11,795 research outputs found
Width and from QCD Light-Cone Sum Rules
We employ the form factors obtained from QCD light-cone sum rules
and calculate the width () in units of
, integrated over the region of accessible momentum transfers,
. Using the most recent BABAR-collaboration
measurements we extract . The sum rule results for the form factors, taken
as an input for a -series parameterization, yield the -shape in the
whole semileptonic region of . We also present the
charged lepton energy spectrum in this decay. Furthermore, the current
situation with is discussed from the QCD point of view. We
suggest to use the ratio of the and widths as an additional test of Standard Model. The
sensitivity of this observable to new physics is illustrated by including a
charged Higgs-boson contribution in the semileptonic decay amplitude.Comment: 22 pages, 8 figures; comments added in section 4, version to be
published in Phys. Rev.
Leptonic decay constants fDs and fD in three flavor lattice QCD
ManuscriptWe determine the leptonic decay constants fDs and fD in three flavor unquenched lattice QCD. We use O(a2)-improved staggered light quarks and O(a)-improved charm quarks in the Fermilab heavy quark formalism. Our preliminary results, based upon an analysis at a single lattice spacing, are fDs = 263+5 −9 ± 24 MeV and fD = 225+11 −13 ± 21 MeV. In each case, the first reported error is statistical while the second is the combined systematic uncertainty
Taking the Universe's Temperature with Spectral Distortions of the Cosmic Microwave Background
The cosmic microwave background (CMB) energy spectrum is a near-perfect
blackbody. The standard model of cosmology predicts small spectral distortions
to this form, but no such distortion of the sky-averaged CMB spectrum has yet
been measured. We calculate the largest expected distortion, which arises from
the inverse Compton scattering of CMB photons off hot, free electrons, known as
the thermal Sunyaev-Zel'dovich (tSZ) effect. We show that the predicted signal
is roughly one order of magnitude below the current bound from the COBE-FIRAS
experiment, but can be detected at enormous significance ()
by the proposed Primordial Inflation Explorer (PIXIE). Although cosmic variance
reduces the effective signal-to-noise to , this measurement will
still yield a sub-percent constraint on the total thermal energy of electrons
in the observable universe. Furthermore, we show that PIXIE can detect subtle
relativistic effects in the sky-averaged tSZ signal at , which
directly probe moments of the optical depth-weighted intracluster medium
electron temperature distribution. These effects break the degeneracy between
the electron density and temperature in the mean tSZ signal, allowing a direct
inference of the mean baryon density at low redshift. Future spectral
distortion probes will thus determine the global thermodynamic properties of
ionized gas in the universe with unprecedented precision. These measurements
will impose a fundamental "integral constraint" on models of galaxy formation
and the injection of feedback energy over cosmic time.Comment: 4.5 pages + references, 2 figures, comments welcome; v2: references
updated; v3: matches PRL accepted versio
Charmonium mass splittings at the physical point
We present results from an ongoing study of mass splittings of the lowest
lying states in the charmonium system. We use clover valence charm quarks in
the Fermilab interpretation, an improved staggered (asqtad) action for sea
quarks, and the one-loop, tadpole-improved gauge action for gluons. This study
includes five lattice spacings, 0.15, 0.12, 0.09, 0.06, and 0.045 fm, with two
sets of degenerate up- and down-quark masses for most spacings. We use an
enlarged set of interpolation operators and a variational analysis that permits
study of various low-lying excited states. The masses of the sea quarks and
charm valence quark are adjusted to their physical values. This large set of
gauge configurations allows us to extrapolate results to the continuum physical
point and test the methodology.Comment: 7 pp, 6 figs, Lattice 201
Low lying charmonium states at the physical point
We present results for the mass splittings of low-lying charmonium states
from a calculation with Wilson clover valence quarks with the Fermilab
interpretation on an asqtad sea. We use five lattice spacings and two values of
the light sea quark mass to extrapolate our results to the physical point.
Sources of systematic uncertainty in our calculation are discussed and we
compare our results for the 1S hyperfine splitting, the 1P-1S splitting and the
P-wave spin orbit and tensor splittings to experiment.Comment: For the Fermilab Lattice and MILC Collaborations; 7 pages, 6 figures;
Contribution to the 32nd International Symposium on Lattice Field Theory,
23-28 June, 2014, Columbia University New York, N
Scaling of stiffness energy for 3d +/-J Ising spin glasses
Large numbers of ground states of 3d EA Ising spin glasses are calculated for
sizes up to 10^3 using a combination of a genetic algorithm and Cluster-Exact
Approximation. A detailed analysis shows that true ground states are obtained.
The ground state stiffness (or domain wall) energy D is calculated. A D ~ L^t
behavior with t=0.19(2) is found which strongly indicates that the 3d model has
an equilibrium spin-glass-paramagnet transition for non-zero T_c.Comment: 4 pages, 4 figure
Existence and uniqueness of the integrated density of states for Schr\"odinger operators with magnetic fields and unbounded random potentials
The object of the present study is the integrated density of states of a
quantum particle in multi-dimensional Euclidean space which is characterized by
a Schr\"odinger operator with a constant magnetic field and a random potential
which may be unbounded from above and from below. For an ergodic random
potential satisfying a simple moment condition, we give a detailed proof that
the infinite-volume limits of spatial eigenvalue concentrations of
finite-volume operators with different boundary conditions exist almost surely.
Since all these limits are shown to coincide with the expectation of the trace
of the spatially localized spectral family of the infinite-volume operator, the
integrated density of states is almost surely non-random and independent of the
chosen boundary condition. Our proof of the independence of the boundary
condition builds on and generalizes certain results by S. Doi, A. Iwatsuka and
T. Mine [Math. Z. {\bf 237} (2001) 335-371] and S. Nakamura [J. Funct. Anal.
{\bf 173} (2001) 136-152].Comment: This paper is a revised version of the first part of the first
version of math-ph/0010013. For a revised version of the second part, see
math-ph/0105046. To appear in Reviews in Mathematical Physic
Gravitational waves from binary systems in circular orbits: Convergence of a dressed multipole truncation
The gravitational radiation originating from a compact binary system in
circular orbit is usually expressed as an infinite sum over radiative multipole
moments. In a slow-motion approximation, each multipole moment is then
expressed as a post-Newtonian expansion in powers of v/c, the ratio of the
orbital velocity to the speed of light. The bare multipole truncation of the
radiation consists in keeping only the leading-order term in the post-Newtonian
expansion of each moment, but summing over all the multipole moments. In the
case of binary systems with small mass ratios, the bare multipole series was
shown in a previous paper to converge for all values v/c < 2/e, where e is the
base of natural logarithms. In this paper, we extend the analysis to a dressed
multipole truncation of the radiation, in which the leading-order moments are
corrected with terms of relative order (v/c)^2 and (v/c)^3. We find that the
dressed multipole series converges also for all values v/c < 2/e, and that it
coincides (within 1%) with the numerically ``exact'' results for v/c < 0.2.Comment: 9 pages, ReVTeX, 1 postscript figur
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