David I. Santiago

The Generalized Uncertainty Principle and Black Hole Remnants

In the current standard viewpoint small black holes are believed to emit black body radiation at the Hawking temperature, at least until they approach Planck size, after which their fate is open to conjecture. A cogent argument against the existence of remnants is that, since no evident quantum number prevents it, black holes should radiate completely away to photons and other ordinary stable particles and vacuum, like any unstable quantum system. Here we argue the contrary, that the generalized uncertainty principle may prevent their total evaporation in exactly the same way that the uncertainty principle prevents the hydrogen atom from total collapse: the collapse is prevented, not by symmetry, but by dynamics, as a minimum size and mass are approached.

ON GRAVITY AND THE UNCERTAINTY PRINCIPLE

Heisenberg showed in the early days of quantum theory that the uncertainty principle follows as a direct consequence of the quantization of electromagnetic radiation in the form of photons. As we show here the gravitational interaction of the photon and the particle being observed modifies the uncertainty principle with an additional term. From the modified or gravitational uncertainty principle it follows that there is an absolute minimum uncertainty in the position of any particle, of order of the Planck length. A modified uncertainty relation of this form is a standard result of superstring theory, but the derivation given here is based on simpler and rather general considerations with either Newtonian gravitational theory or general relativity theory.

QUANTUM PHASE TRANSITIONS AND THE BREAKDOWN OF CLASSICAL GENERAL RELATIVITY

Abstract It is proposed that the infinite-red-shift surface of a black hole is a quantum phase transition of the vacuum of space-time analogous to the liquid-vapour critical point of a Bose fluid. The equations of classical general relativity remain valid arbitrarily close to the horizon yet fail there through the divergence of a characteristic coherence length Ε. The integrity of global time, required for conventional quantum mechanics to be defined, is maintained. The metric inside the event horizon is different from that predicted by classical general relativity and may be de Sitter space. The deviations from classical behaviour lead to distinct spectroscopic and bolometric signatures that can, in principle, be observed at large distances from the black hole.

Scalar-Tensor Cosmologies and their Late Time Evolution

We study the asymptotic behavior at late times of Friedmann-Robertson-Walker (uniform density) cosmological models within scalar-tensor theories of gravity. Particularly, we analyze the late time behavior in the present (matter dominated) epoch of the universe. The result of Damour and Nordtvedt that for a massless scalar in a flat cosmology the Universe evolves towards a state indistinguishable from general relativity is generalized. We first study a massless scalar field in an open universe. It is found that, while the universe tends to approach a state with less scalar contribution to gravity, the attractor mechanism is not effective enough to drive the theory towards a final state indistinguishable from general relativity. For the self-interacting case it is found that the scalar field potential dominates the late time behavior. In most cases this makes the attractor mechanism effective, thus resulting in a theory of gravity with vanishingly small scalar contribution even for an open universe.

Nucleosynthesis constraints on scalar-tensor theories of gravity

We study the cosmological evolution of massless single-field scalar-tensor theories of gravitation from the time before the onset of

The Gravity Probe B test of general relativity

{e}^{+}{e}^{\ensuremath{-}}

Interplay between gravity and quintessence: a set of new GR solutions

annihilation and nucleosynthesis up to the present. The cosmological evolution together with the observational bounds on the abundances of the lightest elements (those mostly produced in the early universe) place constraints on the coefficients of the Taylor series expansion of

On the Energy-Momentum Tensor of the Scalar Field in Scalar–Tensor Theories of Gravity

a(\ensuremath{\varphi})

Observation and Modeling of the Solar Transition Region. II. Identification of New Classes of Solutions of Coronal Loop Models

, which specifies the coupling of the scalar field to matter and is the only free function in the theory. In the case when

Magnetic instability in strongly correlated superconductors.

a(\ensuremath{\varphi})