Quantum Aspects of Stimulated Hawking Radiation in an Optical Analog White-Black Hole Pair.

This Letter introduces a synergistic combination of analytical and numerical methods to study the Hawking effect in optical systems containing the analog of a white-black hole pair. Our analytical treatment, based on techniques from Gaussian quantum information, provides a simple and efficient model to describe all aspects of the out-state, including the entanglement between any bipartition. We complement the study with a numerical analysis and apply our tools to investigate the influence that ambient thermal noise and detector inefficiencies have on the out-state. We find that aspects of the Hawking effect that are of quantum origin, i.e., quantum entanglement, are extremely fragile to the influence of inefficiencies and noise. We propose a protocol to amplify and observe these quantum aspects, based on seeding the process with a single-mode squeezed input, opening the door to new possibilities for experimental verification of the Hawking effect.

Potential Gravitational Wave Signatures of Quantum Gravity.

We show that gravitational wave astronomy has the potential to inform us on quantum aspects of black holes. Based on Bekenstein's quantization, we find that black hole area discretization could impart observable imprints to the gravitational wave signal from a pair of merging black holes, affecting their absorption properties during inspiral and their late-time relaxation after merger. In contrast with previous results, we find that black hole rotation, ubiquitous in astrophysics, improves our ability to probe quantum effects. Our analysis shows that gravitational wave echoes and suppressed tidal heating are signs of new physics from which the fundamental quantum of black hole area can be measured, and which are within reach of future detectors. Our results also highlight the need to derive predictions from specific quantum gravity proposals.

Predictions for the Cosmic Microwave Background from an Anisotropic Quantum Bounce.

We introduce an extension of the standard inflationary paradigm on which the big bang singularity is replaced by an anisotropic bounce. Unlike in the big bang model, cosmological perturbations find an adiabatic regime in the past. We show that this scenario accounts for the observed quadrupolar modulation in the temperature anisotropies of the cosmic microwave background, and we make predictions for the polarization angular correlation functions E-E, B-B, and E-B, together with temperature-polarization correlations T-B and T-E, that can be used to test our ideas. We base our calculations on the bounce predicted by loop quantum cosmology, but our techniques and conclusions apply to other bouncing models as well.

Spontaneous Creation of Circularly Polarized Photons in Chiral Astrophysical Systems.

This work establishes a relation between chiral anomalies in curved spacetimes and the radiative content of the gravitational field. In particular, we show that a flux of circularly polarized gravitational waves triggers the spontaneous creation of photons with net circular polarization from the quantum vacuum. Using waveform catalogs, we identify precessing binary black holes as astrophysical configurations that emit such gravitational radiation and then solve the fully nonlinear Einstein's equations with numerical relativity to evaluate the net effect. The quantum amplitude for a merger is comparable to the Hawking emission rate of the final black hole and small to be directly observed. However, the implications for the inspiral of binary neutron stars could be more prominent, as argued on symmetry grounds.

Electromagnetic Duality Anomaly in Curved Spacetimes.

The source-free Maxwell action is invariant under electric-magnetic duality rotations in arbitrary spacetimes. This leads to a conserved classical Noether charge. We show that this conservation law is broken at the quantum level in the presence of a background classical gravitational field with a nontrivial Chern-Pontryagin invariant, in parallel with the chiral anomaly for massless Dirac fermions. Among the physical consequences, the net polarization of the quantum electromagnetic field is not conserved.

Quantum gravity extension of the inflationary scenario.

Since the standard inflationary paradigm is based on quantum field theory on classical space-times, it excludes the Planck era. Using techniques from loop quantum gravity, the paradigm is extended to a self-consistent theory from the Planck scale to the onset of slow roll inflation, covering some 11 orders of magnitude in energy density and curvature. This preinflationary dynamics also opens a small window for novel effects, e.g., a source for non-Gaussianities, which could extend the reach of cosmological observations to the deep Planck regime of the early Universe.

Hawking radiation by Kerr black holes and conformal symmetry.

The exponential blueshift associated with the event horizon of a black hole makes conformal symmetry play a fundamental role in accounting for its thermal properties. Using a derivation based on two-point functions, we show that the full spectrum of thermal radiation of scalar particles by Kerr black holes can be explicitly derived on the basis of a conformal symmetry arising in the wave equation near the horizon. The simplicity of our approach emphasizes the depth of the connection between conformal symmetry and black hole radiance.

Revising the predictions of inflation for the cosmic microwave background anisotropies.

We point out that, if quantum field renormalization is taken into account and the counterterms are evaluated at the Hubble-radius crossing time or few e-foldings after it, the predictions of slow-roll inflation for both the scalar and the tensorial power spectrum change significantly. This leads to a change in the consistency condition that relates the tensor-to-scalar amplitude ratio with spectral indices. A reexamination of the potentials varphi;{2} and varphi;{4} shows that both are compatible with five-year WMAP data. Only when the counterterms are evaluated at much larger times beyond the end of inflation does one recover the standard predictions. The alternative predictions presented here may soon come within the range of measurement of near-future experiments.

Reexamination of the power spectrum in de Sitter inflation.

We find that the amplitude of quantum fluctuations of the invariant de Sitter vacuum coincides exactly with that of the vacuum of a comoving observer for a massless scalar (inflaton) field. We propose redefining the actual physical power spectrum as the difference between the amplitudes of the above vacua. An inertial particle detector continues to observe the Gibbons-Hawking temperature. However, although the resulting power spectrum is still scale-free, its amplitude can be drastically reduced since now, instead of the Hubble's scale at the inflationary period, it is determined by the square of the mass of the inflaton fluctuation field.

Black hole state counting in loop quantum gravity: a number-theoretical approach.

We give an efficient method, combining number-theoretic and combinatorial ideas, to exactly compute black hole entropy in the framework of loop quantum gravity. Along the way we provide a complete characterization of the relevant sector of the spectrum of the area operator, including degeneracies, and explicitly determine the number of solutions to the projection constraint. We use a computer implementation of the proposed algorithm to confirm and extend previous results on the detailed structure of the black hole degeneracy spectrum.

Black hole radiance, short distances, and TeV gravity.

Using a derivation of black hole radiance in terms of two-point functions one can provide a quantitative estimate of the contribution of short distances to the spectrum. Thermality is preserved for black holes with kappalp<<1. However, deviations from the Planckian spectrum can be found for mini black holes in TeV gravity scenarios, even before reaching the Planck phase.