Modern Physics Letters A

This is a brief review of Refs. 1 and 2. We study the dynamics of D0-brane falling into the Lorentzian two-dimensional black hole (2D BH), typically arising in the near-horizon limit of non-extremal NS5-brane background, by the methods of conformal field theory. We propose the exact boundary state describing the infalling D0-brane by carefully carrying out the Wick rotation from the known D1-brane solution. We evaluate the closed string radiation from the infalling brane. A thermal-like behavior at the Hawking temperature is observed in the outgoing radiation. On the other hand, it is remarkable to find the incoming radiation absorbed by the black hole effectively showing the Hagedorn-like behavior with precise α′-correction. We confirm this feature by exactly analyzing the imaginary part of cylinder amplitudes, as well as the saddle point approximation. The radiation rate curiously depends on the level k of SL(2)/U(1) supercoset, suggesting the "black hole/string phase transition" at k = 1 (k = 3 for the bosonic coset) discussed recently.

In an improved application of the tetrahedral symmetry A₄ first introduced by Ma and Rajasekaran, supplemented by the discrete symmetry Z₃ as well as supersymmetry, a two-parameter form of the neutrino mass matrix is derived which exhibits the tribimaximal mixing of Harrison, Perkins and Scott. This form is the same as the one obtained previously by Altarelli and Feruglio, and the inverse of that obtained by Babu and He. If only A₄ is used, then corrections appear, making tan² θ₁₂ different from 0.5, without changing significantly sin²2θ₂₃ from one or θ₁₃ from zero.

The loop variable technique (for open strings in flat space) is a gauge-invariant generalization of the renormalization group method for obtaining equations of motion. Unlike the beta functions, which are only proportional to the equations of motion, here it gives the full equation of motion. In an earlier paper, a technique was described for adapting this method to open strings in gravitational backgrounds. However, unlike the flat space case, these equations cannot be derived from an action and are therefore not complete. This is because there are ambiguities in the method that involve curvature couplings that cannot be fixed by appealing to gauge invariance alone but need a more complete treatment of the closed string background. An indirect method to resolve these ambiguities is to require symmetricity of the second derivatives of the action. In general this will involve modifying the equations by terms with arbitrarily high powers of curvature tensors. This is illustrated for the massive spin-two field. It is shown that in the special case of an AdS or dS background, the exact action can easily be determined in this way.

It is shown that background fields of a topological character usually introduced as such in compactified string theories correspond to quantum degrees of freedom which parametrise the freedom in choosing a representation of the zero-mode quantum algebra in the presence of nontrivial topology.

The Hanbury-Brown and Twiss (HBT) effects predict a Bose–Einstein enhancement of the two-particle momentum correlations of identical bosons at small relative momentum. However, the parallel momentum correlations between identical fermions are less argued. The momentum correlations can be altered by many factors, among which the spin interaction effects are discussed in this paper. It is found that the spin interaction plays an important role on the momentum correlations of identical fermions. For spin triplet state, a full Fermi–Dirac suppression represents as expected. On the contrary, a fake Bose–Einstein enhancement shows up for spin singlet state. The measured momentum correlations of fermions could hence provide some hints of spin interactions between them if all other factors such as Coulomb interactions were removed. Spin interactions make it more complicated to extract physical information from momentum correlations between fermions.

The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in X-ray binaries. We present the set of characteristics frequencies associated with accretion disk around the rotating and non-rotating black holes for one particle case. These persistent frequencies are results of the rotating pattern in an accretion disk. We compare the frequency's from two different numerical results for fluid flow around the non-rotating black hole with one particle case. The numerical results are taken from Refs. 1 and 2 using fully general relativistic hydrodynamical code with non-selfgravitating disk. While the first numerical result has a relativistic tori around the black hole, the second one includes one-armed spiral shock wave produced from star-disk interaction. Some physical modes presented in the QPOs can be excited in numerical simulation of relativistic tori and spiral waves on the accretion disk. The results of these different dynamical structures on the accretion disk responsible for QPOs are discussed in detail.