63 research outputs found
Bridging the static patches: de Sitter holography and entanglement
In the context of de Sitter static-patch holography, two prescriptions have
been put forward for holographic entanglement entropy computations, the
monolayer and bilayer proposals. In this paper, we reformulate both
prescriptions in a covariant way and extend them to include quantum
corrections. We argue that the bilayer proposal is self-consistent, while the
monolayer proposal exhibits contradictory behavior. In fact, the bilayer
proposal leads to a stronger holographic description, in which the full
spacetime is encoded on two screens at the cosmological horizons. At the
classical level, we find large degeneracies of minimal extremal homologous
surfaces, localized at the horizons, which can be lifted by quantum
corrections. The entanglement wedges of subregions of the screens exhibit
non-trivial behaviors, hinting at the existence of interesting phase
transitions and non-locality in the holographic theory. In particular, while
each screen encodes its corresponding static patch, we show that the
entanglement wedge of the screen with the larger quantum area extends and
covers the causal diamond between the screens, with a phase transition
occurring when the quantum areas of the screens become equal. We argue that the
capacity of the screens to encode the region between them is lost, when these
are pushed further in the static patches of the observers and placed on
stretched horizons.Comment: 83 pages, 11 figures. Published versio
Closed FRW holography: A time-dependent ER=EPR realization
We extend a recent de Sitter holographic proposal and entanglement entropy
prescription to generic closed FRW cosmologies in arbitrary dimensions, and
propose that for large classes of bouncing and Big Bang/Big Crunch cosmologies,
the full spacetime can be encoded holographically on two holographic screens,
associated to two antipodal observers. In the expanding phase, the two screens
lie at the apparent horizons. In the contracting phase, there is an infinite
number of possible trajectories of the holographic screens, which can be
grouped in equivalence classes. In each class the effective holographic theory
can be derived from a pair of ``parent'' screens on the apparent horizons. A
number of cases including moduli-dominated cosmologies escape our discussion,
and it is expected that two antipodal observers and their associated screens do
not suffice to reconstruct these cosmologies. The leading contributions to the
entanglement entropy between the screens arise from a minimal extremal trapped
or anti-trapped surface lying in the region between them. This picture entails
a time-dependent realization of the ER=EPR conjecture, where an effective
geometrical bridge connecting the screens via the minimal extremal surface
emerges from entanglement. For the Big Crunch contracting cases, the screens
disentangle and the geometrical bridge closes off when the minimal extremal
trapped sphere hits the Big Crunch singularity at a finite time before the
collapse of the Universe. Semiclassical, thermal corrections are incorporated
in the cases of radiation-dominated cosmologies.Comment: 72 pages, 16 figures, 3 appendice
Massless D-strings and moduli stabilization in type I cosmology
We consider the cosmological evolution induced by the free energy F of a gas
of maximally supersymmetric heterotic strings at finite temperature and weak
coupling in dimension D>=4. We show that F, which plays the role of an
effective potential, has minima associated to enhanced gauge symmetries, where
all internal moduli can be attracted and dynamically stabilized. Using the fact
that the heterotic/type I S-duality remains valid at finite temperature and can
be applied at each instant of a quasi-static evolution, we find in the dual
type I cosmology that all internal NS-NS and RR moduli in the closed string
sector and the Wilson lines in the open string sector can be stabilized. For
the special case of D=6, the internal volume modulus remains a flat direction,
while the dilaton is stabilized. An essential role is played by light D-string
modes wrapping the internal manifold and whose contribution to the free energy
cannot be omitted, even when the type I string is at weak coupling. As a
result, the order of magnitude of the internal radii expectation values on the
type I side is (lambda_I alpha')^{1/2}, where lambda_I is the ten-dimensional
string coupling. The non-perturbative corrections to the type I free energy can
alternatively be described as effects of "thermal E1-instantons", whose
worldsheets wrap the compact Euclidean time cycle.Comment: 39 pages, 1 figur
Inflationary de Sitter solutions from superstrings
In the framework of superstring compactifications with N=1 supersymmetry
spontaneously broken, (by either geometrical fluxes, branes or else), we show
the existence of new inflationary solutions. The time-trajectory of the scale
factor of the metric a, the supersymmetry breaking scale m=m(Phi) and the
temperature T are such that am and aT remain constant. These solutions request
the presence of special moduli-fields: i) The universal "no-scale-modulus" Phi,
which appears in all N=1 effective supergravity theories and defines the
supersymmetry breaking scale m(Phi). ii) The modulus Phi_s, which appears in a
very large class of string compactifications and has a Phi-dependent kinetic
term. During the time evolution, a^4 rho_s remains constant as well, (rho_s
being the energy density induced by the motion of Phi_s). The cosmological term
Lambda(am), the curvature term k(am, aT) and the radiation term c_R=a^4 rho are
dynamically generated in a controllable way by radiative and temperature
corrections; they are effectively constant during the time evolution. Depending
on Lambda, k and c_R, either a first or second order phase transition can occur
in the cosmological scenario. In the first case, an instantonic Euclidean
solution exists and connects via tunneling the inflationary evolution to
another cosmological branch. The latter starts with a big bang and, in the case
the transition does not occur, ends with a big crunch. In the second case, the
big bang and the inflationary phase are smoothly connected.Comment: 37 pages, 4 eps figure
Thermal duality and non-singular cosmology in d-dimensional superstrings
We are presenting the basic ingredients of a stringy mechanism able to
resolve both the Hagedorn instabilities of finite temperature superstrings as
well as the initial singularity of the induced cosmology in arbitrary
dimensions. These are shown to be generic in a large class of (4,0) type II
superstring vacua, where non-trivial "gravito-magnetic" fluxes lift the
Hagedorn instabilities of the thermal ensemble and the temperature duality
symmetry is restored. This symmetry implies a universal maximal critical
temperature. In all such models there are three characteristic regimes, each
with a distinct effective field theory description: Two dual asymptotically
cold regimes associated with the light thermal momentum and light thermal
winding states, and the intermediate regime where additional massless thermal
states appear. The partition function exhibits a conical structure as a
function of the thermal modulus, irrespective of the space-time dimension.
Thanks to asymptotic right-moving supersymmetry, the genus-1 partition function
is well-approximated by that of massless thermal radiation in all of the three
effective field theory regimes. The resulting time-evolution describes a
bouncing cosmology connecting, via spacelike branes, a contracting thermal
"winding" Universe to an expanding thermal "momentum" Universe, free of any
essential curvature singularities. The string coupling remains perturbative
throughout the cosmological evolution. Bouncing cosmologies are presented for
both zero and negative spatial curvature.Comment: 39+1 pages, 2 figure
Induced superstring cosmologies and moduli stabilization
We extend the analysis of the recently obtained stringy cosmological
solutions induced by thermal and quantum effects, once space-time supersymmetry
is spontaneously broken by geometrical fluxes. Cases in which more than one
modulus participating in the supersymmetry breaking mechanism are investigated.
The free energy is obtained at the full string level. In the intermediate
cosmological region where the temperature and the supersymmetry breaking scale
are sufficiently smaller than the Hagedorn temperature, the quantum and thermal
corrections are under control and calculable. The reason is that the
contributions to the effective potential of the moduli that are not
participating in the supersymmetry breaking are exponentially suppressed. The
backreaction on the initially flat background results in many cases into
cosmological evolutions, where the dynamics of all complex structure moduli is
frozen. The solutions describe effectively a radiation dominated era, where
thermal effects are never negligible, even if the temperature tends to zero at
late times. We analyze several types of supersymmetry breaking patterns and
examine the stability of the corresponding radiation era.Comment: 37 pages, 5 figure
Resolution of Hagedorn singularity in superstrings with gravito-magnetic fluxes
We consider closed type II and orientifold backgrounds where supersymmetry is
spontaneously broken by asymmetric geometrical fluxes. We show that these can
be used to describe thermal ensembles with chemical potentials associated to
"gravito-magnetic" fluxes. The thermal free energy is computed at the one-loop
string level, and it is shown to be free of the usual Hagedorn-like
instabilities for a certain choice of the chemical potentials. In the closed
string gravitational sector, as well as in the open string matter sector of the
proposed orientifold construction, the free energy turns out to have
"Temperature duality" symmetry, , which requires interchanging the space-time spinor representations
. For small temperatures, , the anti-spinor
decouples from the spectrum while for large temperatures, , the
spinor decouples. In both limits the free energy vanishes, as we recover a
conventional type II superstring theory. At the self dual point , the
thermal spectra of and are identical. Moreover, there are extra
massless scalars in the adjoint representation of an SO(4) non-abelian gauge
symmetry in the closed-string sector, and open-string massless states charged
simultaneously under both the Chan-Paton and the closed-string SO(4) gauge
group.Comment: LaTeX, 1+23 pages. v2 Section 2.1 expanded. Misprints corrected. To
appear in Nuclear Physics
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