77 research outputs found
Unbounded entropy in spacetimes with positive cosmological constant
In theories of gravity with a positive cosmological constant, we consider
product solutions with flux, of the form (A)dS_p x S^q. Most solutions are
shown to be perturbatively unstable, including all uncharged dS_p x S^q
spacetimes. For dimensions greater than four, the stable class includes
universes whose entropy exceeds that of de Sitter space, in violation of the
conjectured "N-bound". Hence, if quantum gravity theories with
finite-dimensional Hilbert space exist, the specification of a positive
cosmological constant will not suffice to characterize the class of spacetimes
they describe.Comment: 25 pages; v2: references adde
Dynamic critical phenomena at a holographic critical point
We study time-dependent perturbations to a family of five-dimensional black
hole spacetimes constructed as a holographic model of the QCD phase diagram. We
use the results to calculate two transport coefficients, the bulk viscosity and
conductivity, as well as the associated baryon diffusion constant, throughout
the phase diagram. Near the critical point in the T-mu plane, the transport
coefficients remain finite, although their derivatives diverge, and the
diffusion goes to zero. This provides further evidence that large-N_c gauge
theories suppress convective transport. We also find a divergence in the
low-temperature bulk viscosity, outside the region expected to match QCD, and
compare the results to the transport behavior of known R-charged black holes.Comment: 40 pages, 11 figures, LaTe
D3-brane Vacua in Stabilized Compactifications
D3-branes feel no force in no-scale flux compactifications of type IIB string
theory, but the nonperturbative effects required to stabilize the Kahler moduli
break the no-scale structure and generate a potential for D3-brane motion,
confining the branes to certain loci. D3-branes away from these loci break
supersymmetry spontaneously, by an F-term. We present the general conditions
for supersymmetric D3-brane vacua in models with a single Kahler modulus, then
explicitly calculate these vacua for D3-branes moving on the tip of the warped
deformed conifold. We find both continuous moduli spaces and isolated vacua. In
addition, we show that anti-D3-branes and D3-branes are localized to the same
regions by the nonperturbative potential, avoiding a potential obstacle to
brane inflation. We apply these results to determine whether angular motion of
a brane in a throat could play an important role in inflation, and find that
any inflation along the angular directions is short-lived because the field
space is very small.Comment: 30 pages, LaTeX. v2: references added, typos fixe
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