International Journal of Modern Physics A

Dark Matter (DM) is generally assumed to be made of weakly interacting massive particles. The latter are now embedded in the Cold Dark Matter (CDM) scenario. CDM does not necessarily mean collisionless DM though. In fact, DM with quite strong interactions may still appear as perfect CDM candidates. Alternatively DM particles with weak interactions may suffer from large collisional damping effects that make them looking alike Warm (or even Hot) Dark Matter (WDM) candidates. This is expected to be relevant, in particular, if DM is lighter than a proton. Light Dark Matter particles (LDMp) were introduced as an alternative to neutralinos. They become much more interesting after one realizes that they could potentially explain the 511 keV emission line detected and mapped by INTEGRAL/SPI in the center of the galaxy. Here, we study their consequences on structure formation.

We propose a new type of cosmological model in which it is postulated that not only the temperature but also the curvature is limited by the mass scale of the Hagedorn temperature. We find that the big bang of this universe is smoothly connected to the big crunch of the previous universe through a Hagedorn universe, in which the temperature and curvature remain very close to their limiting values. In this way, we obtain the picture of a cyclic universe. By estimating the entropy gained in each big crunch and big bang, we reach the conclusion that our universe has repeated this process about forty times after it was created at the Planck scale. We also show that the model gives a scale-invariant spectrum of curvature perturbations.

Recently has been shown that the physical (mass eigenstate) color-octet technirho may not couple to two gluons. In this paper we study if this result can affect the presently accepted limits for the color-octet technirho mass obtained from the study of dijets production at the Tevatron. Our results show that no important changes are introduced on these limits.

The original Calogero and Sutherland models describe N quantum particles on the line interacting pairwise through an inverse square and an inverse sinus-square potential respectively. These models are well known to be integrable and solvable. Here we extend the Calogero and Sutherland Hamiltonians by means of new interactions which are PT-symmetric but not self-adjoint. Some of these new interactions lead to integrable PT-symmetric Hamiltonians. The algebraic properties of these interactions reveal further that they are also solvable. In addition, we consider PT-symmetric interactions which lead to new quasi-exactly-solvable deformations of the Calogero and Sutherland Hamiltonians.

Using the tadpole improved clover Wilson quark action on small, coarse and anisotropic lattices, KN scattering length in the I=1 channel is calculated within quenched approximation. The results are extrapolated towards the chiral and physical kaon mass region. Finite volume and finite lattice spacing errors are also analyzed and a result in the infinite volume and continuum limit is obtained which is compatible with the experiment and the results from Chiral Perturbation Theory.

The interactions of different particle species with the foamy space–time fluctuations expected in quantum gravity theories may not be universal, in which case different types of energetic particles may violate Lorentz invariance by varying amounts, violating the equivalence principle. We illustrate this possibility in two different models of space–time foam based on D-particle fluctuations in either flat Minkowski space or a stack of intersecting D-branes. Both models suggest that Lorentz invariance could be violated for energetic particles that do not carry conserved charges, such as photons, whereas charged particles such electrons would propagate in a Lorentz-inavariant way. The D-brane model further suggests that gluon propagation might violate Lorentz invariance, but not neutrinos. We argue that these conclusions hold at both the tree (lowest-genus) and loop (higher-genus) levels, and discuss their implications for the phenomenology of quantum gravity.

We report on the status of primordial nucleosynthesis in light of recent results on CMB anisotropies from WMAP experiment. Theoretical estimates for nuclei abundances, along with the corresponding uncertainties, are evaluated using a new numerical code, where all nuclear rates usually considered have been updated using the most recent available data. Moreover, additional processes neglected in previous calculations have been included. The combined analysis of CMB and primordial nucleosynthesis prediction for Deuterium gives an effective number of relativistic degrees of freedom in good agreement with the simplest scenario of three nondegenerate neutrinos. Our findings seem to point out possible systematics affecting ⁴He mass fraction measurements, or the effect of exotic physics, like a slightly degenerate relic neutrino background.

The presence of Odderon at high energy has been in question for quite some time. We have confronted the Odderon description to the available data especially for pp and scattering including the most recent measurements by UA4/2, E710, CDF and E811 Collaborations. The Odderon in perturbative and nonperturbative QCD has also been discussed along with some phenomenological approaches. A comparison of the Odderon description with other models has also been made for data including the measurements from cosmic ray, which corresponds to the LHC energy of 14 TeV. Our study especially focuses on the measurements at RHIC and LHC and the presence or otherwise of Odderon.

Based on the recently considered classical string configurations, in the framework of the semiclassical limit of the string/gauge theory correspondence, we describe a procedure for obtaining exact classical string solutions in general string theory backgrounds, when the string embedding coordinates depend nonlinearly on the worldsheet spatial parameter. The tensionless limit, corresponding to small 't Hooft coupling on the field theory side, is also considered. Applying the developed approach, we first reproduce some known results. Then, we find new string solutions — with two spins in AdS₅ black hole background and in AdS₅×S⁵ with two spins and up to nine independent conserved R-charges.

We consider the pp-wave limit of an exactly solvable gauged WZWN model proposed by Sfetsos and Tseytlin. The monodromy matrix is constructed for the model by adopting the methods utilized by us earlier. The pole structure of the monodromy matrix is analyzed and their properties are discussed in the context of the pp-wave limit of the gauged WZWN model.

We probed Maldacena–Nunez solution in IR with p coincident anti-D3-branes and found that these probe branes become a fuzzy NS5-brane. Doing the dual analysis, i.e. from the NS5-brane point of view with the charge of p anti-D3-brane on the world-volume of NS5-brane, we showed that to leading order this potential matches with that of p anti-D3-branes and the potential on the NS5-brane has a stable minima and have also calculated the potential, from the NS5-brane point of view, for a small fluctuation along the radial direction.