963 research outputs found
Markov chain sampling of the loop models on the infinite plane
It was recently proposed in
https://journals.aps.org/pre/abstract/10.1103/PhysRevE.94.043322 [Herdeiro &
Doyon Phys.,Rev.,E (2016)] a numerical method showing a precise sampling of the
infinite plane 2d critical Ising model for finite lattice subsections. The
present note extends the method to a larger class of models, namely the
loop gas models for . We argue that even though the Gibbs measure
is non local, it is factorizable on finite subsections when sufficient
information on the loops touching the boundaries is stored. Our results attempt
to show that provided an efficient Markov chain mixing algorithm and an
improved discrete lattice dilation procedure the planar limit of the
models can be numerically studied with efficiency similar to the Ising case.
This confirms that scale invariance is the only requirement for the present
numerical method to work.Comment: v2: added conclusion section, changes in introduction and appendice
Non-linearities in the quantum multiverse
It has been recently proposed that the multiverse of eternal inflation and
the many-worlds interpretation of quantum mechanics can be identified, yielding
a new view on the measure and measurement problems. In the present note, we
argue that a non-linear evolution of observables in the quantum multiverse
would be an obstacle for such a description and that these non-linearities are
expected from quite general arguments.Comment: 7 page
A Monte Carlo method for critical systems in infinite volume: the planar Ising model
In this paper we propose a Monte Carlo method for generating finite-domain
marginals of critical distributions of statistical models in infinite volume.
The algorithm corrects the problem of the long-range effects of boundaries
associated to generating critical distributions on finite lattices. It uses the
advantage of scale invariance combined with ideas of the renormalization group
in order to construct a type of "holographic" boundary condition that encodes
the presence of an infinite volume beyond it. We check the quality of the
distribution obtained in the case of the planar Ising model by comparing
various observables with their infinite-plane prediction. We accurately
reproduce planar two-, three- and four-point functions of spin and energy
operators. We also define a lattice stress-energy tensor, and numerically
obtain the associated conformal Ward identities and the Ising central charge.Comment: 43 pages, 21 figure
Non-linear Q-clouds around Kerr black holes
Q-balls are regular extended `objects' that exist for some non-gravitating,
self-interacting, scalar field theories with a global, continuous, internal
symmetry, on Minkowski spacetime. Here, analogous objects are also shown to
exist around rotating (Kerr) black holes, as non-linear bound states of a test
scalar field. We dub such configurations Q-clouds. We focus on a complex
massive scalar field with quartic plus hexic self-interactions. Without the
self-interactions, linear clouds have been shown to exist, in synchronous
rotation with the black hole horizon, along 1-dimensional subspaces - existence
lines - of the Kerr 2-dimensional parameter space. They are zero modes of the
superradiant instability. Non-linear Q-clouds, on the other hand, are also in
synchronous rotation with the black hole horizon; but they exist on a
2-dimensional subspace, delimited by a minimal horizon angular velocity and by
an appropriate existence line, wherein the non-linear terms become irrelevant
and the Q-cloud reduces to a linear cloud. Thus, Q-clouds provide an example of
scalar bound states around Kerr black holes which, generically, are not zero
modes of the superradiant instability. We describe some physical properties of
Q-clouds, whose backreaction leads to a new family of hairy black holes,
continuously connected to the Kerr family.Comment: 11 pages, 4 figure
On the interaction between two Kerr black holes
The double-Kerr solution is generated using both a Backlund transformation
and the Belinskii-Zakharov inverse-scattering technique. We build a dictionary
between the parametrisations naturally obtained in the two methods and show
their equivalence. We then focus on the asymptotically flat double-Kerr system
obeying the axis condition which is Z_2^\phi invariant; for this system there
is an exact formula for the force between the two black holes, in terms of
their physical quantities and the coordinate distance. We then show that 1) the
angular velocity of the two black holes decreases from the usual Kerr value at
infinite distance to zero in the touching limit; 2) the extremal limit of the
two black holes is given by |J|=cM^2, where c depends on the distance and
varies from one to infinity as the distance decreases; 3) for sufficiently
large angular momentum the temperature of the black holes attains a maximum at
a certain finite coordinate distance. All of these results are interpreted in
terms of the dragging effects of the system.Comment: 19 pages, 4 figures. v2: changed statement about thermodynamical
equilibrium in section 3; minor changes; added references. v3: added
references to previous relevant work; removed one equation (see note added);
other minor corrections; final version to be published in JHE
n-DBI gravity
n-DBI gravity is a gravitational theory introduced in arXiv:1109.1468
[hep-th], motivated by Dirac-Born-Infeld type conformal scalar theory and
designed to yield non-eternal inflation spontaneously. It contains a foliation
structure provided by an everywhere time-like vector field n, which couples to
the gravitational sector of the theory, but decouples in the small curvature
limit. We show that any solution of Einstein gravity with a particular
curvature property is a solution of n-DBI gravity. Amongst them is a class of
geometries isometric to Reissner-Nordstrom-(Anti) de Sitter black hole, which
is obtained within the spherically symmetric solutions of n-DBI gravity
minimally coupled to the Maxwell field. These solutions have, however, two
distinct features from their Einstein gravity counterparts: 1) the cosmological
constant appears as an integration constant and can be positive, negative or
vanishing, making it a variable quantity of the theory; 2) there is a
non-uniqueness of solutions with the same total mass, charge and effective
cosmological constant. Such inequivalent solutions cannot be mapped to each
other by a foliation preserving diffeomorphism. Physically they are
distinguished by the expansion and shear of the congruence tangent to n, which
define scalar invariants on each leave of the foliation.Comment: 13 page
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