648 research outputs found
Temperature Dependence of Thermopower in Strongly Correlated Multiorbital Systems
Temperature dependence of thermopower in the multiorbital Hubbard model is
studied by using the dynamical mean-field theory with the non-crossing
approximation impurity solver. It is found that the Coulomb interaction, the
Hund coupling, and the crystal filed splitting bring about non-monotonic
temperature dependence of the thermopower, including its sign reversal. The
implication of our theoretical results to some materials is discussed.Comment: 3 pages, 3 figure
Generalized Conformal Symmetry and Oblique AdS/CFT Correspondence for Matrix Theory
The large N behavior of Matrix theory is discussed on the basis of the
previously proposed generalized conformal symmetry. The concept of `oblique'
AdS/CFT correspondence, in which the conformal symmetry involves both the
space-time coordinates and the string coupling constant, is proposed. Based on
the explicit predictions for two-point correlators, possible implications for
the Matrix-theory conjecture are discussed.Comment: LaTeX, 10 pages, 2 figures, written version of the talk presented at
Strings'9
Future Foam
We study pocket universes which have zero cosmological constant and
non-trivial boundary topology. These arise from bubble collisions in eternal
inflation. Using a simplified dust model of collisions we find that boundaries
of any genus can occur. Using a radiation shell model we perform analytic
studies in the thin wall limit to show the existence of geometries with a
single toroidal boundary. We give plausibility arguments that higher genus
boundaries can also occur. In geometries with one boundary of any genus a
timelike observer can see the entire boundary. Geometries with multiple
disconnected boundaries can also occur. In the spherical case with two
boundaries the boundaries are separated by a horizon. Our results suggest that
the holographic dual description for eternal inflation, proposed by Freivogel,
Sekino, Susskind and Yeh, should include summation over the genus of the base
space of the dual conformal field theory. We point out peculiarities of this
genus expansion compared to the string perturbation series.Comment: 23 pages, 6 figure
Scalar Three-point Functions in a CDL Background
Motivated by the FRW-CFT proposal by Freivogel, Sekino, Susskind and Yeh, we
compute the three-point function of a scalar field in a Coleman-De Luccia
instanton background. We first compute the three-point function of the scalar
field making only very mild assumptions about the scalar potential and the
instanton background. We obtain the three-point function for points in the FRW
patch of the CDL instanton and take two interesting limits; the limit where the
three points are near the boundary of the hyperbolic slices of the FRW patch,
and the limit where the three points lie on the past lightcone of the FRW
patch. We expand the past lightcone three-point function in spherical
harmonics. We show that the near boundary limit expansion of the three-point
function of a massless scalar field exhibits conformal structure compatible
with FRW-CFT when the FRW patch is flat. We also compute the three-point
function when the scalar is massive, and explain the obstacles to generalizing
the conjectured field-operator correspondence of massless fields to massive
fields.Comment: 42 pages + appendices, 10 figures; v2, v3: minor correction
Nonlocality vs. complementarity: a conservative approach to the information problem
A proposal for resolution of the information paradox is that "nice slice"
states, which have been viewed as providing a sharp argument for information
loss, do not in fact do so as they do not give a fully accurate description of
the quantum state of a black hole. This however leaves an information
*problem*, which is to provide a consistent description of how information
escapes when a black hole evaporates. While a rather extreme form of
nonlocality has been advocated in the form of complementarity, this paper
argues that is not necessary, and more modest nonlocality could solve the
information problem. One possible distinguishing characteristic of scenarios is
the information retention time. The question of whether such nonlocality
implies acausality, and particularly inconsistency, is briefly addressed. The
need for such nonlocality, and its apparent tension with our empirical
observations of local quantum field theory, may be a critical missing piece in
understanding the principles of quantum gravity.Comment: 11 pages of text and figures, + references. v2 minor text. v3 small
revisions to match final journal versio
Entropy Creation in Relativistic Heavy Ion Collisions
We review current ideas on entropy production during the different stages of
a relativistic nuclear collision. This includes recent results on decoherence
entropy and the entropy produced during the hydrodynamic phase by viscous
effects. We start by a discussion of decoherence caused by gluon bremsstrahlung
in the very first interactions of gluons from the colliding nuclei. We then
present a general framework, based on the Husimi distribution function, for the
calculation of entropy growth in quantum field theories, which is applicable to
the early ("glasma") phase of the collision during which most of the entropy is
generated. The entropy calculated from the Husimi distribution exhibits linear
growth when the quantum field contains unstable modes and the growth rateis
asymptotically equal to the Kolmogorov-Sina\"i (KS) entropy. We outline how the
approach can be used to investigate the problem of entropy production in a
relativistic heavy-ion reaction from first principles. Finally we discuss some
recent results on entropy production in the strong coupling limit, as obtained
from AdS/CFT duality.Comment: 34 pages, 14 figure
- …