3,468 research outputs found

### Long-distance behavior of $q\bar{q}$ color dependent potentials at finite temperature

SU(3) heavy quark potentials at finite temperature are studied with quenched
lattice QCD using the stochastic gauge-fixing method. In addition to the
standard color average channel, we investigate $q\bar{q}$ potentials in singlet
and octet channels. % We obtain clear signals in all cases. The singlet
$q\bar{q}$ channel yields an attractive force, while the octet $q\bar{q}$
potential is repulsive; the corresponding color average channel also results in
an attractive force. %As the temperature increases, these forces are weakened
and As the temperature increases, these forces become weak and their variations
are very small; at $T/T_c=1.8-5.6$, % the singlet attractive force is not so
weakened even for long distances. the singlet attractive force survives over $R
\sim 1/T$. The singlet and octet potentials calculated with this algorithm have
a small gauge dependence when the gauge parameter $\alpha$ is changed from 0.6
to 1.3.Comment: 12 pages, 9 figures, typos corrected, to appear in Prog. Theor. Phy

### Improved gauge action on an anisotropic lattice II - Anisotropy parameter in the medium coupling region -

The quantum correction of the anisotropy parameter, $\eta$, is calculated for
$\xi=2$ and 3 in the $\beta$ region where numerical simulations such as hadron
spectroscopy are currently carried out, for the improved actions composed of
plaquette and rectangular 6-link loops. The $\beta$ dependences of $\eta$ for
the renormalization group improved actions are quite different from those of
the standard and Symanzik actions. In Iwasaki and DBW2 actions, $\eta$ stays
almost constant in a wide range of $\beta$, which also differs from the
one-loop perturbative result, while in the case of Symanzik action, it
increases as $\beta$ decreases, which is qualitatively similar to the
perturbative result, but the slope is steeper. In the calculation of the $\eta$
parameter close to and in the confined phase, we have applied the link
integration method to suppress the fluctuation of the gauge fields. Some
technical details are summarized.Comment: 21 pages, 10 figure

### Imaginary Chemical Potential Approach for the Pseudo-Critical Line in the QCD Phase Diagram with Clover-Improved Wilson Fermions

The QCD phase diagram is studied in the lattice QCD simulation with the
imaginary chemical potential approach. We employ a clover-improved Wilson
fermion action of two-flavors and a renormalization-group improved gauge
action, and perform the simulation at an intermediate quark mass on a
$8^3\times 4$ lattice. The QCD phase diagram in the imaginary chemical
potential $\mu_I$ region is investigated by performing the simulation for more
than 150 points on the $(\beta,\mu_I)$ plane. We find that the Roberge-Weiss
phase transition at $\mu_I/T=\pi/3$ is first order and its endpoint is second
order, which are identified by the phase of the Polyakov loop. We determine the
pseudo-critical line from the susceptibility of the Polyakov loop modulus. We
find a clear deviation from a linear dependence of the pseudo-critical line on
$\mu_I^2$.Comment: 10 pages, 20 figures, 3 tables. Revtex4. References are added and,
discussions are sharpene

### Simulations of one-flavor QCD at finite temperature by RHMC

We simulate one-flavor QCD with standard Wilson fermions at finite
temperature by the rational hybrid Monte Carlo algorithm. In the heavy quark
region when we decrease the quark mass there is an endpoint which terminates
the first order phase transition. We try to locate it by calculating the Binder
cumulant of the Polyakov loop norm. We estimate the end-point to be kappa_c
\sim 0.07-0.08.Comment: 7 pages, Presented at the XXV International Symposium on Lattice
Field Theory, July 30 - August 4 2007, Regensburg, German

### Measuring Speed of Gravitational Waves by Observations of Photons and Neutrinos from Compact Binary Mergers and Supernovae

Detection of gravitational waves (GW) provides us an opportunity to test
general relativity in strong and dynamical regimes of gravity. One of the tests
is checking whether GW propagates with the speed of light or not. This test is
crucial because the velocity of GW has not ever been directly measured.
Propagation speed of a GW can deviate from the speed of light due to the
modification of gravity, graviton mass, and the nontrivial spacetime structure
such as extra dimensions and quantum gravity effects. Here we report a simple
method to measure the propagation speed of a GW by directly comparing arrival
times between gravitational waves, and neutrinos from supernovae or photons
from short gamma-ray bursts. As a result, we found that the future
multimessenger observations of a GW, neutrinos, and photons can test the GW
propagation speed with the precision of ~10^{-16} improving the previous
suggestions by 8-10 orders of magnitude. We also propose a novel method that
distinguishes the true signal due to the deviation of GW propagation speed from
the speed of light and the intrinsic time delay of the emission at a source by
looking at the redshift dependence.Comment: 8 pages, 6 figure

### Wilson Fermion Determinant in Lattice QCD

We present a formula for reducing the rank of Wilson fermions from $4 N_c N_x
N_y N_z N_t$ to $4 N_c N_x N_y N_z$ keeping the value of its determinant. We
analyse eigenvalues of a reduced matrix and coefficients $C_n$ in the fugacity
expansion of the fermion determinant $\sum_n C_n (\exp(\mu/T))^n$, which play
an important role in the canonical formulation, using lattice QCD
configurations on a $4^4$ lattice. Numerically, $\log |C_n|$ varies as $N_x N_y
N_z$, and goes easily over the standard numerical range; We give a simple cure
for that. The phase of $C_n$ correlates with the distribution of the Polyakov
loop in the complex plain. These results lay the groundwork for future finite
density calculations in lattice QCD.Comment: 20 pages, 2 tables, 32 figure

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