42,805 research outputs found

### Stress-energy Tensor Correlators in N-dim Hot Flat Spaces via the Generalized Zeta-Function Method

We calculate the expectation values of the stress-energy bitensor defined at
two different spacetime points $x, x'$ of a massless, minimally coupled scalar
field with respect to a quantum state at finite temperature $T$ in a flat
$N$-dimensional spacetime by means of the generalized zeta-function method.
These correlators, also known as the noise kernels, give the fluctuations of
energy and momentum density of a quantum field which are essential for the
investigation of the physical effects of negative energy density in certain
spacetimes or quantum states. They also act as the sources of the
Einstein-Langevin equations in stochastic gravity which one can solve for the
dynamics of metric fluctuations as in spacetime foams. In terms of
constitutions these correlators are one rung above (in the sense of the
correlation -- BBGKY or Schwinger-Dyson -- hierarchies) the mean (vacuum and
thermal expectation) values of the stress-energy tensor which drive the
semiclassical Einstein equation in semiclassical gravity. The low and the high
temperature expansions of these correlators are also given here: At low
temperatures, the leading order temperature dependence goes like $T^{N}$ while
at high temperatures they have a $T^{2}$ dependence with the subleading terms
exponentially suppressed by $e^{-T}$. We also discuss the singular behaviors of
the correlators in the $x'\rightarrow x$ coincident limit as was done before
for massless conformal quantum fields.Comment: 23 pages, no figures. Invited contribution to a Special Issue of
Journal of Physics A in honor of Prof. J. S. Dowke

### Monopoles and Knots in Skyrme Theory

We show that the Skyrme theory actually is a theory of monopoles which allows
a new type of solitons, the topological knots made of monopole-anti-monopole
pair,which is different from the well-known skyrmions. Furthermore, we derive a
generalized Skyrme action from the Yang-Mills action of QCD, which we propose
to be an effective action of QCD in the infra-red limit. We discuss the
physical implications of our results.Comment: 4 pages. Phys. Rev. Lett. in pres

### Black hole quasinormal modes using the asymptotic iteration method

In this article we show that the asymptotic iteration method (AIM) allows one
to numerically find the quasinormal modes of Schwarzschild and Schwarzschild de
Sitter (SdS) black holes. An added benefit of the method is that it can also be
used to calculate the Schwarzschild anti-de Sitter (SAdS) quasinormal modes for
the case of spin zero perturbations. We also discuss an improved version of the
AIM, more suitable for numerical implementation.Comment: 10 pages, LaTeX; references added; substantially expanded versio

### Vacuum Structure of Two-Dimensional $\phi^4$ Theory on the Orbifold $S^{1}/Z_{2}$

We consider the vacuum structure of two-dimensional $\phi^4$ theory on
$S^{1}/Z_{2}$ both in the bosonic and the supersymmetric cases. When the size
of the orbifold is varied, a phase transition occurs at $L_{c}=2\pi/m$, where
$m$ is the mass of $\phi$. For $L<L_{c}$, there is a unique vacuum, while for
$L>L_{c}$, there are two degenerate vacua. We also obtain the 1-loop quantum
corrections around these vacuum solutions, exactly in the case of $L<L_{c}$ and
perturbatively for $L$ greater than but close to $L_{c}$. Including the
fermions we find that the "chiral" zero modes around the fixed points are
different for $LL_{c}$. As for the quantum corrections, the
fermionic contributions cancel the singular part of the bosonic contributions
at L=0. Then the total quantum correction has a minimum at the critical length
$L_{c}$.Comment: Revtex, 15 pages, 3 eps figure

### Graviton emission from simply rotating Kerr-de Sitter black holes: Transverse traceless tensor graviton modes

In this article we present results for tensor graviton modes (in seven
dimensions and greater, $n\geq 3$) for greybody factors of Kerr-dS black holes
and for Hawking radiation from simply rotating (n+4)-dimensional Kerr black
holes. Although there is some subtlety with defining the Hawking temperature of
a Kerr-dS black hole, we present some preliminary results for emissions
assuming the standard Hawking normalization and a Bousso-Hawking-like
normalization.Comment: 12 pages, 18 figure

### Angular Eigenvalues of Higher-Dimensional Kerr-(A)dS Black Holes with Two Rotations

In this paper, following the work of Chen, L\"u and Pope, we present the
general metric for Kerr-(A)dS black holes with two rotations. The corresponding
Klein-Gordon equation is separated explicitly, from which we develop
perturbative expansions for the angular eigenvalues in powers of the rotation
parameters with $D\geq 6$.Comment: 10 pages, no figures. To appear in the proceedings of 2011 Shanghai
Asia-Pacific School and Workshop on Gravitatio

### Bulk dominated fermion emission on a Schwarzschild background

Using the WKBJ approximation, and the Unruh method, we obtain semi-analytic
expressions for the absorption probability (in all energy regimes) for Dirac
fermions on a higher dimensional Schwarzschild background. We present an
analytic expression relating the absorption probability to the absorption
cross-section, and then use these results to plot the emission rates to third
order in the WKBJ approximation. The set-up we use is sufficiently general such
that it could also easily be applied to any spherically symmetric background in
$d$-dimensions. Our results lead to the interesting conclusion that for $d>5$
bulk fermion emission dominates brane localised emission. This is an example
contrary to the conjecture that black holes radiate mainly on the brane.Comment: 13 pages, 3 figure

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