Low-energy Absorption Cross Section Research Articles

Absorption cross section in gravity’s rainbow from confluent Heun equation

We investigate the scattering of a massless scalar field by a charged, non-rotating black hole in the presence of gravity’s rainbow. Using the connection coefficients of the confluent Heun equation expressed in terms of the semi-classical confluent conformal blocks and the instanton part of the Nekrasov–Shatashvili free energy, we obtain an asymptotic expansion for the low-energy absorption cross section. Furthermore, we consider the resummation of the instanton contributions to the absorption cross section, which gives the area of the black hole up to a factor of (4/3)2 .

Absorption cross section in Lifshitz black hole

We derive the absorption cross section of a minimally coupled scalar in the Lifshitz black hole obtained from the new massive gravity. The absorption cross section reduces to the horizon area in the low-energy and massless limits of scalar propagation, indicating that the Lifshitz black hole also satisfies the universality of low-energy absorption cross section for black holes.

Absorption on horizon-wrapped branes

We compute the low energy absorption cross section of space-time scalars on a static D2-brane, in global coordinates, wrapped on the S 2 of an AdS 2×S 2×CY 3 geometry. We discuss its relevance for the construction of the dual quantum mechanics of Calabi-Yau black holes.

Absorption Cross Section and Decay Rate of Stationary Axisymmetric Einstein–Maxwell Dilaton Axion Black Hole

The low energy absorption cross section and the decay rate of the stationary Axisymmetric Einstein–Maxwell Dilaton Axion black hole for massless scalar particles is calculated analytically. It is shown that the partial absorption cross section increases as the rotating parameter a and the absolute value of the dilaton D decreases. It is also shown that the partial absorption cross section is not always positive due to superradiance factor ω–mΩ. However, the decay rate of this black hole is always positive.

Fermion absorption cross section and topology of spherically symmetric black holes

In 1997, Liberati and Pollifrone in [S. Liberati, G. Pollifrone, Phys. Rev. D 56 (1997) 6458, hep-th/9708014] achieved a new formulation of the Bekenstein–Hawking formula, where the entropy and the Euler characteristic are related by S=χA/8. In this work we present a relation between the low-energy absorption cross section for minimally coupled fermions and the Euler characteristic of (3+1)-dimensional spherically symmetric black holes, i.e. σ=χgh−1A. Based on the relation, using the Gauss–Bonnet–Chern theorem and the ϕ-mapping method, an absorption cross section density is introduced to describe the topology of the absorption cross section. It is shown that the absorption cross section and its density are determined by the singularities of the timelike Killing vector field of the spacetime and these singularities carry the topological numbers, Hopf indices and Brouwer degrees, naturally.

Absorption and emission spectra of an higher-dimensional Reissner–Nordström black hole

The absorption and emission problems of the brane-localized and bulk scalars are examined when the spacetime is a ( 4 + n ) -dimensional Reissner–Nordström black hole. Making use of an appropriate analytic continuation, we compute the absorption and emission spectra in the full range of particle's energy. For the case of the brane-localized scalar the presence of the nonzero inner horizon parameter r − generally enhances the absorptivity and suppresses the emission rate compared to the case of the Schwarzschild phase. The low-energy absorption cross section exactly equals to 4 π r + 2 , two-dimensional horizon area. The effect of the extra dimensions generally suppresses the absorptivity and enhances the emission rate, which results in the disappearance of the oscillatory pattern in the total absorption cross section when n is large. For the case of the bulk scalar the effect of r − on the spectra is similar to that in the case of the brane-localized scalar. The low-energy absorption cross section equals to the area of the horizon hypersurface. In the presence of the extra dimensions the total absorption cross section tends to be inclined with a positive slope. It turns out that the ratio of the missing energy over the visible one decreases with increase of r − .

Ratio of absorption cross section for Dirac fermion to that for scalar in the higher-dimensional black hole background

The ratio of the low-energy absorption cross section for Dirac fermion to that for minimally coupled scalar is computed when the spacetimes are various types of the higher-dimensional Reissner–Nordström black holes. It is found that the low-energy absorption cross sections for the Dirac fermion always goes to zero in the extremal limit regardless of the detailed geometry of the spacetime. The physical importance of our results is discussed in the context of the brane-world scenarios and string theories.

On universality of stress-energy tensor correlation functions in supergravity

Using the Minkowski space AdS/CFT prescription we explicitly compute in the low-energy limit the two-point correlation function of the boundary stress-energy tensor in a large class of type IIB supergravity backgrounds with a regular translationally invariant horizon. The relevant set of supergravity backgrounds includes all geometries which can be interpreted via gauge theory/string theory correspondence as being holographically dual to finite temperature gauge theories in Minkowski space–times. The fluctuation–dissipation theorem relates this correlation function computation to the previously established universality of the shear viscosity from supergravity duals, and to the universality of the low energy absorption cross section for minimally coupled massless scalars into a general spherically symmetric black hole. It further generalizes the latter results for the supergravity black brane geometries with non-spherical horizons.

Proof of universality for the absorption of massive scalars by the higher-dimensional Reissner–Nordström black holes

Motivated by black hole experiments as a consequence of the TeV-scale gravity arising from modern brane-world scenarios, we study the absorption problem for the massive scalars when the spacetime background is a ( 4 + n ) -dimensional Reissner–Nordström black hole. For analytic computation we adopt the near-extreme condition in the spacetime background. It is shown that the low-energy absorption cross section for the s-wave case holds an universality, i.e., the absorption cross section equals to the area of the black hole horizon divided by a velocity parameter.

Low-Energy Absorption Cross Section for massive scalar and Dirac fermion by (4 n)-dimensional Schwarzschild Black Hole

Motivated by the brane-world scenarios, we study the absorption problem when the spacetime background is (4+n)-dimensional Schwarzschild black hole. We compute the low-energy absorption cross sections for the brane-localized massive scalar, brane-localized massive Dirac fermion, and massive bulk scalar. For the case of brane-localized massive Dirac fermion we introduce the particle's spin in the traditional Dirac form without invoking the Newman-Penrose method. Our direct introduction of spin enables us to compute contributions to the jth-level partial absorption cross section from orbital angular momenta l = j±1/2. It is shown that the contribution from the low l-level is larger than that from the high l-level in the massive case. In the massless case these two contributions are exactly same with each other. The ratio of low-energy absorption cross sections for Dirac fermion and for scalar is dependent on the number of extra dimensions as 2−(n+3)/(n+1). Thus the ratio factor 1/8 is recovered when n = 0, which Unruh found. The physical importance of this ratio factor is discussed in the context of the brane-world scenario. For the case of bulk scalar our low-energy absorption cross section for S-wave is exactly same with area of the horizon hypersurface in the massless limt, which is an higher-dimensional generaliztion of universality. Our results for all cases turn out to have correct massless and 4d limits.

Effect of scalar mass in the absorption and emission spectra of Schwarzschild black hole

Following Sanchez's approach we investigate the effect of scalar mass in the absorption and emission problems of a four-dimensional (4D) Schwarzschild black hole. The absorption cross sections for arbitrary angular momentum of the scalar field are computed numerically in the full range of energy by making use of the analytic near-horizon and asymptotic solutions and their analytic continuations. The scalar mass has an interesting effect in the low-energy absorption cross section for the S-wave. Unlike the massless case, the cross section decreases with increasing energy in the extremely low-energy regime. As a result the universality, i.e., low-energy cross section for the S-wave is equal to the horizon area, is broken in the presence of mass. If the scalar mass is larger than the critical mass, the absorption cross section becomes a monotonically decreasing function in the entire range of energy. The Hawking emission is also calculated numerically. It turns out that the Planck factor generally suppresses the contribution of higher partial waves except the S-wave. The scalar mass in general tends to reduce the emission rate.

Absorption of dilaton partial waves by D3-branes

We calculate the leading term in the low-energy absorption cross section for an arbitrary partial wave of the dilaton field by a stack of many coincident D3-branes. We find that it precisely reproduces the semiclassical absorption cross section of a 3-brane geometry, including all numerical factors. The crucial ingredient in making the correspondence is the identification of the precise operators on the D3-brane world-volume which couple to the dilaton field and all its derivatives. The needed operators are related through T-duality and the IIA/M-theory correspondence to the recently determined M(atrix) theory expressions for multiple moments of the 11D supercurrent. These operators have a characteristic symmetrized trace structure which plays a key combinatorial role in the analysis for the higher partial waves. The results presented here give new evidence for an infinite family of non-renormalization theorems which are believed to exist for two-point functions in N=4 gauge theory in four dimensions.

Absorption of scalars by extended objects

We derive the low energy absorption cross section of minimal scalars for a very generic class of geometries, that includes, among others, black holes, strings, p-branes, as well as intersecting brane configurations. The scalar field can be absorbed across a regular surface (a horizon) of finite area, or across a zero area throat, which may be singular or regular. Then we focus on some particular cases and compare with the results obtained using microscopic models at weak coupling. Exact agreement is found for the absorption by the non-degenerate ground state of effective strings. For geometries where the throat is singular, we show that absorption through the stretched horizon yields correct results for degenerate states. For non-degenerate (ground) states we introduce a stretched throat, and show that it accounts for the correct dependence on frequency, charges, and moduli for the absorption by ground states of BPS fundamental strings. It is also shown to lead to the correct dependence on frequency for extremal D-branes.

String theory and classical absorption by three-branes

Low-energy absorption cross sections for various particles falling into extreme non-dilatonic branes are calculated using string theory and world-volume field theory methods. The results are compared with classical absorption by the corresponding gravitational backgrounds. For the self-dual three-brane, earlier work by one of us demonstrated precise agreement of the absorption cross sections for the dilaton, and here we extend the result to Ramond-Ramond scalars and to gravitons polarized parallel to the brane. In string theory, the only absorption channel available to dilatons and Ramond-Ramond scalars at leading order is conversion into a pair of gauge bosons on the three-brane. For gravitons polarized parallel to the brane, scalars, fermions and gauge bosons all make leading-order contributions to the cross section, which remarkably add up to the value predicted by classical gravity. For the two-brane and five-brane of M-theory, numerical coefficients fail to agree, signaling our lack of a precise understanding of the world-volume theory for large numbers of coincident branes. In many cases, we note a remarkable isotropy in the final state particle flux within the brane. We also consider the generalization to higher partial waves of minimally coupled scalars. We demonstrate agreement for the three-brane at l = 1 and indicate that further work is necessary to understand l > 1.

Universality of Low Energy Absorption Cross Sections for Black Holes

In this paper we compute the low energy absorption cross-section for minimally coupled massles scalars and spin-$1/2$ particles, into a general spherically symmetric black hole in arbitrary dimensions. The scalars have a cross section equal to the area of the black hole, while the spin-$1/2$ particles give the area measured in a flat spatial metric conformally related to the true metric.