76 research outputs found
Transport coefficients and universality in hot strongly coupled gauge theories
The gauge/gravity duality provides a valuable opportunity to study the behavior of relativistic fluids described by some strongly-interacting non-Abelian gauge theories. However, as yet no gravity duals are known for the field theories that are currently used to describe nature. Thus, it is particularly interesting to search for universal properties of theories with gravity duals. This dissertation discusses a broad class of theories with gravity duals, and it is shown that at high temperatures, the speed of sound squared is bounded from above by one-third of the speed of light squared. It is conjectured that this may be a universal property of theories with gravity duals. It is also shown that the temperature dependence of a number of transport coefficients takes a universal form in the high-temperature limit. In particular, in a high-temperature expansion, the power law of the leading correction away from the infinite temperature limit is universal for all of the transport coefficients, and is the same as that of the speed of sound squared
Searching for Fermi Surfaces in Super-QED
The exploration of strongly-interacting finite-density states of matter has
been a major recent application of gauge-gravity duality. When the theories
involved have a known Lagrangian description, they are typically deformations
of large supersymmetric gauge theories, which are unusual from a
condensed-matter point of view. In order to better interpret the
strong-coupling results from holography, an understanding of the weak-coupling
behavior of such gauge theories would be useful for comparison. We take a first
step in this direction by studying several simple supersymmetric and
non-supersymmetric toy model gauge theories at zero temperature. Our
supersymmetric examples are super-QED and
super-QED, with finite densities of electron number and R-charge respectively.
Despite the fact that fermionic fields couple to the chemical potentials we
introduce, the structure of the interaction terms is such that in both of the
supersymmetric cases the fermions do not develop a Fermi surface. One might
suspect that all of the charge in such theories would be stored in the scalar
condensates, but we show that this is not necessarily the case by giving an
example of a theory without a Fermi surface where the fermions still manage to
contribute to the charge density.Comment: 37 pages, 3 figures. V3: minor clarifications added, version to
appear in JHE
Vacuum structure of Yang-Mills theory as a function of
It is believed that in Yang-Mills theory observables are -branched
functions of the topological angle. This is supposed to be due to the
existence of a set of locally-stable candidate vacua, which compete for global
stability as a function of . We study the number of vacua,
their interpretation, and their stability properties using systematic
semiclassical analysis in the context of adiabatic circle compactification on
. We find that while observables are indeed N-branched
functions of , there are only locally-stable candidate
vacua for any given . We point out that the different vacua
are distinguished by the expectation values of certain magnetic line operators
that carry non-zero GNO charge but zero 't Hooft charge. Finally, we show that
in the regime of validity of our analysis YM theory has spinodal points as a
function of , and gather evidence for the conjecture that these
spinodal points are present even in the limit.Comment: 33 pages, 6 figures. v3: added reference
Spectral sum rules for confining large-N theories
We consider asymptotically-free four-dimensional large- gauge theories
with massive fermionic and bosonic adjoint matter fields, compactified on
squashed three-spheres, and examine their regularized large- confined-phase
spectral sums. The analysis is done in the limit of vanishing 't Hooft
coupling, which is justified by taking the size of the compactification
manifold to be small compared to the inverse strong scale . Our
results motivate us to conjecture some universal spectral sum rules for these
large gauge theories.Comment: 25 pages, 2 figures. v2: fixed typos, added references, and some
minor improvements to discussio
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