International Journal of Modern Physics A

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.

We extend a path-integral approach to bosonization previously developed in the framework of equilibrium Quantum Field Theories, to the case in which time-dependent interactions are taken into account. In particular we consider a noncovariant version of the Thirring model in the presence of a dynamic barrier at zero temperature. By using the Closed Time Path (Schwinger–Keldysh) formalism, we compute the Green's function and the Total Energy Density of the system. Since our model contains the Tomonaga–Luttinger model as a particular case, we make contact with recent results on nonequilibrium electronic systems.

We calculate ground and several low-lying excited states of various two electron atoms using hyperspherical adiabatic approximation (HAA). Its spectracular accuracy, as compared to exact numerical results of a set of coupled differential equations, demands a better understanding of its mechanism. It is seen that factorizability of the potential matrix into a product of a common function of the global length (hyperradius) and a constant matrix, is responsible for this remarkable success. This is a result of the shape invariance condition in multidimensional supersymmetric quantum mechanics.

We discuss analytic continuation from d-dimensional Lorentzian de Sitter (dS_d) to d-dimensional Lorentzian anti-de Sitter (AdS_d) space–time. We show that AdS_d, with opposite signature of the metric, can be obtained as analytic continuation of a portion of dS_d. This implies that the dynamics of (positive square-mass) scalar particles in AdS_d can be obtained from the dynamics of tachyons in dS_d. We discuss this correspondence both at the level of the solution of the field equations and of the Green functions. The AdS/CFT duality is obtained as analytic continuation of the dS/CFT duality.

We consider effective actions for six-dimensional noncritical superstrings. We show that the addition of N units of RR flux and of N_f space–time filling D5-branes produces AdS₅×S¹ solutions with curvature comparable to the string scale. These solutions have the right structure to be dual to supersymmetric SU(N) gauge theories with N_f flavors. We further suggest bounds on the mass-squared of tachyonic fields in this background that should restrict the theory to the conformal window.

We investigate the influence of the granularity of the lattice on the potential between monopoles. Using the flux definition of monopoles we introduce their centers of mass and are able to realize continuous shifts of the monopole positions. We find periodic deviations from the 1/r-behavior of the monopole-antimonopole potential leading to local extrema. We suppose that these meta-stabilities may influence the order of the phase transition in compact QED.

Using χQM with configuration mixing, the contribution of the gluon polarization to the flavor singlet component of the total spin has been calculated phenomenologically through the relation as defined in the Adler–Bardeen scheme, where ΔΣ on the right-hand side is Q² independent. For evaluation the contribution of gluon polarization , ΔΣ is found in the χQM by fixing the latest E866 data pertaining to asymmetry and the spin polarization functions whereas ΔΣ(Q²) is taken to be 0.30±0.06 and α_s=0.287±0.020, both at Q²=5 GeV². The contribution of gluon polarization Δg' comes out to be 0.33 which leads to an almost perfect fit for spin distribution functions in the χQM. When its implications for magnetic moments are investigated, we find perfect fit for many of the magnetic moments. If an attempt is made to explain the angular momentum sum rule for proton by using the above value of Δg', one finds the contribution of gluon angular momentum to be as important as that of the pairs.

A free test particle in five-dimensional Kaluza–Klein space–time will show its electricity in the reduced four-dimensional space–time when it moves along the fifth dimension. In the light of this observation, we study the coupling of a five-dimensional dust field with the Kaluza–Klein gravity. It turns out that the dust field can curve the five-dimensional space–time in such a way that it provides exactly the source of the electromagnetic field in the four-dimensional space–time after the dimensional reduction.

A value of the cosmological constant in a toy model of the five-dimensional universe is calculated in such a manner that it remains in agreement with both astronomical observations and the quantum field theory concerning the zero-point fluctuations of the vacuum. The (negative) cosmological constant is equal to the inverse of the Planck length squared, which means that in the toy model the vanishing of the observed value of the cosmological constant is a consequence of the existence of an energy cutoff exactly at the Planck level. In turn, a model for both a virtual and a real particle–antiparticle pair is proposed which describes properly some energetic properties of both the vacuum fluctuations and created particles, as well as it allows one to calculate the discrete "bare" values of an elementary particle's mass, electric charge and intrinsic angular momentum (spin) at the energy cutoff. The relationships between the discussed model and some phenomena such as the Zitterbewegung and the Unruh–Davies effect are briefly analyzed, too. The proposed model also allows one to derive the Lorentz transformation and the Maxwell equations while considering the properties of the vacuum filled with the sea of virtual particles and their antiparticles. Finally, the existence of a finite value of the vacuum-energy density resulting from the toy model leads us to the formulation of dimensionless Einstein equations which may be derived from the Lagrangian with a dimensionless (naively renormalized) coupling constant.

Solutions to EYM systems in five space–time dimensions possessing no gravity decoupling limits, feature a peculiar critical behavior which is absent in their six-, seven- and eight-dimensional counterparts which do possess flat space limits. This critical behavior in five dimensions persists even when a scalar matter field is added, rendering the model nontrivial in the gravity decoupling limit. To this end, both regular and black hole spherically symmetric solutions to the higher curvature EYM–Grassmannian sigma model in d=5 space–time dimensions are constructed. A study of the solutions to the Grassmannian model in flat space is also carried out.