition to homogeneity will
depend mainly on the total surveyed area and the compactness of the surveyed
region. In particular, a Dark Energy Survey (DES)-like survey should be able to
easily discriminate certain fractal models with fractal dimensions as large as
D2 = 2.95. We believe that this method will have relevant applications for
upcoming large photometric redshift surveys, such as DES or the Large Synoptic
Survey Telescope (LSST).Comment: 14 pages, 14 figure
Metric perturbations in two-field inflation
We study the metric perturbations produced during inflation in models with
two scalar fields evolving simultaneously. In particular, we emphasize how the
large-scale curvature perturbation on fixed energy density
hypersurfaces may not be conserved in general for multiple field inflation due
to the presence of entropy as well as adiabatic fluctuations. We show that the
usual method of solving the linearized perturbation equations is equivalent to
the recently proposed analysis of Sasaki and Stewart in terms of the perturbed
expansion along neighboring trajectories in field-space. In the case of a
separable potential it is possible to compute in the slow-roll approximation
the spectrum of density perturbations and gravitational waves at the end of
inflation. In general there is an inequality between the ratio of tensor to
scalar perturbations and the tilt of the gravitational wave spectrum, which
becomes an equality when only adiabatic perturbations are possible and
is conserved.Comment: RevTex, 9 pages, 1 uuencoded figure appended, also available on WWW
via http://star.maps.susx.ac.uk/index.htm
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