12,656 research outputs found
On the phase of quark determinant in lattice QCD with finite chemical potential
We investigate the phase of the quark determinant with finite chemical
potential in lattice QCD using both analytic and numerical methods. Applying
the winding number expansion and the hopping parameter expansion to the
logarithm of the determinant, we show that the absolute value of the phase has
an upper bound that grows with the spatial volume but decreases exponentially
with an increase in the temporal extent of the lattice. This analytic but
approximate result is confirmed with a numerical study in four-flavor QCD in
which the phase is calculated exactly. Since the phase is well controlled on
lattices with larger time extents, we try the phase reweighting method in a
region beyond where the Taylor expansion method cannot be applied.
Working in four-flavor QCD, we find a first-order like behavior on a lattice at which was previously observed by Kentucky
group with the canonical method. We also show that the winding number expansion
has a nice convergence property beyond . We expect that this expansion
is useful to study the high density region of the QCD phase diagram at low
temperatures.Comment: 21 page
Absolute continuity of symmetric Markov processes
We study Girsanov's theorem in the context of symmetric Markov processes,
extending earlier work of Fukushima-Takeda and Fitzsimmons on Girsanov
transformations of ``gradient type.'' We investigate the most general Girsanov
transformation leading to another symmetric Markov process. This investigation
requires an extension of the forward-backward martingale method of Lyons-Zheng,
to cover the case of processes with jumps.Comment: Published by the Institute of Mathematical Statistics
(http://www.imstat.org) in the Annals of Probability
(http://www.imstat.org/aop/) at http://dx.doi.org/10.1214/00911790400000043
The survival and destruction of X-ray coronae of early-type galaxies in the rich cluster environments: a case study of Abell 1367
A new Chandra observation of the northwest region of the galaxy cluster A1367
reveals four cool galaxy coronae (0.4 - 1.0 keV) embedded in the hot
intracluster medium (ICM) (5 - 6 keV). While the large coronae of NGC 3842 and
NGC 3837 appear symmetric and relaxed, the galaxy coronae of the \lsim L*
galaxies (NGC 3841 and CGCG 97090) are disturbed and being stripped. Massive
galaxies, with dense cooling cores, are better able to resist ram pressure
stripping and survive in rich environments than \lsim L* galaxies whose
galactic coronae are much less dense. The survival of these cool coronae
implies that thermal conduction from the hot surrounding ICM has to be
suppressed by a factor of at least 60, at the corona boundary. Within the
galaxy coronae of NGC 3842 and NGC 3837, stellar mass loss or heat conduction
with the Spitzer value may be sufficient to balance radiative cooling. Energy
deposition at the ends of collimated jets may heat the outer coronae, but allow
the survival of a small, dense gas core (e.g., NGC 3842 in A1367 and NGC 4874
in Coma). The survived X-ray coronae become significantly smaller and fainter
with the increasing ambient pressure.Comment: 11 pages, 7 figures, emulateapj5, accepted by Ap
Location of the Multicritical Point for the Ising Spin Glass on the Triangular and Hexagonal Lattices
A conjecture is given for the exact location of the multicritical point in
the phase diagram of the +/- J Ising model on the triangular lattice. The
result p_c=0.8358058 agrees well with a recent numerical estimate. From this
value, it is possible to derive a comparable conjecture for the exact location
of the multicritical point for the hexagonal lattice, p_c=0.9327041, again in
excellent agreement with a numerical study. The method is a variant of duality
transformation to relate the triangular lattice directly with its dual
triangular lattice without recourse to the hexagonal lattice, in conjunction
with the replica method.Comment: 9 pages, 1 figure; Minor corrections in notatio
Generation of 10^15 - 10^17 eV photons by UHE CR in the Galactic magnetic filed
We show that the deep expected in the diffuse photon spectrum above the
threshold of e+e- pair production, i.e., at energies 10^15 - 10^17 eV, may be
absent due to the synchrotron radiation by the electron component of the
extragalactic Ultra-High Energy Cosmic Rays (UHE CR) in the Galactic magnetic
filed. The mechanism we propose requires small (less than 2x10^-12 G)
extragalactic magnetic fields and large fraction of photons in the UHE CR. For
a typical photon flux expected in top-down scenarios of UHE CR, the predicted
flux in the region of the deep is close to the existing experimental limit. The
sensitivity of our mechanism to the extragalactic magnetic field may be used to
improve existing bounds on the latter by two orders of magnitude.Comment: 11 pages, LaTeX, 1 .ps figure. Numerical error corrected; references
adde
Structural Transition of Li2RuO3 Induced by Molecular-Orbit Formation
A pseudo honeycomb system Li2RuO3 exhibits a second-order-like transition at
temperature T=Tc=540 K to a low-T nonmagnetic phase with a significant lattice
distortion forming Ru-Ru pairs. For this system, we have calculated the band
structure, using the generalized gradient approximation (GGA) in both the high-
and low- T phases, and found that the results of the calculation can naturally
explain the insulating behavior observed in the low-T phase. The detailed
characters of the Ru 4d t2g bands obtained by the tight-binding fit to the
calculated dispersion curves show clear evidence that the structural transition
is driven by the formation of the Ru-Ru molecular-orbits, as proposed in our
previous experimental studies.Comment: 5 pages, 5 figures, 4 tables, submitted to J. Phys. Soc. Jp
Statistics of clustering of ultra-high energy cosmic rays and the number of their sources
Observation of clustering of ultra-high energy cosmic rays (UHECR) suggests
that they are emitted by compact sources. Assuming small deflection of UHECR
during the propagation, the statistical analysis of clustering allows to
estimate the spatial density of the sources, h, including those which have not
yet been observed directly. When applied to astrophysical models involving
extra-galactic sources, the estimate based on 14 events with energy E>10^{20}
eV gives h ~ 6 X 10^{-3} Mps^{-3}. With increasing statistics, this estimate
may lead to exclusion of the models which associate the production of UHECR
with exceptional galaxies such as AGN, powerful radio-galaxies, dead quasars,
and models based on gamma ray bursts.Comment: The version accepted for publication in Phys. Rev. Lett. Notations
changed to conventional ones. The estimate of the effective GZK radius
replaced by the result of numerical simulatio
Anomalous Hall Effect and Magnetoresistance of SrFe1-xCoxO3-d
Transport and magnetic studies on polycrystalline samples of SrFe1-xCoxO3-d
have been carried out to investigate the relationship between the magnetic
structure and the anomalous Hall resistivity rH. The hysteretic behavior of the
magnetization observed in the measurements with varying temperature T up and
then down after zero field cooling indicates that the system has the reentrant
spin-glass phase, which is supported by the increasing width of the magnetic
reflections observed by neutron diffraction with decreasing T below the Curie
temperature TC. Detailed analyses of the observed Hall resistivity rH indicate
that the anomalous Hall coefficient exhibits unusual behavior in the reentrant
spin-glass phase. The magnetic field (H)- and T-dependence of the
magnetoresistance of the present system can be understood by a spin dependent
tunneling model.Comment: 10 pages, 11 figures, J. Phys. Soc. Jpn. 72 (2003) No.
Nonexponential decay of an unstable quantum system: Small--value s-wave decay
We study the decay process of an unstable quantum system, especially the
deviation from the exponential decay law. We show that the exponential period
no longer exists in the case of the s-wave decay with small value, where
the value is the difference between the energy of the initially prepared
state and the minimum energy of the continuous eigenstates in the system. We
also derive the quantitative condition that this kind of decay process takes
place and discuss what kind of system is suitable to observe the decay.Comment: 17 pages, 6 figure
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