Panagiota Kanti

BLACK HOLES IN THEORIES WITH LARGE EXTRA DIMENSIONS: A REVIEW

We start by reviewing the existing literature on the creation of black holes during high-energy particle collisions, both in the absence and in the presence of extra, compact, spacelike dimensions. Then, we discuss in detail the properties of the produced higher-dimensional black holes, namely the horizon radius, temperature and life-time, as well as the physics that governs the evaporation of these objects, through the emission of Hawking radiation. We first study the emission of visible Hawking radiation on the brane: we derive a master equation for the propagation of fields with arbitrary spin in the induced-on-the-brane black hole background, and we review all existing results in the literature for the emission of scalars, fermions and gauge bosons during the spin-down and Schwarzschild phases of the life of the black hole. Both analytical and numerical results for the graybody factors and radiation spectra are reviewed and exact results for the number and type of fields emitted on the brane as a function of the dimensionality of space–time are discussed. We finally study the emission of Hawking radiation in the bulk: graybody factors and radiation spectra are presented for the emission of scalar modes, and the ratio of the missing energy over the visible one is calculated for different values of the number of extra dimensions.

Calculable corrections to brane black hole decay: The scalar case

It is a remarkable fact that in brane-world theories the true scale M * of quantum gravity may be substantially lower than the traditional Planck scale M pl , possibly approaching the TeV scale, and this radical departure from the standard picture is not excluded @1 #~ for earlier works on brane theories, see @2#!. This observation has naturally excited a large amount of activity investigating both the structure of these theories and their experimental signals @3#. One of the most striking consequences of lowering the Planck scale to the TeV region is that the properties of small black holes are substantially altered @4#. A black hole of given mass M is now much lighter, larger, and colder than a usual black hole of the same mass, provided only that the Schwarschild radius r H of the black hole ~BH! is smaller than the size of the extra dimensions r H,R. In this limit, the black hole is well described as a (4 1n)-dimensional black hole centered on the brane, but extending out into the n extra dimensions. The horizon radius r H of such a black hole is @4,5#

Hawking radiation from a (4+n)-dimensional black hole: Exact results for the Schwarzschild phase.

We start our analysis by deriving a master equation that describes the motion of a field with arbitrary spin s on a 3-brane embedded in a non-rotating, uncharged (4+n)-dimensional black hole background. By numerical analysis, we derive exact results for the greybody factors and emission rates for scalars, fermions and gauge bosons emitted directly on the brane, for all energy regimes and for an arbitrary number n of extra dimensions. The relative emissivities on the brane for different types of particles are computed and their dependence on the dimensionality of spacetime is demonstrated — we therefore conclude that both the amount and the type of radiation emitted can be used for the determination of n if the Hawking radiation from these black holes is observed. The emission of scalar modes in the bulk from the same black holes is also studied and the relative bulk-to-brane energy emissivity is accurately computed. We demonstrate that this quantity varies considerably with n but always remains smaller than unity — this provides firm support to earlier arguments made by Emparan, Horowitz and Myers.

Calculable Corrections to Brane Black Hole Decay II: Greybody Factors for Spin 1/2 and 1

The production of black holes in extra-dimensional brane-world theories can lead to detectable signals via the Hawking evaporation of the black hole to brane-localised Standard Model modes. We calculate, as a function of partial wave number and number of toroidally compactied extra dimensions, the leading correction to the energy spectrum of such Hawking radiation (the greybody factors) for decay into spin 1/2 fermions and spin 1 gauge elds localised on the Standard Model brane. We derive the associated improved dierential emission rates for both types of elds. We provide both simple expressions for the leading behavior of the greybody factors in the low-energy limit !rH 1, and numerical evaluation of our full analytic expressions for the emission rates, valid for !rH 1. The full analytic expressions demonstrate that both the greybody factors and emission rates are enhanced as the number of extra dimensions increases.

Static solutions for brane models with a bulk scalar field

Abstract We present static solutions of the 5-dimensional Einstein equations in the brane-world scenario by using two different approaches for the stabilization of the extra dimension. Assuming a “phenomenological” stabilization mechanism, that creates a non-vanishing T 5 5 in the bulk, we construct a two-brane model, which allows both branes to have positive self-energies. We then consider a candidate theory for the dynamical stabilization, through the introduction of a massless scalar field in the bulk, which interacts with the branes. We find exact static solutions for the metric and scalar field in the bulk and demonstrate that the inter-brane distance is determined by the parameters of scalar field-brane interactions. However, these solutions are always accompanied by a correlation between the bulk cosmological constant, the brane self-energies and the interaction terms of the scalar field with the branes and thus cannot be considered as candidates for the phenomenologically viable stabilized geometry. We find that the aforementioned correlation cannot be avoided even in the case of a single-brane solution with positive self-energy where the fifth dimension ends on a singularity.

On the realization of assisted inflation

We consider conditions necessary for a successful implementation of the so-called assisted inflation. We generalize the applicability of assisted inflation beyond exponential potentials as originally proposed to include standard chaotic ({lambda}{phi}{sup 4} or m{sup 2}{phi}{sup 2}) models as well. We also demonstrate that in a purely four-dimensional theory, unless the assisted sector is in fact decoupled, the additional fields of the assisted sector actually impede inflation. As a specific example of an assisted sector, we consider a five-dimensional Kaluza-Klein (KK) model for which the extra dimension may be somewhat or much larger than the inverse Planck scale. In this case, the assisted sector (coming from a KK compactification) eliminates the need for a fine-tuned quartic coupling to drive chaotic inflation. This is a general result of models with one or more {open_quotes}large{close_quotes} extra dimensions. {copyright} {ital 1999} {ital The American Physical Society}

Single brane cosmological solutions with a stable compact extra dimension

We consider 5-dimensional cosmological solutions of a single brane. The correct cosmology on the brane, i.e., governed by the standard 4-dimensional Friedmann equation, and stable compactification of the extra dimension is guaranteed by the existence of a non-vanishing \hat{T}^5_5 which is proportional to the 4-dimensional trace of the energy-momentum tensor. We show that this component of the energy-momentum tensor arises from the backreaction of the dilaton coupling to the brane. The same positive features are exhibited in solutions found in the presence of non-vanishing cosmological constants both on the brane (\Lambda_{br}) and in the bulk (\Lambda_B). Moreover, the restoration of the Friedmann equation, with the correct sign, takes place for both signs of

Intersecting branes flip SU(5)

\Lambda_B

Assisted chaotic inflation in higher dimensional theories

so long as the sign of

Black Holes at the LHC

\Lambda_{br}