4,159 research outputs found
Thermal derivation of the Coleman-De Luccia tunneling prescription
We derive the rate for transitions between de Sitter vacua by treating the
field theory on the static patch as a thermal system. This reproduces the
Coleman-De Luccia formalism for calculating the rate, but leads to a modified
interpretation of the bounce solution and a different prediction for the
evolution of the system after tunneling. The bounce is seen to correspond to a
sequence of configurations interpolating between initial and final
configurations on either side of the tunneling barrier, all of which are
restricted to the static patch. The final configuration, which gives the
initial data on the static patch for evolution after tunneling, is obtained
from one half of a slice through the center of the bounce, while the other half
gives the configuration before tunneling. The formalism makes no statement
about the fields beyond the horizon.
This approach resolves several puzzling aspects and interpretational issues
concerning the Coleman-De Luccia and Hawking-Moss bounces. We work in the limit
where the back reaction of matter on metric can be ignored, but argue that the
qualitative aspects remain in the more general case. The extension to tunneling
between anti-de Sitter vacua is discussed.Comment: 28 pages, 5 figures; minor rephrasing, typos correcte
Equivalence of Nonstatic Two-Pion-Exchange Nucleon-Nucleon Potentials
Off-shell aspects of the one-pion-exchange potential and their relationship
to different forms of the nonstatic (subleading-order) chiral two-pion-exchange
nucleon-nucleon potential are discussed. Various types of off-shell behavior
are categorized and numerous examples are given. Recently derived potentials
based on chiral approaches are supplemented by a rather general form of the
two-pion-exchange potential derived using old-fashioned methods. The latter is
closely related to a general form of one-pion-exchange relativistic corrections
and nonstatic two-pion-exchange three-nucleon forces developed long ago.Comment: 16 pages, latex -- Phys. Rev. C (to appear) -- Published versio
Observational Probes of Cosmic Acceleration
The accelerating expansion of the universe is the most surprising
cosmological discovery in many decades, implying that the universe is dominated
by some form of "dark energy" with exotic physical properties, or that
Einstein's theory of gravity breaks down on cosmological scales. The profound
implications of cosmic acceleration have inspired ambitious experimental
efforts to measure the history of expansion and growth of structure with
percent-level precision or higher. We review in detail the four most well
established methods for making such measurements: Type Ia supernovae, baryon
acoustic oscillations (BAO), weak gravitational lensing, and galaxy clusters.
We pay particular attention to the systematic uncertainties in these techniques
and to strategies for controlling them at the level needed to exploit "Stage
IV" dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We
briefly review a number of other approaches including redshift-space
distortions, the Alcock-Paczynski test, and direct measurements of H_0. We
present extensive forecasts for constraints on the dark energy equation of
state and parameterized deviations from GR, achievable with Stage III and Stage
IV experimental programs that incorporate supernovae, BAO, weak lensing, and
CMB data. We also show the level of precision required for other methods to
provide constraints competitive with those of these fiducial programs. We
emphasize the value of a balanced program that employs several of the most
powerful methods in combination, both to cross-check systematic uncertainties
and to take advantage of complementary information. Surveys to probe cosmic
acceleration produce data sets with broad applications, and they continue the
longstanding astronomical tradition of mapping the universe in ever greater
detail over ever larger scales.Comment: 289 pages, 55 figures. Accepted for publication in Physics Reports.
Description of changes since original version --- fractionally small but
significant in total --- is available at
http://www.astronomy.ohio-state.edu/~dhw/Revie
Non-Relativistic Spacetimes with Cosmological Constant
Recent data on supernovae favor high values of the cosmological constant.
Spacetimes with a cosmological constant have non-relativistic kinematics quite
different from Galilean kinematics. De Sitter spacetimes, vacuum solutions of
Einstein's equations with a cosmological constant, reduce in the
non-relativistic limit to Newton-Hooke spacetimes, which are non-metric
homogeneous spacetimes with non-vanishing curvature. The whole non-relativistic
kinematics would then be modified, with possible consequences to cosmology, and
in particular to the missing-mass problem.Comment: 15 pages, RevTeX, no figures, major changes in the presentation which
includes a new title and a whole new emphasis, version to appear in Clas.
Quant. Gra
Chiral Extrapolation, Renormalization, and the Viability of the Quark Model
The relationship of the quark model to the known chiral properties of QCD is
a longstanding problem in the interpretation of low energy QCD. In particular,
how can the pion be viewed as both a collective Goldstone boson quasiparticle
and as a valence quark antiquark bound state where universal hyperfine
interactions govern spin splittings in the same way as in the heavy quark
systems. We address this issue in a simplified model which; however, reproduces
all features of QCD relevant to this problem. A comparison of the many-body
solution to our model and the constituent quark model demonstrates that the
quark model is sufficiently flexible to describe meson hyperfine splitting
provided proper renormalization conditions and correct degrees of freedom are
employed consistently.Comment: 6 pages, 2 eps figures, uses revtex. Version to appear in Phys. Rev.
Let
Stability of the de Sitter spacetime in Horava-Lifshitz theory
The stability of de Sitter spacetime in Horava-Lifshitz theory of gravity
with projectability but without detailed balance condition is studied. It is
found that, in contrast to the case of the Minkowski background, the spin-0
graviton now is stable for any given , and free of ghost for
in the infrared limit, where is the dynamical coupling constant.Comment: Mod. Phys. Lett. A25, 2267-2279 (2010
Sloan Digital Sky Survey III Photometric Quasar Clustering: Probing the Initial Conditions of the Universe using the Largest Volume
The Sloan Digital Sky Survey has surveyed 14,555 square degrees of the sky,
and delivered over a trillion pixels of imaging data. We present the
large-scale clustering of 1.6 million quasars between z = 0.5 and z = 2.5 that
have been classified from this imaging, representing the highest density of
quasars ever studied for clustering measurements. This data set spans ~11,000
square degrees and probes a volume of 80(Gpc/h)^3. In principle, such a large
volume and medium density of tracers should facilitate high-precision
cosmological constraints. We measure the angular clustering of photometrically
classified quasars using an optimal quadratic estimator in four redshift slices
with an accuracy of ~25% over a bin width of l ~10 - 15 on scales corresponding
to matter-radiation equality and larger (l ~ 2 - 30). Observational systematics
can strongly bias clustering measurements on large scales, which can mimic
cosmologically relevant signals such as deviations from Gaussianity in the
spectrum of primordial perturbations. We account for systematics by employing a
new method recently proposed by Agarwal et al. (2014) to the clustering of
photometrically classified quasars. We carefully apply our methodology to
mitigate known observational systematics and further remove angular bins that
are contaminated by unknown systematics. Combining quasar data with the
photometric luminous red galaxy (LRG) sample of Ross et al. (2011) and Ho et
al. (2012), and marginalizing over all bias and shot noise-like parameters, we
obtain a constraint on local primordial non-Gaussianity of fNL = -113+/-154
(1\sigma error). [Abridged]Comment: 35 pages, 15 figure
The clustering of intermediate redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey
We measure the quasar two-point correlation function over the redshift range
2.2<z<2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a
homogeneous subset of the data consisting of 27,129 quasars with spectroscopic
redshifts---by far the largest such sample used for clustering measurements at
these redshifts to date. The sample covers 3,600 square degrees, corresponding
to a comoving volume of 9.7(Gpc/h)^3 assuming a fiducial LambdaCDM cosmology,
and it has a median absolute i-band magnitude of -26, k-corrected to z=2. After
accounting for redshift errors we find that the redshift space correlation
function is fit well by a power-law of slope -2 and amplitude s_0=(9.7\pm
0.5)Mpc/h over the range 3<s<25Mpc/h. The projected correlation function, which
integrates out the effects of peculiar velocities and redshift errors, is fit
well by a power-law of slope -1 and r_0=(8.4\pm 0.6)Mpc/h over the range
4<R<16Mpc/h. There is no evidence for strong luminosity or redshift dependence
to the clustering amplitude, in part because of the limited dynamic range in
our sample. Our results are consistent with, but more precise than, previous
measurements at similar redshifts. Our measurement of the quasar clustering
amplitude implies a bias factor of b~3.5 for our quasar sample. We compare the
data to models to constrain the manner in which quasars occupy dark matter
halos at z~2.4 and infer that such quasars inhabit halos with a characteristic
mass of ~10^{12}Msun/h with a duty cycle for the quasar activity of 1 per
cent.Comment: 20 pages, 18 figures. Minor modifications to match version accepted
by journa
Nucleon-Nucleon Effective Field Theory Without Pions
Nuclear processes involving momenta much below the mass of the pion may be
described by an effective field theory in which the pions do not appear as
explicit degrees of freedom. The effects of the pion and all other virtual
hadrons are reproduced by the coefficients of gauge-invariant local operators
involving the nucleon field. Nucleon-nucleon scattering phase shift data
constrains many of the coefficients that appear in the effective Lagrangean but
at some order in the expansion coefficients enter that must be constrained by
other observables. We compute several observables in the two-nucleon sector up
to next-to-next-to leading order in the effective field theory without pions,
or to the order at which a counterterm involving four-nucleon field operators
is encountered. Effective range theory is recovered from the effective field
theory up to the order where relativistic corrections enter or where
four-nucleon-external current local operators arise. For the deuteron magnetic
moment, quadrupole moment and the radiative capture cross
section a four-nucleon-one-photon counterterm exists at next-to-leading order.
The electric polarizability and electric charge form factor of the deuteron are
determined up to next-to-next-to-leading order, which includes the first
appearance of relativistic corrections.Comment: 27 pages, 8 figures, latex. SD-mixing, quadrupole moment modifie
Role of heavy-meson exchange in pion production near threshold
Recent calculations of -wave pion production have severely underestimated
the accurately known \ total cross section near
threshold. In these calculations, only the single-nucleon axial-charge operator
is considered. We have calculated, in addition to the one-body term, the
two-body contributions to this reaction that arise from the exchange of mesons.
We find that the inclusion of the scalar -meson exchange current (and
lesser contributions from other mesons) increases the cross section by about a
factor of five, and leads to excellent agreement with the data. The results are
neither very sensitive to changes in the distorting potential that generates
the wave function, nor to different choices for the meson-nucleon form
factors. We argue that \ data provide direct
experimental evidence for meson-exchange contributions to the axial current.Comment: 28 Pages, IU-NTC #93-0
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