89,353 research outputs found
Production of W and Z bosons accompanied by jets at LHC startup
We report on potential for measurement of W and Z boson production
accompanied by jets at the CMS experiment. Of particular interest are jet
multiplicity and Pt distributions. The 10/pb to 100/pb datasets expected in the
startup year of operation of LHC are likely to already provide information
beyond the reach of the Tevatron collider both in jet multiplicity and Pt
range. We are especially interested in understanding the ratios of W+jets to
Z+jets distributions by comparing them to next-to-leading order Monte Carlo
generators, as these processes present a formidable background for searches of
new physics phenomena.Comment: Poster session at ICHEP08, Philadelphia, USA, July 2008. 3 pages,
LaTeX, 1 jpg figure. Updated with the new latex template for ICHEP0
Smoothness and asymptotic estimates of densities for SDEs with locally smooth coefficients and applications to square root-type diffusions
We study smoothness of densities for the solutions of SDEs whose coefficients
are smooth and nondegenerate only on an open domain . We prove that a smooth
density exists on and give upper bounds for this density. Under some
additional conditions (mainly dealing with the growth of the coefficients and
their derivatives), we formulate upper bounds that are suitable to obtain
asymptotic estimates of the density for large values of the state variable
("tail" estimates). These results specify and extend some results by Kusuoka
and Stroock [J. Fac. Sci. Univ. Tokyo Sect. IA Math. 32 (1985) 1--76], but our
approach is substantially different and based on a technique to estimate the
Fourier transform inspired from Fournier [Electron. J. Probab. 13 (2008)
135--156] and Bally [Integration by parts formula for locally smooth laws and
applications to equations with jumps I (2007) The Royal Swedish Academy of
Sciences]. This study is motivated by existing models for financial securities
which rely on SDEs with non-Lipschitz coefficients. Indeed, we apply our
results to a square root-type diffusion (CIR or CEV) with coefficients
depending on the state variable, that is, a situation where standard techniques
for density estimation based on Malliavin calculus do not apply. We establish
the existence of a smooth density, for which we give exponential estimates and
study the behavior at the origin (the singular point).Comment: Published in at http://dx.doi.org/10.1214/10-AAP717 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The Origin and Shaping of Planetary Nebulae: Putting the Binary Hypothesis to the Test
Planetary nebulae (PNe) are circumstellar gas ejected during an intense
mass-losing phase in the the lives of asymptotic giant branch stars. PNe have a
stunning variety of shapes, most of which are not spherically symmetric. The
debate over what makes and shapes the circumstellar gas of these evolved,
intermediate mass stars has raged for two decades. Today the community is
reaching a consensus that single stars cannot trivially manufacture PNe and
impart to them non spherical shapes and that a binary companion, possibly even
a sub-stellar one, might be needed in a majority of cases. This theoretical
conjecture has however not been tested observationally. In this review we
discuss the problem both from the theoretical and observational standpoints,
explaining the obstacles that stand in the way of a clean observational test
and ways to ameliorate the situation. We also discuss indirect tests of this
hypothesis and its implications for stellar and galactic astrophysics.Comment: 28 pages of text. 4 tables 9 figures. Accepted by PASP Review
Reconstruction of mimetic gravity in a non-singular bouncing universe from quantum gravity
We illustrate a general reconstruction procedure for mimetic gravity.
Focusing on a bouncing cosmological background, we derive general properties
that must be satisfied by the function implementing the limiting
curvature hypothesis. We show how relevant physical information can be
extracted from power law expansions of in different regimes, corresponding
e.g. to the very early universe or to late times. Our results are then applied
to two specific models reproducing the cosmological background dynamics
obtained in group field theory and in loop quantum cosmology, and we discuss
the possibility of using this framework as providing an effective field theory
description of quantum gravity. We study the evolution of anisotropies near the
bounce, and discuss instabilities of scalar perturbations. Furthermore, we
discuss two equivalent formulations of mimetic gravity: one in terms of an
effective fluid with exotic properties, the other featuring two distinct
time-varying gravitational "constants" in the cosmological equations.Comment: Invited article for the special issue "Progress in Group Field Theory
and Related Quantum Gravity Formalisms" of the journal "Universe"; 21 pages,
2 figures; v2: matches published versio
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