10,782 research outputs found
Chiral Phase Transition in Lattice QCD with Wilson Quarks
The nature of the chiral phase transition in lattice QCD is studied for the
cases of 2, 3 and 6 flavors with degenerate Wilson quarks, mainly on a lattice
with the temporal direction extension . We find that the chiral phase
transition is continuous for the case of 2 flavors, while it is of first order
for 3 and 6 flavors.Comment: uuencoded compressed tar file, LaTeX, 14 pages, 7 figure
Post-Oligarchic Evolution of Protoplanetary Embryos and the Stability of Planetary Systems
We investigate the orbit-crossing time (T_c) of protoplanet systems both with
and without a gas-disk background. The protoplanets are initially with equal
masses and separation (EMS systems) scaled by their mutual Hill's radii. In a
gas-free environment, we find log (T_c/yr) = A+B \log (k_0/2.3). Through a
simple analytical approach, we demonstrate that the evolution of the velocity
dispersion in an EMS system follows a random walk. The stochastic nature of
random-walk diffusion leads to (i) an increasing average eccentricity ~
t^1/2, where t is the time; (ii) Rayleigh-distributed eccentricities
(P(e,t)=e/\sigma^2 \exp(-e^2/(2\sigma^2)) of the protoplanets; (iii) a
power-law dependence of T_c on planetary separation. As evidence for the
chaotic diffusion, the observed eccentricities of known extra solar planets can
be approximated by a Rayleigh distribution. We evaluate the isolation masses of
the embryos, which determine the probability of gas giant formation, as a
function of the dust and gas surface densities.Comment: 15 pages, 13 figures (2 color ones), accepted for publication in Ap
QCD Phase Transition with Strange Quark in Wilson Formalism for Fermions
The nature of QCD phase transition is studied with massless up and down
quarks and a light strange quark, using the Wilson formalism for quarks on a
lattice with the temporal direction extension . We find that the phase
transition is first order in the cases of both about 150 MeV and 400 MeV for
the strange quark mass. These results together with those for three degenerate
quarks suggest that QCD phase transition in nature is first order.Comment: uuencoded compressed tar file, LaTeX, 13 pages, 9 figures, Minor
errors for quoting references are corrected and a reference is adde
Quasi-free Standing Epitaxial Graphene on SiC by Hydrogen Intercalation
Quasi-free standing epitaxial graphene is obtained on SiC(0001) by hydrogen
intercalation. The hydrogen moves between the 6root3 reconstructed initial
carbon layer and the SiC substrate. The topmost Si atoms which for epitaxial
graphene are covalently bound to this buffer layer, are now saturated by
hydrogen bonds. The buffer layer is turned into a quasi-free standing graphene
monolayer with its typical linear pi-bands. Similarly, epitaxial monolayer
graphene turns into a decoupled bilayer. The intercalation is stable in air and
can be reversed by annealing to around 900 degrees Celsius.Comment: Accepted for publication in Physical Review Letter
Finite Temperature Transitions in Lattice QCD with Wilson Quarks --- Chiral Transitions and the Influence of the Strange Quark ---
The nature of finite temperature transitions in lattice QCD with Wilson
quarks is studied near the chiral limit for the cases of 2, 3, and 6 flavors of
degenerate quarks (, 3, and 6) and also for the case of massless up and
down quarks and a light strange quark (). Our simulations mainly
performed on lattices with the temporal direction extension indicate
that the finite temperature transition in the chiral limit (chiral transition)
is continuous for , while it is of first order for and 6. We
find that the transition is of first order for the case of massless up and down
quarks and the physical strange quark where we obtain a value of
consistent with the physical value. We also discuss the phase
structure at zero temperature as well as that at finite temperatures.Comment: uuencoded compressed tar file, 70 pages, 32 figure
The string tension in SU(N) gauge theory from a careful analysis of smearing parameters
We report a method to select optimal smearing parameters before production
runs and discuss the advantages of this selection for the determination of the
string tension.Comment: Contribution to Lat97 poster session, title was 'How to measure the
string tension', 3 pages, 5 colour eps figure
Testing improved actions for dynamical Kogut-Susskind quarks
We extend tests of "Naik" and "fat link" improvements of the Kogut-Susskind
quark action to full QCD simulations, and verify that the improvements
previously demonstrated in the quenched approximation apply also to dynamical
quark simulations. We extend the study of flavor symmetry improvement to the
complete set of pions, and find that the nonlocal pions are significantly
heavier than the local non-Goldstone pion. These results can be used to
estimate the lattice spacing necessary for realistic simulations with this
action.Comment: 16 pages, LaTeX, PostScript figures include
A doorway to Borromean halo nuclei: the Samba configuration
We exploit the possibility of new configurations in three-body halo nuclei -
Samba type - (the neutron-core form a bound system) as a doorway to Borromean
systems. The nuclei Be, B, N and F are of such
nature, in particular N with a half-life of 37.7 s and a halo radius of
6.07 fm is an excellent example of Samba-halo configuration. The fusion below
the barrier of the Samba halo nuclei with heavy targets could reveal the so far
elusive enhancement and a dominance of one-neutron over two-neutron transfers,
in contrast to what was found recently for the Borromean halo nucleus He +
U.Comment: Accepted for publication in Modern Physics Letters
Time dependent CP asymmetry in decay to probe the origin of CP violation
Since the CP violation in the system has been investigated up to now only
through processes related to the -- mixing, urgently required is
new way of study for the CP violation and establishing its origin in the
system independent of the mixing process. In this work, we explore the
exclusive decay to obtain the time-dependent CP
asymmetry in decay process in the standard model and the
supersymmetric model. We find that the complex RL and RR mass insertion to the
squark sector in the MSSM can lead to a large CP asymmetry in
decay through the gluino-squark diagrams, which is not predicted in the
Standard Model induced by the -- mixing.Comment: 10 pages, 4 eps figure
Nonstandard optics from quantum spacetime
We study light propagation in the picture of semi-classical space-time that
emerges in canonical quantum gravity in the loop representation. In such
picture, where space-time exhibits a polymer-like structure at microscales, it
is natural to expect departures from the perfect non-dispersiveness of ordinary
vacuum. We evaluate these departures, computing the modifications to Maxwell's
equations due to quantum gravity, and showing that under certain circumstances,
non-vanishing corrections appear that depend on the helicity of propagating
waves. These effects could lead to observable cosmological predictions of the
discrete nature of quantum spacetime. In particular, recent observations of
non-dispersiveness in the spectra of gamma-ray bursts at various energies could
be used to constrain the type of semi-classical state that describes the
universe.Comment: 4 pages, RevTeX, no figure
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