430 research outputs found
Perturbation Calculation of the Axial Anomaly of a Ginsparg-Wilson lattice Dirac operator
A recent proposal suggests that even if a Ginsparg-Wilson lattice Dirac
operator does not possess any topological zero modes in
topologically-nontrivial gauge backgrounds, it can reproduce correct axial
anomaly for sufficiently smooth gauge configurations, provided that it is
exponentially-local, doublers-free, and has correct continuum behavior. In this
paper, we calculate the axial anomaly of this lattice Dirac operator in weak
coupling perturbation theory, and show that it recovers the topological charge
density in the continuum limit.Comment: 25 pages, v2: calculation up to O(g^4) for nonabelian gauge
backgroun
Mass dependence of the hairpin vertex in quenched QCD
The pseudoscalar ``hairpin'' vertex (i.e. quark-disconnected vertex) plays a
key role in quenched chiral perturbation theory. Direct calculations using
lattice simulations find that it has a significant dependence on quark mass. I
show that this mass dependence can be used to determine the quenched
Gasser-Leutwyler constant L5. This complements the calculation of L5 using the
mass dependence of the axial decay constant of the pion. In an appendix, I
discuss power counting for quenched chiral perturbation theory and describe the
particular scheme used in this paper.Comment: 12 pages, 4 figures. Version to appear in Phys. Rev. D. Central
result unchanged, but explanation of calculation improved and minor errors
corrected. New appendix discusses power counting schemes in quenched chiral
perturbation theor
Effect of Sun and Planet-Bound Dark Matter on Planet and Satellite Dynamics in the Solar System
We apply our recent results on orbital dynamics around a mass-varying central
body to the phenomenon of accretion of Dark Matter-assumed not
self-annihilating-on the Sun and the major bodies of the solar system due to
its motion throughout the Milky Way halo. We inspect its consequences on the
orbits of the planets and their satellites over timescales of the order of the
age of the solar system. It turns out that a solar Dark Matter accretion rate
of \approx 10^-12 yr^-1, inferred from the upper limit \Delta M/M= 0.02-0.05 on
the Sun's Dark Matter content, assumed somehow accumulated during last 4.5 Gyr,
would have displaced the planets faraway by about 10^-2-10^1 au 4.5 Gyr ago.
Another consequence is that the semimajor axis of the Earth's orbit,
approximately equal to the Astronomical Unit, would undergo a secular increase
of 0.02-0.05 m yr^-1, in agreement with the latest observational determinations
of the Astronomical Unit secular increase of 0.07 +/- 0.02 m yr^-1 and 0.05 m
yr^-1. By assuming that the Sun will continue to accrete Dark Matter in the
next billions year at the same rate as in the past, the orbits of its planets
will shrink by about 10^-1-10^1 au (\approx 0.2-0.5 au for the Earth), with
consequences for their fate, especially of the inner planets. On the other
hand, lunar and planetary ephemerides set upper bounds on the secular variation
of the Sun's gravitational parameter GM which are one one order of magnitude
smaller than 10^-12 yr^-1. Dark Matter accretion on planets has, instead, less
relevant consequences for their satellites. Indeed, 4.5 Gyr ago their orbits
would have been just 10^-2-10^1 km wider than now. (Abridged)Comment: LaTex2e, 17 pages, no figures, 7 tables, 61 references. Small problem
with a reference fixed. To appear in Journal of Cosmology and Astroparticle
Physics (JCAP
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Orbit correction using virtual monitors at Jefferson Lab
An orbit correction algorithm is developed to achieve the following goals for the CEBAF accelerator at Jefferson Lab.: (1) Pre-processing of orbit input to account for estimated misalignment and monitor errors. (2) Automatic elimination of blind spots caused by response matrix degeneracy. (3) Transparency of exception handling to interchangeable generic steering engines. (4) CEBAF-specific demands on control of injection angle, path length, orbit effects on optics, simultaneous multiple pass steering, and orbit control at un-monitored locations. All of the above can be accomplished by the introduction of virtual monitors into the processed input orbit, whose theoretical basis is to be discussed in this report. Implementation of all or part of these features and operational experience during the CEBAF variable energy runs will also be discussed
Cosmic histories of star formation and reionization: An analysis with a power-law approximation
With a simple power-law approximation of high-redshift () star
formation history, i.e., , we
investigate the reionization of intergalactic medium (IGM) and the consequent
Thomson scattering optical depth for cosmic microwave background (CMB) photons.
A constraint on the evolution index is derived from the CMB optical
depth measured by the {\it Wilkinson Microwave Anisotropy Probe} (WMAP)
experiment, which reads ,
where the free parameter is the number of the escaped
ionizing ultraviolet photons per baryon. Moreover, the redshift for full
reionization, , can also be expressed as a function of as well as
. By further taking into account the implication of the
Gunn-Peterson trough observations to quasars for the full reionization
redshift, i.e., , we obtain
and .
For a typical number of of ionizing photons released per baryon of
normal stars, the fraction of these photons escaping from the stars, , can be constrained to within the range of .Comment: 10 pages, 4 figures, accepted for publication in JCA
Is X(3872) {\sl Really} a Molecular State?
After taking into account both the pion and sigma meson exchange potential,
we have performed a dynamical calculation of the system.
The meson exchange potential is repulsive from heavy quark symmetry
and numerically important for a loosely bound system. Our analysis disfavors
the interpretation of X(3872) as a loosely bound molecular state if we use the
experimental coupling constant and a reasonable cutoff
around 1 GeV, which is the typical hadronic scale. Bound state solutions with
negative eigenvalues for the system exist only with either a
very large coupling constant (two times of the experimental value) or a large
cutoff ( GeV or GeV). In contrast, there
probably exists a loosely bound S-wave molecular state. Once
produced, such a molecular state would be rather stable since its dominant
decay mode is the radiative decay through . Experimental
search of these states will be very interesting.Comment: 11 pages, 7 figures, 9 tables. The version to appear in EPJ
Heavy Quarks and Heavy Quarkonia as Tests of Thermalization
We present here a brief summary of new results on heavy quarks and heavy
quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma
Thermalization" Workshop in Vienna, Austria in August 2005, directly following
the International Quark Matter Conference in Hungary.Comment: 8 pages, 5 figures, Quark Gluon Plasma Thermalization Workshop
(Vienna August 2005) Proceeding
Proximity effect at superconducting Sn-Bi2Se3 interface
We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions
down to 250 mK and in different magnetic fields. A number of conductance
anomalies were observed below the superconducting transition temperature of Sn,
including a small gap different from that of Sn, and a zero-bias conductance
peak growing up at lower temperatures. We discussed the possible origins of the
smaller gap and the zero-bias conductance peak. These phenomena support that a
proximity-effect-induced chiral superconducting phase is formed at the
interface between the superconducting Sn and the strong spin-orbit coupling
material Bi2Se3.Comment: 7 pages, 8 figure
Centrality Dependence of the High p_T Charged Hadron Suppression in Au+Au collisions at sqrt(s_NN) = 130 GeV
PHENIX has measured the centrality dependence of charged hadron p_T spectra
from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T
decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction
of the contribution from hard scattering to high p_T hadron production. For
central collisions the yield at high p_T is shown to be suppressed compared to
binary nucleon-nucleon collision scaling of p+p data. This suppression is
monotonically increasing with centrality, but most of the change occurs below
30% centrality, i.e. for collisions with less than about 140 participating
nucleons. The observed p_T and centrality dependence is consistent with the
particle production predicted by models including hard scattering and
subsequent energy loss of the scattered partons in the dense matter created in
the collisions.Comment: 7 pages text, LaTeX, 6 figures, 2 tables, 307 authors, resubmitted to
Phys. Lett. B. Revised to address referee concerns. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
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