arXiv subjects

David A. Lowe

Publications and source records attributed to David A. Lowe.

At least 73 records · Page 4Linked to original sources

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

Stretched horizons, quasiparticles and quasinormal modes

We propose that stretched horizons can be described in terms of a gas of non-interacting quasiparticles. The quasiparticles are unstable, with a lifetime set by the imaginary part of the lowest quasinormal mode frequency. If the horizon arises from an AdS/CFT style duality the quasiparticles are also the effective low-energy degrees of freedom of the finite-temperature CFT. We analyze a large class of models including Schwarzschild black holes, non-extremal Dp-branes, the rotating BTZ black hole and de Sitter space, and we comment on degenerate horizons. The quasiparticle description makes manifest the relationship between entropy and area.

hep-th↗

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↗

arXiv2003

Massive IIA String Theory and Matrix Theory Compactification

We propose a Matrix Theory approach to Romans' massive Type IIA supergravity. It is obtained by applying the procedure of Matrix Theory compactifications to Hull's proposal of the Massive Type IIA String Theory as M-Theory on a twisted torus. The resulting Matrix Theory is a super-Yang Mills theory on large N three-branes with a space dependent non-commutativity parameter, which is also independently derived by a T-duality approach. We give evidence showing that the energies of a class of physical excitations of the super-Yang Mills theory show the correct symmetry expected from Massive Type IIA string theory in a lightcone quantization.

hep-th↗

arXiv2003

Quasiparticle picture of black holes and the entropy--area relation

We propose an effective description of 0-brane black holes, in which the black hole is modeled as a gas of non-interacting quasi-particles in the dual quantum mechanics. This simple model is shown to account for many of the static thermodynamic properties of the black hole. It also accounts for dynamical properties, such as the rate at which energy gets thermalized by the black hole. We use the model to show that the entropy of the quantum mechanics is proportional to the black hole horizon area in Planck units.

hep-th↗

arXiv2002

Hagedorn transition for strings on pp-waves and tori with chemical potentials

It has been conjectured that string theory in a pp-wave background is dual to a sector of N=4 supersymmetric Yang-Mills theory. We study the Hagedorn transition for free strings in this background. We find that the free energy at the transition point is finite suggesting a confinement/deconfinement transition in the gauge theory. In the limit of vanishing mass parameter the free energy matches that of free strings on an 8-torus with momentum/winding chemical potential. The entropy in the microcanonical ensemble with fixed energy and fixed momentum/winding is computed in each case.

hep-th↗

arXiv2002

Probing the Enhancon via Calculations in Supersymmetric Gauge Theory

We consider the N=2 gauge theory on N D7-branes wrapping K3, with D3-brane probes. In the large N limit, the D7-branes blow up to form an enhancon shell. We probe the region inside and outside the enhancon shell using the D3-branes, and compute the probe metric using the Seiberg-Witten formalism. Supergravity arguments suggest a flat interior up to 1/N corrections, and indeed our results for the D3-brane probes are consistent with that. By including the dynamics of the branes, these results, together with those of hep-th/0204050, demonstrate the robustness of the enhancon mechanism beyond patching together of supergravity solutions with D-brane source junction conditions.

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↗

arXiv2002

Moduli Space Metric of N=2 Supersymmetric SU(N) Gauge Theory and the Enhancon

We compute the moduli space metric of SU(N) Yang-Mills theory with N=2 supersymmetry in the vicinity of the point where the classical moduli vanish. This gauge theory may be realized as a set of N D7-branes wrapping a K3 surface, near the enhancon locus. The moduli space metric determines the low-energy worldvolume dynamics of the D7 branes near this point, including stringy corrections. Non-abelian gauge symmetry is not restored on the worldvolume at the enhancon point, but rather the gauge group remains U(1)^{N-1} and light electric and magnetically charged particles coexist. We also study the moduli space metric for a single probe brane in the background of N-1 branes near the enhancon point. We find quantum corrections to the supergravity probe metric that are not suppressed at large separations, but are down by 1/N factors, due to the response of the N-1 enhancon branes to the probe. A singularity appears before the probe reaches the enhancon point where a dyon becomes massless. We compute the masses of W-bosons and monopoles in a large N limit near this critical point.

hep-th↗

arXiv2002

Near-Extremal Black Hole Evaporation in Asymptotically Flat Spacetime

We study black hole evaporation of near-extremal black holes in spherically reduced models with asymptotically Minkowskian spacetime, with the effects of the back-reaction on the geometry included semi-classically. The stress-energy tensor is calculated for null in-falling observers. It is shown that the evaporation proceeds smoothly and there are no instabilities of the outer or inner apparent horizon before the endpoint of evaporation.

hep-th↗

arXiv2001

Forces between stable non-BPS branes

As a step toward constructing realistic brane world models in string theory, we consider the interactions of a pair of non-BPS branes. We construct a dyonic generalization of the non-BPS branes first constructed by Bergman, Gaberdiel and Sen as orbifolds of D-branes on $T^4/\BZ_2$. The force between a dyonic brane and an electric brane is computed and is found to vanish at a nontrivial critical separation. This equilibrium point is unstable. For smaller separations the branes coalesce to form a composite dyonic state, while for larger separations the branes run off to infinity. We suggest generalizations that will lead to potentials with stable local minima.

hep-th↗

arXiv2001

Probing black holes in non-perturbative gauge theory

We use a 0-brane to probe a ten-dimensional near-extremal black hole with N units of 0-brane charge. We work directly in the dual strongly-coupled quantum mechanics, using mean-field methods to describe the black hole background non-perturbatively. We obtain the distribution of W boson masses, and find a clear separation between light and heavy degrees of freedom. To localize the probe we introduce a resolving time and integrate out the heavy modes. After a non-trivial change of coordinates, the effective potential for the probe agrees with supergravity expectations. We compute the entropy of the probe, and find that the stretched horizon of the black hole arises dynamically in the quantum mechanics, as thermal restoration of unbroken U(N+1) gauge symmetry. Our analysis of the quantum mechanics predicts a correct relation between the horizon radius and entropy of a black hole.

hep-th↗

arXiv2001

Black hole entropy from non-perturbative gauge theory

We present the details of a mean-field approximation scheme for the quantum mechanics of N D0-branes at finite temperature. The approximation can be applied at strong 't Hooft coupling. We find that the resulting entropy is in good agreement with the Bekenstein-Hawking entropy of a ten-dimensional non-extremal black hole with 0-brane charge. This result is in accord with the duality conjectured by Itzhaki, Maldacena, Sonnenschein and Yankielowicz. We study the spectrum of single-string excitations within the quantum mechanics, and find evidence for a clear separation between light and heavy degrees of freedom. We also present a way of identifying the black hole horizon.

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↗

arXiv2001

The Stress-Energy Tensor in Soluble Models of Spherically Symmetric Charged Black Hole Evaporation

We study the decay of a near-extremal black hole in AdS$_2$, related to the near-horizon region of 3+1-dimensional Reissner-Nordström spacetime, following Fabbri, Navarro, and Navarro-Salas. Back-reaction is included in a semiclassical approximation. Calculations of the stress-energy tensor of matter coupled to the physical spacetime for an affine null observer demonstrate that the black hole evaporation proceeds smoothly and the near-extremal black hole evolves back to an extremal ground state, until this approximation breaks down.

hep-th↗

arXiv2001

Solving the Hierarchy Problem with Brane Crystals

The brane world scenario advocated by Arkani-Hamed et al. transmutes the hierarchy problem into explaining why extra dimensions have sizes much larger than the fundamental scale. In this paper we discuss possible solutions to this problem by considering the compactified dimensions to be populated by a large number of branes in a crystal lattice. The experimental consequences of this scenario are described, including the presence of large energy gaps in the spectrum of Kaluza-Klein modes.

hep-ph↗

arXiv2000

Black Hole Thermodynamics from Calculations in Strongly-Coupled Gauge Theory

We develop an approximation scheme for the quantum mechanics of N D0-branes at finite temperature in the 't Hooft large-N limit. The entropy of the quantum mechanics calculated using this approximation agrees well with the Bekenstein-Hawking entropy of a ten-dimensional non-extremal black hole with 0-brane charge. This result is in accord with the duality conjectured by Itzhaki, Maldacena, Sonnenschein and Yankielowicz. Our approximation scheme provides a model for the density matrix which describes a black hole in the strongly-coupled quantum mechanics.

hep-th↗

arXiv2000

Yes, semiclassical zero temperature black holes exist

In a recent paper (gr-qc/0002007), Anderson, Hiscock and Taylor claimed that "in all physically realistic cases, macroscopic zero temperature black hole solutions do not exist." We show this conclusion was reached on the basis of an incorrect calculation.

gr-qc↗