1,336,815 research outputs found
Dirac operator normality and chiral properties
Normality and \ga-hermiticity are what gives rise to chiral properties and
rules. The Ginsparg-Wilson (GW) relation is only one of the possible spectral
constraints. The sum rule for chiral differences of real modes has important
consequences. The alternative transformation of L\"uscher gives the same Ward
identity as the usual chiral one (if zero modes are properly treated). Imposing
normality on a general function of the hermitean Wilson-Dirac operator
leads at the same time to the GW relation and to the Neuberger operator.Comment: LATTICE99(chiral fermions), 3 page
The Evolution of the M-sigma Relation
(Abridged) We examine the evolution of the black hole mass - stellar velocity
dispersion (M-sigma) relation over cosmic time using simulations of galaxy
mergers that include feedback from supermassive black hole growth. We consider
mergers of galaxies varying the properties of the progenitors to match those
expected at redshifts z=0-6. We find that the slope of the resulting M-sigma
relation is the same at all redshifts considered. For the same feedback
efficiency that reproduces the observed amplitude of the M-sigma relation at
z=0, there is a weak redshift-dependence to the normalization that results from
an increasing velocity dispersion for a given galactic stellar mass. We develop
a formalism to connect redshift evolution in the M-sigma relation to the
scatter in the local relation at z=0. We show that the scatter in the local
relation places severe constraints on the redshift evolution of both the
normalization and slope of the M-sigma relation. Furthermore, we demonstrate
that cosmic downsizing introduces a black hole mass-dependent dispersion in the
M-sigma relation and that the skewness of the distribution about the locally
observed M-sigma relation is sensitive to redshift evolution in the
normalization and slope. In principle, these various diagnostics provide a
method for differentiating between theories for producing the M-sigma relation.
In agreement with existing constraints, our simulations imply that hierarchical
structure formation should produce the relation with small intrinsic scatter.Comment: 12 pages, 6 figures, version accepted by Ap
Gamma-Ray Burst Jet Profiles And Their Signatures
HETE-II and BeppoSAX have produced a sample of GRBs and XRFs with known
redshifts and . This sample provides four important empirical
constraints on the nature of the source jets: Log is approximately
uniformly distributed over several orders of magnitude; the inferred prompt
energy Log is narrowly distributed; the Amati relation holds
between and ; and the Ghirlanda relation holds between
and .
We explore the implications of these constraints for GRB jet structure during
the prompt emission phase. We infer the underlying angular profiles from the
first two of the above constraints assuming all jets have the same profile and
total energy, and show that such ``universal jet'' models cannot satisfy both
constraints.
We introduce a general and efficient method for calculating relativistic
emission distributions and distributions from jets with arbitrary
(smooth) angular jet profiles. We also exhibit explicit analytical formulas for
emission from top-hat jets (which are not smooth). We use these methods to
exhibit and as a function of viewing angle, for several
interesting families of GRB jet profiles. We use the same methods to calculate
expected frequency distributions of and for the same
families of models.
We then proceed to explore the behavior of universal jet models under a range
of profile shapes and parameters, to map the extent to which these models can
conform to the above four empirical constraints.Comment: 71 page, 33 figures. Submitted to Ap
The XMM Cluster Survey: Forecasting cosmological and cluster scaling-relation parameter constraints
We forecast the constraints on the values of sigma_8, Omega_m, and cluster
scaling relation parameters which we expect to obtain from the XMM Cluster
Survey (XCS). We assume a flat Lambda-CDM Universe and perform a Monte Carlo
Markov Chain analysis of the evolution of the number density of galaxy clusters
that takes into account a detailed simulated selection function. Comparing our
current observed number of clusters shows good agreement with predictions. We
determine the expected degradation of the constraints as a result of
self-calibrating the luminosity-temperature relation (with scatter), including
temperature measurement errors, and relying on photometric methods for the
estimation of galaxy cluster redshifts. We examine the effects of systematic
errors in scaling relation and measurement error assumptions. Using only (T,z)
self-calibration, we expect to measure Omega_m to +-0.03 (and Omega_Lambda to
the same accuracy assuming flatness), and sigma_8 to +-0.05, also constraining
the normalization and slope of the luminosity-temperature relation to +-6 and
+-13 per cent (at 1sigma) respectively in the process. Self-calibration fails
to jointly constrain the scatter and redshift evolution of the
luminosity-temperature relation significantly. Additional archival and/or
follow-up data will improve on this. We do not expect measurement errors or
imperfect knowledge of their distribution to degrade constraints significantly.
Scaling-relation systematics can easily lead to cosmological constraints 2sigma
or more away from the fiducial model. Our treatment is the first exact
treatment to this level of detail, and introduces a new `smoothed ML' estimate
of expected constraints.Comment: 28 pages, 17 figures. Revised version, as accepted for publication in
MNRAS. High-resolution figures available at http://xcs-home.org (under
"Publications"
Incentive compatibility and pricing under moral hazard
We study a simple insurance economy with moral hazard, in which random contracts overcome the non-convexities generated by the incentive-compatibility constraints. The novelty is that we use linear programming and duality theory to study the relation between incentive compatibility and pricing. Using linear programming has the advantage that we can impose the incentive-compatibility constraints on the agents that are uninformed (the insurance firms). In contrast, most of the general equilibrium literature imposes them on the informed agents (the consumers). We derive the two welfare theorems, establish the existence of a competitive equilibrium, and characterize the equilibrium prices and allocations. Our competitive equilibrium has two key properties: (i) the equilibrium prices reflect all the relevant information, including the welfare costs arising from the incentive-compatibility constraints; (ii) the equilibrium allocations are the same as when the incentive-compatibility constraints are imposed on the consumers
The - relation for type Ia supernovae, locally inhomogeneous cosmological models, and the nature of dark matter
The - relation for type Ia supernovae is one of the key pieces of
evidence supporting the cosmological `concordance model' with and . However, it is well known that the
- relation depends not only on and (with as
a scale factor) but also on the density of matter along the line of sight,
which is not necessarily the same as the large-scale density. I investigate to
what extent the measurement of and depends on this
density when it is characterized by the parameter (),
which describes the ratio of density along the line of sight to the overall
density. I also discuss what constraints can be placed on , both with and
without constraints on and in addition to those from the
- relation for type~Ia supernovae.Comment: 11 pages, 17 figures, published in Monthly Notices of the Royal
Astronomical Society. This version contains minor changes made while
correcting proofs in order to correspond as closely as practical to the
offical version. No changes in content. Related information available at
http://www.astro.multivax.de:8000/helbig/research/publications/info/etasnia.htm
Solving Virasoro Constraints on Integrable Hierarchies via the Kontsevich-Miwa Transform
We solve Virasoro constraints on the KP hierarchy in terms of minimal
conformal models. The constraints we start with are implemented by the Virasoro
generators depending on a background charge . Then the solutions to the
constraints are given by the theory which has the same field content as the
David-Distler-Kawai theory: it consists of a minimal matter scalar with
background charge , dressed with an extra `Liouville' scalar. The
construction is based on a generalization of the Kontsevich parametrization of
the KP times achieved by introducing into it Miwa parameters which depend on
the value of . Under the thus defined Kontsevich-Miwa transformation, the
Virasoro constraints are proven to be equivalent to a master equation depending
on the parameter . The master equation is further identified with a
null-vector decoupling equation. We conjecture that constraints on
the KP hierarchy are similarly related to a level- decoupling equation. We
also consider the master equation for the -reduced KP hierarchies. Several
comments are made on a possible relation of the generalized master equation to
{\it scaled} Kontsevich-type matrix integrals and on the form the equation
takes in higher genera.Comment: 23pp (REVISED VERSION, 10 April 1992
The intergalactic medium thermal history at redshift z=1.7--3.2 from the Lyman alpha forest: a comparison of measurements using wavelets and the flux distribution
We investigate the thermal history of the intergalactic medium (IGM) in the
redshift interval z=1.7--3.2 by studying the small-scale fluctuations in the
Lyman alpha forest transmitted flux. We apply a wavelet filtering technique to
eighteen high resolution quasar spectra obtained with the Ultraviolet and
Visual Echelle Spectrograph (UVES), and compare these data to synthetic spectra
drawn from a suite of hydrodynamical simulations in which the IGM thermal state
and cosmological parameters are varied. From the wavelet analysis we obtain
estimates of the IGM thermal state that are in good agreement with other
recent, independent wavelet-based measurements. We also perform a reanalysis of
the same data set using the Lyman alpha forest flux probability distribution
function (PDF), which has previously been used to measure the IGM
temperature-density relation. This provides an important consistency test for
measurements of the IGM thermal state, as it enables a direct comparison of the
constraints obtained using these two different methodologies. We find the
constraints obtained from wavelets and the flux PDF are formally consistent
with each other, although in agreement with previous studies, the flux PDF
constraints favour an isothermal or inverted IGM temperature-density relation.
We also perform a joint analysis by combining our wavelet and flux PDF
measurements, constraining the IGM thermal state at z=2.1 to have a temperature
at mean density of T0/[10^3 K]=17.3 +/- 1.9 and a power-law temperature-density
relation exponent gamma=1.1 +/- 0.1 (1 sigma). Our results are consistent with
previous observations that indicate there may be additional sources of heating
in the IGM at z<4.Comment: 15 pages, 14 figures, matches version accepted for publication on
MNRA
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