arXiv subjects

Kevin Goldstein

Publications and source records attributed to Kevin Goldstein.

25 records · Page 2Linked to original sources

arXiv2006

A C-Function For Non-Supersymmetric Attractors

We present a c-function for spherically symmetric, static and asymptotically flat solutions in theories of four-dimensional gravity coupled to gauge fields and moduli. The c-function is valid for both extremal and non-extremal black holes. It monotonically decreases from infinity and in the static region acquires its minimum value at the horizon, where it equals the entropy of the black hole. Higher dimensional cases, involving $p$-form gauge fields, and other generalisations are also discussed.

hep-th↗

arXiv2005

Non-Supersymmetric Attractors

We consider theories with gravity, gauge fields and scalars in four-dimensional asymptotically flat space-time. By studying the equations of motion directly we show that the attractor mechanism can work for non-supersymmetric extremal black holes. Two conditions are sufficient for this, they are conveniently stated in terms of an effective potential involving the scalars and the charges carried by the black hole. Our analysis applies to black holes in theories with ${\cal N} \le 1$ supersymmetry, as well as non-supersymmetric black holes in theories with ${\cal N} = 2$ supersymmetry. Similar results are also obtained for extremal black holes in asymptotically Anti-de Sitter space and in higher dimensions.

hep-th↗

arXiv2003

Real-Time Perturbation Theory in de Sitter Space

We consider scalar field theory in de Sitter space with a general vacuum invariant under the continuously connected symmetries of the de Sitter group. We begin by reviewing approaches to define this as a perturbative quantum field theory. One approach leads to Feynman diagrams with pinch singularities in the general case, which renders the theory perturbatively ill-defined. Another approach leads to well-defined perturbative correlation functions on the imaginary time continuation of de Sitter space. When continued to real-time, a path integral with a non-local action generates the time-ordered correlators. Curiously, observables built out of local products of the fields show no sign of this non-locality. However once one couples to gravity, we show acausal effects are unavoidable and presumably make the theory ill-defined. The Bunch-Davies vacuum state is the unique de Sitter invariant state that avoids these problems.

hep-th↗

arXiv2003

Ultra High Energy Cosmic Rays and de Sitter Vacua

The production of ultra high-energy cosmic rays in de Sitter invariant vacuum states is considered. Assuming the present-day universe is asymptoting toward a future de Sitter phase, we argue the observed flux of cosmic rays places a bound on the parameter $α$ that characterizes these de Sitter invariant vacuum states, generalizing earlier work of Starobinsky and Tkachev. If this bound is saturated, we obtain a new top-down scenario for the production of super-GZK cosmic rays. The observable predictions bear many similarities to the previously studied scenario where super-GZK events are produced by decay of galactic halo super-heavy dark matter particles.

astro-ph↗

arXiv2003

A note on alpha-vacua and interacting field theory in de Sitter space

We set up a consistent renormalizable perturbation theory of a scalar field in a nontrivial alpha vacuum in de Sitter space. Although one representation of the effective action involves non-local interactions between anti-podal points, we show the theory leads to causal physics, and we prove a spectral theorem for the interacting two-point function. We construct the renormalized stress energy tensor and show this develops no imaginary part at leading order in the interactions, consistent with stability.

hep-th↗

arXiv2002

Initial state effects on the cosmic microwave background and trans-planckian physics

There exist a one complex parameter family of de Sitter invariant vacua, known as alpha vacua. In the context of slow roll inflation, we show that all but the Bunch-Davies vacuum generates unacceptable production of high energy particles at the end of inflation. As a simple model for the effects of trans-planckian physics, we go on to consider non-de Sitter invariant vacua obtained by patching modes in the Bunch-Davies vacuum above some momentum scale M_c, with modes in an alpha vacuum below M_c. Choosing M_c near the Planck scale M_pl, we find acceptable levels of hard particle production, and corrections to the cosmic microwave perturbations at the level of H M_pl/M_c^2, where H is the Hubble parameter during inflation. More general initial states of this type with H<< M_c << M_pl can give corrections to the spectrum of cosmic microwave background perturbations at order 1. The parameter characterizing the alpha-vacuum during inflation is a new cosmological observable.

hep-th↗

arXiv2001

Stacking non-BPS D-Branes

We present a candidate supergravity solution for a stacked configuration of stable non-BPS D-branes in Type II string theory compactified on T^4/Z_2. This gives a supergravity description of nonabelian tachyon condensation on the brane worldvolume.

hep-th↗