811 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
String Theory and Hybrid Inflation/Acceleration
We find a description of hybrid inflation in (3+1)-dimensions using brane
dynamics of Hanany-Witten type. P-term inflation/acceleration of the universe
with the hybrid potential has a slow-roll de Sitter stage and a waterfall stage
which leads towards an N=2 supersymmetric ground state. We identify the
slow-roll stage of inflation with a non-supersymmetric `Coulomb phase' with
Fayet-Iliopoulos term. This stage ends when the mass squared of one of the
scalars in the hypermultiplet becomes negative. At that moment the brane system
starts undergoing a phase transition via tachyon condensation to a fully
Higgsed supersymmetric vacuum which is the absolute ground state of P-term
inflation. A string theory/cosmology dictionary is provided, which leads to
constraints on parameters of the brane construction from cosmological
experiments. We display a splitting of mass levels reminiscent of the Zeeman
effect due to spontaneous supersymmetry breaking.Comment: 1+21 pages, 5 figures, LaTeX; one figure added; included computation
of supertrace of mass squared for the string theory and discussion of
relation to spontaneous breaking of supersymmetry; several typos corrected;
references adde
Non-perturbative spinning black holes in dynamical Chern-Simons gravity
Spinning black holes in dynamical Einstein-Chern-Simons gravity are
constructed by directly solving the field equations, without resorting to any
perturbative expansion. This model is obtained by adding to the
Einstein-Hilbert action a particular higher-curvature correction: the
Pontryagin density, linearly coupled to a scalar field. The spinning black
holes are stationary, axi-symmetric, asymptotically flat generalisations of the
Kerr solution of Einstein's gravity, but they possess a non-trivial
(odd-parity) scalar field. They are regular on and outside the horizon and
satisfy a generalized Smarr relation. We discuss the deviations from Kerr at
the level of the spin and mass distribution, the horizon angular velocity, the
ergo-region and some basic properties of geodesic motion. For sufficiently
small values of the Chern-Simons coupling our results match those previously
obtained using a perturbative approach.Comment: 14 pages, 5 figure
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