121,611 research outputs found
String Thermodynamics in D-Brane Backgrounds
We discuss the thermal properties of string gases propagating in various
D-brane backgrounds in the weak-coupling limit, and at temperatures close to
the Hagedorn temperature. We determine, in the canonical ensemble, whether the
Hagedorn temperature is limiting or non-limiting. This depends on the
dimensionality of the D-brane, and the size of the compact dimensions. We find
that in many cases the non-limiting behaviour manifest in the canonical
ensemble is modified to a limiting behaviour in the microcanonical ensemble and
show that, when there are different systems in thermal contact, the energy
flows into open strings on the `limiting' D-branes of largest dimensionality.
Such energy densities may eventually exceed the D-brane intrinsic tension. We
discuss possible implications of this for the survival of Dp-branes with large
values of p in an early cosmological Hagedorn regime. We also discuss the
general phase diagram of the interacting theory, as implied by the holographic
and black-hole/string correspondence principles.Comment: 50 pages, LaTeX, 4 eps figures. Added discussion of random walk
picture. Corrected technical error in the treatment of ND strings (notice
some formulas are rewritten). Conclusions unchange
On Stringy Thresholds in SYM/AdS Thermodynamics
We consider aspects of the role of stringy scales and Hagedorn temperatures
in the correspondence between various field theories and AdS-type spaces. The
boundary theory is set on a toroidal world-volume to enable small scales to
appear in the supergravity backgrounds also for low field-theory temperatures.
We find that thermodynamical considerations tend to favour background manifolds
with no string-size characteristic scales. The gravitational dynamics censors
the reliable exposure of Hagedorn physics on the supergravity side, and the
system does not allow the study of the Hagedorn scale by low-temperature field
theories. These results are obtained following some heuristic assumptions on
the character of stringy modifications to the gravitational backgrounds. A rich
phenomenology appears on the supergravity side, with different string
backgrounds dominating in different regions, which should have field-theoretic
consequences. Six-dimensional world volumes turn out to be borderline cases
from several points of view. For lower dimensional world-volumes, a fully
holographic behaviour is exhibited to order 1/N^2, and open strings in their
presence are found to have a thermodynamical Hagedorn behaviour similar to that
of closed strings in flat space.Comment: 49 pages, harvmac, seven Postscript figure
Emission rates, the Correspondence Principle and the Information Paradox
When we vary the moduli of a compactification it may become entropically
favourable at some point for a state of branes and strings to rearrange itself
into a new configuration. We observe that for the elementary string with two
large charges such a rearrangement happens at the `correspondence point' where
the string becomes a black hole. For smaller couplings it is entropically
favourable for the excitations to be vibrations of the string, while for larger
couplings the favoured excitations are pairs of solitonic 5-branes attached to
the string; this helps resolve some recently noted difficulties with matching
emission properties of the string to emission properties of the black hole. We
also examine the change of state when a black hole is placed in a spacetime
with an additional compact direction, and the size of this direction is varied.
These studies suggest a mechanism that might help resolve the information
paradox.Comment: harvmac, 28 page
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