36 research outputs found

### Holographic Higgs Phases

We discuss phases of gauge theories in the holographic context, and formulate
a criterion for the existence of a Higgs phase, where the gauge redundancy is
"spontaneously broken", in purely bulk language. This condition, the existence
of a finite tension solitonic string representing a narrow magnetic flux tube,
is necessary for a bulk theory to be interpreted as a Higgs phase of a boundary
gauge theory. We demonstrate the existence of such solitons in both top-down
and bottom-up examples of holographic theories. In particular, we numerically
construct new solitonic solutions in AdS black hole background, for various
values of the boundary gauge coupling, which are used to demonstrate that the
bulk theory models a superconductor, rather than a superfluid. The criterion we
find is expected to be useful in finding holographic duals of color
superconducting phases of gauge theories at finite density.Comment: Corrected typo

### Modification of late time phase structure by quantum quenches

The consequences of the sudden change in the coupling constants (quenches) on
the phase structure of the theory at late times are explored. We study in
detail the three dimensional phi^6 model in the large N limit, and show that
the phi^6 coupling enjoys a widened range of stability compared to the static
scenario. Moreover, a new massive phase emerges, which for sufficiently large
coupling becomes the dominant vacuum. We argue that these novel phenomena
cannot be described by a simple thermalization effect or the emergence of a
single effective temperature.Comment: 11 pages, 3 figure

### An axisymmetric generalized harmonic evolution code

We describe the first axisymmetric numerical code based on the generalized
harmonic formulation of the Einstein equations which is regular at the axis. We
test the code by investigating gravitational collapse of distributions of
complex scalar field in a Kaluza-Klein spacetime. One of the key issues of the
harmonic formulation is the choice of the gauge source functions, and we
conclude that a damped wave gauge is remarkably robust in this case. Our
preliminary study indicates that evolution of regular initial data leads to
formation both of black holes with spherical and cylindrical horizon
topologies. Intriguingly, we find evidence that near threshold for black hole
formation the number of outcomes proliferates. Specifically, the collapsing
matter splits into individual pulses, two of which travel in the opposite
directions along the compact dimension and one which is ejected radially from
the axis. Depending on the initial conditions, a curvature singularity develops
inside the pulses.Comment: 21 page, 18 figures. v2: minor corrections, added references, new
Fig. 9; journal version

### Quantum Effects of the Conformal Anomaly in a 2D Model of Gravitational Collapse

The macroscopic effects of the quantum conformal anomaly are evaluated in a
simplified two-dimensional model of gravitational collapse. The effective
action and stress tensor of the anomaly can be expressed in a local quadratic
form by the introduction of a scalar conformalon field which satisfies a linear
wave equation. A wide class of non-vacuum initial state conditions is generated
by different solutions of this equation. An interesting subclass of solutions
corresponds to initial states that give rise to an arbitrarily large
semi-classical stress tensor on the future horizon of the black hole formed in
classical collapse. These lead to modification and suppression of Hawking
radiation at late times after the collapse, and potentially large backreaction
effects on the horizon scale due to the conformal anomaly. The probability of
non-vacuum initial conditions large enough to produce these effects is
estimated from the Gaussian vacuum wave functional in the Schrodinger
representation and shown to be of order 1. These results indicate that quantum
effects of the conformal anomaly in non-vacuum states are relevant for
gravitational collapse in the effective theory of gravity in four dimensions as
well.Comment: 40 pages, 5 figure

### Striped Order in AdS/CFT

We study the formation of inhomogeneous order in the Einstein-Maxwell-axion
system, dual to a 2+1 dimensional field theory that exhibits a spontaneously
generated current density, momentum density and modulated scalar operator.
Below the critical temperature, the Reissner-Nordstrom-AdS black hole becomes
unstable and stripes form in the bulk and on the boundary. The bulk geometry
possesses striking geometrical features, including a modulated horizon that
tends to pinch off as T -> 0. On a domain of fixed length, we find a second
order phase transition to the striped solution in each of the grand canonical,
canonical and microcanonical ensembles, with modulated charges that grow and
saturate as we lower the temperature and descend into the inhomogeneous phase.
For the black hole on an infinite domain, a similar second order transition
occurs, and the width of the dominant stripe increases in the zero temperature
limit.Comment: 51 pages, 22 figure