International Journal of Modern Physics A

We review the theory and phenomenology of effective supergravity theories based on orbifold compactifications of the weakly-coupled heterotic string. In particular, we consider theories in which the four-dimensional theory displays target space modular invariance and where the dilatonic mode undergoes Kähler stabilization. A self-contained exposition of effective Lagrangian approaches to gaugino condensation and heterotic string theory is presented, leading to the development of the models of Binétruy, Gaillard and Wu. Various aspects of the phenomenology of this class of models are considered. These include issues of supersymmetry breaking and superpartner spectra, the role of anomalous U(1) factors, issues of flavor and R-parity conservation, collider signatures, axion physics, and early universe cosmology. For the vast majority of phenomenological considerations the theories reviewed here compare quite favorably to other string-derived models in the literature. Theoretical objections to the framework and directions for further research are identified and discussed.

An intersection of noncommutative geometry and loop quantum gravity is proposed. Alain Connes' noncommutative geometry provides a framework in which the Standard Model of particle physics coupled to general relativity is formulated as a unified, gravitational theory. However, to this day no quantization procedure compatible with this framework is known. In this paper we consider the noncommutative algebra of holonomy loops on a functional space of certain spin-connections. The construction of a spectral triple is outlined and ideas on interpretation and classical limit are presented.

The Coulombic systems (αpe) and (ααe), (αppe), (ααpe) and (Li³⁺Li³⁺e) placed in a magnetic field B ≳ 10¹¹G are studied. It is demonstrated a theoretical existence of the exotic ion (HeH)²⁺ for B ≳ 5 × 10¹²G in parallel configuration (the magnetic field is directed along internuclear axis) as optimal as well as its excited states 1π, 1δ. As for the exotic ion it is shown that in spite of strong electrostatic repulsion of α-particles this ion can also exist for B ≳ 100 a.u. (= 2.35 × 10¹¹G) in parallel configuration as optimal in the states 1σ_g (ground state), 1π_u, 1δ_g. Upon appearance both ions are unstable towards dissociation with He⁺ in the final state but with very large lifetime. However, at B ≳ 10000 a.u., the ion (HeH)²⁺ becomes stable, while at B ≳ 1000 a.u., the ion becomes stable. For both ions the vibrational and rotational energies are calculated. With a magnetic field growth, both exotic ions become more and more tightly bound and compact, their lowest rotational and vibrational energies grow drastically. At the edge of applicability of nonrelativistic approximation, B ~ 4.414 × 10¹³G, there are indications that three more exotic linear ions (H–He–H)³⁺, (He–H–He)⁴⁺ and even in parallel configuration may also occur.

Combination of both quantum field theory (QFT) and string theory in curved backgrounds in a consistent framework, the string analogue model, allows us to provide a full picture of the Kerr–Newman black hole and its evaporation going beyond the current picture. We compute the quantum emission cross-section of strings by a Kerr–Newman black hole (KNbh). It shows the black hole emission at the Hawking temperature T_sem in the early stage of evaporation and the new string emission featuring a Hagedorn transition into a string state of temperature T_s at the last stages. New bounds on J and Q emerge in the quantum string regime (besides the known ones of the classical/semiclassical QFT regime). The last state of evaporation of a semiclassical Kerr–Newman black hole with mass M > m_Pl, angular momentum J and charge Q is a string state of temperature T_s, string mass M_s, J = 0 and Q = 0, decaying as usual quantum strings do into all kinds of particles. (Naturally, in this framework, there is no loss of information, (there is no paradox at all).) We compute the string entropy S_s(m, j) from the microscopic string density of states of mass m and spin mode j, ρ(m, j). (Besides the Hagedorn transition at T_s) we find for high j (extremal string states j → m²α′c), a new phase transition at a temperature , higher than T_s. By precisely identifying the semiclassical and quantum (string) gravity regimes, we find a new formula for the Kerr black hole entropy S_sem(M, J), as a function of the usual Bekenstein–Hawking entropy . For M ≫ m_Pl and J < GM²/c, is the leading term, but for high angular momentum, (nearly extremal case J = GM²/c), a gravitational phase transition operates and the whole entropy S_sem is drastically different from the Bekenstein–Hawking entropy . This new extremal black hole transition occurs at a temperature T_{sem J} = (J/ℏ)T_sem, higher than the Hawking temperature T_sem.

The color-flavor locked (CFL) phase of strangelets is investigated in a quark mass density-dependent model. Parameters are determined by stability arguments. It is concluded that three solutions to the system equations can be found, corresponding, respectively, to positively charged, negatively charged, and nearly neutral CFL strangelets. The charge to baryon number of the positively charged strangelets is smaller than the previous result, while the charge of the negatively charged strangelets is nearly proportional in magnitude to the cubic-root of the baryon number. However, the positively charged strangelets are more stable compared to the other two solutions.

Recently we considered supertwistor reformulation of the D = 4, N = 1, 2 superstring action that comprises Newman–Penrose dyad components and is classically equivalent to the Green–Schwarz one. It was shown that in the covariant κ-symmetry gauge the supertwistor representation of the string action is simplified. Here, we analyze its Hamiltonian formulation, classify the constraints on the phase-space variables, and find the covariant set of generators of the gauge symmetries. Quantum symmetries of the supertwistor representation of the string action are examined by applying the worldsheet CFT technique. Considered are various generalizations of the model from the perspective of their possible relation to the known twistor superstring models.

A planar Maxwell–Chern–Simons–Proca model endowed with a Lorentz-violating background is taken as framework to investigate the electron–electron interaction. The Dirac sector is introduced exhibiting a Yukawa and a minimal coupling with the scalar and the gauge fields, respectively. The electron–electron interaction is then exactly evaluated as the Fourier transform of the Möller scattering amplitude (carried out in the nonrelativistic limit) for the case of a purely timelike background. The interaction potential exhibits a totally screened behavior far from the origin as consequence of massive character of the physical mediators. The total interaction (scalar plus gauge potential) can always be attractive, revealing that this model may lead to the formation of electron–electron bound states.

We present a simple and general procedure for calculating the thermal radiation coming from any stationary metric. The physical picture is that the radiation arises as the quasiclassical tunneling of particles through a gravitational barrier. We study three cases in detail: the linear accelerating observer (Unruh radiation), the nonrotating black hole (Hawking radiation), and the rotating/orbiting observer (circular Unruh radiation). For the linear accelerating observer we obtain a thermal spectrum with the usual Unruh temperature. For the nonrotating black hole we obtain a thermal spectrum, but with a temperature twice that given by the original Hawking calculations. We discuss possible reasons for the discrepancies in temperatures as given by the two different methods. For the rotating/orbiting case the quasiclassical tunneling approach indicates that there is no thermal radiation. This result for the rotating/orbiting case has experimental implications for the experimental detection of this effect via the polarization of particles in storage rings.

We use group theoretic methods to obtain the extended Lie point symmetries of the quantum dynamics of a scalar particle probing the near horizon structure of a black hole. Symmetries of the classical equations of motion for a charged particle in the field of an inverse square potential and a monopole, in the presence of certain model magnetic fields and potentials are also studied. Our analysis gives the generators and Lie algebras generating the inherent symmetries.

We show that for a λϕ⁴ theory having many components, the solution with all equal components in the infrared regime is stable with respect to our expansion given by a recently devised approach to analyze strongly coupled quantum field theory. The analysis is extended to a pure Yang–Mills theory showing how, in this case, the given asymptotic series exists. In this way, many components theories in the infrared regime can be mapped to a single component scalar field theory obtaining their spectrum.

We define form-preserving transformations and Darboux transformations for time-dependent, effective mass Hamiltonians with additional linear terms. We give reality conditions for both transformations, guaranteeing the transformed potential to be real-valued. We further show that our form-preserving transformation preserves normalizability of the Schrödinger wave function. Our results generalize all former results on form-preserving transformations and Darboux transformations for the time-dependent Schrödinger equation. This paper is a sequel of Refs. 16–18.

The Casimir stress on two parallel plates in a de Sitter background corresponding to different metric signatures and cosmological constants is calculated for massless scalar fields satisfying Robin boundary conditions on the plates. Our calculation shows that for the parallel plates with false vacuum between and true vacuum outside, the total Casimir pressure leads to an attraction of the plates at very early universe.