13,597 research outputs found
Corrections to the Gell-Mann-Oakes-Renner relation and chiral couplings and
Next to leading order corrections to the
Gell-Mann-Oakes-Renner relation (GMOR) are obtained using weighted QCD Finite
Energy Sum Rules (FESR) involving the pseudoscalar current correlator. Two
types of integration kernels in the FESR are used to suppress the contribution
of the kaon radial excitations to the hadronic spectral function, one with
local and the other with global constraints. The result for the pseudoscalar
current correlator at zero momentum is , leading to the chiral corrections to GMOR: . The resulting uncertainties are mostly due to variations in the upper
limit of integration in the FESR, within the stability regions, and to a much
lesser extent due to the uncertainties in the strong coupling and the strange
quark mass. Higher order quark mass corrections, vacuum condensates, and the
hadronic resonance sector play a negligible role in this determination. These
results confirm an independent determination from chiral perturbation theory
giving also very large corrections, i.e. roughly an order of magnitude larger
than the corresponding corrections in chiral . Combining
these results with our previous determination of the corrections to GMOR in
chiral , , we are able to determine two low
energy constants of chiral perturbation theory, i.e. , and , both at the
scale of the -meson mass.Comment: Revised version with minor correction
Chiral corrections to the Gell-Mann-Oakes-Renner relation
The next to leading order chiral corrections to the
Gell-Mann-Oakes-Renner (GMOR) relation are obtained using the pseudoscalar
correlator to five-loop order in perturbative QCD, together with new finite
energy sum rules (FESR) incorporating polynomial, Legendre type, integration
kernels. The purpose of these kernels is to suppress hadronic contributions in
the region where they are least known. This reduces considerably the systematic
uncertainties arising from the lack of direct experimental information on the
hadronic resonance spectral function. Three different methods are used to
compute the FESR contour integral in the complex energy (squared) s-plane, i.e.
Fixed Order Perturbation Theory, Contour Improved Perturbation Theory, and a
fixed renormalization scale scheme. We obtain for the corrections to the GMOR
relation, , the value . This result
is substantially more accurate than previous determinations based on QCD sum
rules; it is also more reliable as it is basically free of systematic
uncertainties. It implies a light quark condensate . As a byproduct, the chiral perturbation theory (unphysical) low energy
constant is predicted to be , or .Comment: A comment about the value of the strong coupling has been added at
the end of Section 4. No change in results or conslusion
Is there evidence for dimension-two corrections in QCD two-point functions?
The ALEPH data on the (non-strange) vector and axial-vector spectral
functions, extracted from tau-lepton decays, is used in order to search for
evidence for a dimension-two contribution, , to the Operator Product
Expansion (other than quark mass terms). This is done by means of a
dimension-two Finite Energy Sum Rule, which relates QCD to the experimental
hadronic information. The average is
remarkably stable against variations in the continuum threshold, but depends
rather strongly on . Given the current wide spread in the values
of , as extracted from different experiments, we would
conservatively conclude from our analysis that is consistent with zero.Comment: A misprint in Eq. (14) has been corrected. No other changes. Paper to
appear in Phys. Rev.
A Physical Model for SN 2001ay, a normal, bright, extremely slowly declining Type Ia supernova
We present a study of the peculiar Type Ia supernova 2001ay (SN 2001ay). The
defining features of its peculiarity are: high velocity, broad lines, and a
fast rising light curve, combined with the slowest known rate of decline. It is
one magnitude dimmer than would be predicted from its observed value of
Delta-m15, and shows broad spectral features. We base our analysis on detailed
calculations for the explosion, light curves, and spectra. We demonstrate that
consistency is key for both validating the models and probing the underlying
physics. We show that this SN can be understood within the physics underlying
the Delta-m15 relation, and in the framework of pulsating delayed detonation
models originating from a Chandrasekhar mass, white dwarf, but with a
progenitor core composed of 80% carbon. We suggest a possible scenario for
stellar evolution which leads to such a progenitor. We show that the unusual
light curve decline can be understood with the same physics as has been used to
understand the Delta-m15 relation for normal SNe Ia. The decline relation can
be explained by a combination of the temperature dependence of the opacity and
excess or deficit of the peak luminosity, alpha, measured relative to the
instantaneous rate of radiative decay energy generation. What differentiates SN
2001ay from normal SNe Ia is a higher explosion energy which leads to a shift
of the Ni56 distribution towards higher velocity and alpha < 1. This result is
responsible for the fast rise and slow decline. We define a class of SN
2001ay-like SNe Ia, which will show an anti-Phillips relation.Comment: 35 pages, 14 figures, ApJ, in pres
Up and down quark masses from Finite Energy QCD sum rules to five loops
The up and down quark masses are determined from an optimized QCD Finite
Energy Sum Rule (FESR) involving the correlator of axial-vector divergences, to
five loop order in Perturbative QCD (PQCD), and including leading
non-perturbative QCD and higher order quark mass corrections. This FESR is
designed to reduce considerably the systematic uncertainties arising from the
(unmeasured) hadronic resonance sector, which in this framework contributes
less than 3-4% to the quark mass. This is achieved by introducing an
integration kernel in the form of a second degree polynomial, restricted to
vanish at the peak of the two lowest lying resonances. The driving hadronic
contribution is then the pion pole, with parameters well known from experiment.
The determination is done in the framework of Contour Improved Perturbation
Theory (CIPT), which exhibits a very good convergence, leading to a remarkably
stable result in the unusually wide window , where
is the radius of the integration contour in the complex energy (squared)
plane. The results are: MeV, MeV, and Mev (at a scale Q=2 GeV).Comment: Additional references to lattice QCD results have been adde
A determination of the LMC dark matter subhalo mass using the MW halo stars in its gravitational wake
Our goal is to study the gravitational effects caused by the passage of the
Large Magellanic Cloud (LMC) in its orbit on the stellar halo of the Milky Way
(MW). We employed the Gaia Data Release 3 to construct a halo tracers data set
consisting of K-Giant stars and RR-Lyrae variables. Additionally, we have
compared the data with a theoretical model to estimate the DM subhalo mass. We
have improved the characterisation of the local wake and the collective
response due to the LMC orbit. On the other hand, we have estimated for the
first time the dark subhalo mass of the Large Magellanic Cloud, of the order of
M, comparable to previously reported values in the
literature.Comment: submitted to A&
A -ray determination of the Universe's star-formation history
The light emitted by all galaxies over the history of the Universe produces
the extragalactic background light (EBL) at ultraviolet, optical, and infrared
wavelengths. The EBL is a source of opacity for rays via photon-photon
interactions, leaving an imprint in the spectra of distant -ray
sources. We measure this attenuation using {739} active galaxies and one
gamma-ray burst detected by the {\it Fermi} Large Area Telescope. This allows
us to reconstruct the evolution of the EBL and determine the star-formation
history of the Universe over 90\% of cosmic time. Our star-formation history is
consistent with independent measurements from galaxy surveys, peaking at
redshift . Upper limits of the EBL at the epoch of re-ionization
suggest a turnover in the abundance of faint galaxies at .Comment: Published on Science. This is the authors' version of the manuscrip
Mixing angle of doubly heavy baryons in QCD
We calculate the mixing angles between the spin--1/2,
-- and -- states of
doubly heavy baryons within the QCD sum rules method. It is found that the
mixing angles are large and have the values
and , respectively. The mixing angles are
slightly smaller compared to the predictions of the non--relativistic quark
model, and .Comment: 6 Page
Investigation of heavy-heavy pseudoscalar mesons in thermal QCD Sum Rules
We investigate the mass and decay constant of the heavy-heavy pseudoscalar,
, and mesons in the framework of finite temperature QCD
sum rules. The annihilation and scattering parts of spectral density are
calculated in the lowest order of perturbation theory. Taking into account the
additional operators arising at finite temperature, the nonperturbative
corrections are also evaluated. The masses and decay constants remain unchanged
under , but after this point, they start to diminish with
increasing the temperature. At critical or deconfinement temperature, the decay
constants reach approximately to 35% of their values in the vacuum, while the
masses are decreased about 7%, 12% and 2% for , and
states, respectively. The results at zero temperature are in a good consistency
with the existing experimental values as well as predictions of the other
nonperturbative approaches.Comment: 11 Pages, 2 Tables and 6 Figure
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