8,600 research outputs found
The Weyl tensor two-point function in de Sitter spacetime
We present an expression for the Weyl-Weyl two-point function in de Sitter
spacetime, based on a recently calculated covariant graviton two-point function
with one gauge parameter. We find that the Weyl-Weyl two-point function falls
off with distance like r^{-4}, where r is spacelike coordinate separation
between the two points.Comment: 9 pages, no figure
Stability of Massive Cosmological Gravitons
We analyze the physics of massive spin 2 fields in (A)dS backgrounds and
exhibit that: The theory is stable only for masses m^2 >= 2\Lambda/3, where the
conserved energy associated with the background timelike Killing vector is
positive, while the instability for m^2<2\Lambda/3 is traceable to the helicity
0 energy. The stable, unitary, partially massless theory at m^2=2\Lambda/3
describes 4 propagating degrees of freedom, corresponding to helicities
(+/-2,+/-1) but contains no 0 helicity excitation.Comment: 13 pages, LaTeX, version to appear in Phys. Lett.
Particle Horizon and Warped Phenomenology
Giant resonances of gravity Kaluza-Klein modes (with tensor couplings) in
high energy collisions are expected in the Randall-Sundrum orbifold model that
incorporates a plausible solution to the hierarchy problem. When the model is
extended to incorporate an exponentially small 4-D cosmological constant, the
KK spectrum becomes continuous, even in the compactified case. This is due to
the presence of a particle horizon, which provides a way to evade Weinberg's
argument of the need of fine-tuning to get a very small cosmological constant.Comment: 10 pages, 1 figure, REVTE
Decay of the free-theory vacuum of scalar field theory in de Sitter spacetime in the interaction picture
A free-theory vacuum state of an interacting field theory, e.g. quantum
gravity, is unstable at tree level in general due to spontaneous emission of
Fock-space particles in any spacetime with no global timelike Killing vectors,
such as de Sitter spacetime, in the interaction picture. As an example, the
rate of spontaneous emission of Fock-space particles is calculated in phi^4
theory in de Sitter spacetime. It is possible that this apparent spontaneous
emission does not correspond to any physical processes because the states are
not evolved by the true Hamiltonian in the interaction picture. Nevertheless,
the constant spontaneous emission of Fock-space particles in the interaction
picture clearly demonstrates that the in- and out-vacuum states are orthogonal
to each other as emphasized by Polyakov and that the in-out perturbation
theory, which presupposes some overlap between these two vacuum states, is
inadequate. Other possible implications of apparent vacuum instability of this
kind in the interaction picture are also discussed.Comment: title changed, 7 page
Radiation from a moving Scalar Source
We study classical radiation and quantum bremsstrahlung effect of a moving
point scalar source. Our classical analysis provides another example of
resolving a well-known apparent paradox, that of whether a constantly
accelerating source radiates or not. Quantum mechanically, we show that for a
scalar source with arbitrary motion, the tree level emission rate of scalar
particles in the inertial frame equals the sum of emission and absorption rates
of zero-energy Rindler particles in the Rindler frame. We then explicitly
verify this result for a source undergoing constant proper acceleration.Comment: 15 pages, CU-TP-59
Low-energy sector quantization of a massless scalar field outside a Reissner-Nordstrom black hole and static sources
We quantize the low-energy sector of a massless scalar field in the
Reissner-Nordstrom spacetime. This allows the analysis of processes involving
soft scalar particles occurring outside charged black holes. In particular, we
compute the response of a static scalar source interacting with Hawking
radiation using the Unruh (and the Hartle-Hawking) vacuum. This response is
compared with the one obtained when the source is uniformly accelerated in the
usual vacuum of the Minkowski spacetime with the same proper acceleration. We
show that both responses are in general different in opposition to the result
obtained when the Reissner-Nordstrom black hole is replaced by a Schwarzschild
one. The conceptual relevance of this result is commented.Comment: 12 pages (REVTEX), no figure
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