Black Holes in Theories with Large Extra Dimensions: a Review

TL;DR

This review analyzes black hole production and evaporation in theories with Large Extra Dimensions, focusing on how a lowered fundamental gravity scale $M_*$ permits TeV-scale mini black holes to form in high-energy collisions. It develops the higher-dimensional BH framework, including horizon radius and temperature dependences, and then constructs a brane-projected master equation for fields of arbitrary spin to compute brane greybody factors and Hawking spectra, complemented by numerical results for scalar, fermion, and gauge boson emissions. It further examines bulk emissions (scalars and gravitons) and quantifies the bulk-to-brane energy distribution across Schwarzschild and spin-down phases, finding that brane channels dominate for typical $n$ values yet significant bulk energy leakage can occur. The paper highlights the experimental relevance for collider and cosmic-ray searches, the possibility of deducing the number of extra dimensions from radiation spectra, and the limitations of the flat-brane, low-curvature assumptions that underpin the current analyses.

Abstract

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 greybody 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 spacetime are discussed. We finally study the emission of Hawking radiation in the bulk: greybody 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.

Figures (6)

• Figure 1: Analytical results for the greybody factors for emission of (a) scalars, (b) fermions, and (c) gauge bosons from a $(4+n)$-dimensional black hole on the brane.
• Figure 2: Analytical results for the energy emission rates for (a) scalars, (b) fermions, and (c) gauge bosons from a $(4+n)$-dimensional black hole on the brane.
• Figure 3: Numerical results for the greybody factors for emission of (a) scalars, (b) fermions, and (c) gauge bosons from a $(4+n)$-dimensional black hole on the brane.
• Figure 4: Numerical results for the energy emission rates for (a) scalars, (b) fermions, and (c) gauge bosons from a $(4+n)$-dimensional black hole on the brane.
• Figure 5: Energy emission rates for scalars, fermions and gauge bosons for (a)$n=0$, (b)$n=2$, and (c)$n=6$.