International Journal of Modern Physics A

Sterile neutrinos of keV masses are one of the most promising candidates for the warm dark matter, which could solve the small-scale problems encountered in the scenario of cold dark matter. We present a detailed study of the production of such sterile neutrinos in a supernova core, and derive stringent bounds on the active-sterile neutrino mixing angles and sterile neutrino masses based on the standard energy-loss argument.

With the historic discovery of the Higgs boson our picture of particle physics would have been complete were it not for the neutrino sector and cosmology. I briefly discuss the role of neutrino masses and mixing upon gauge coupling unification, electroweak breaking and the flavor sector. Time is ripe for new discoveries such as leptonic CP violation, charged lepton flavor violation and neutrinoless double beta decay. Neutrinos could also play a role in elucidating the nature of dark matter and cosmic inflation.

Using the fact that the neutrino mixing matrix , where U_e and U_ν result from the diagonalization of the charged lepton and neutrino mass matrices, we analyze the predictions based on the sum rules which the Dirac phase δ present in U satisfies when U_ν has a form dictated by, or associated with, discrete flavor symmetries and U_e has a "minimal" form (in terms of angles and phases it contains) that can provide the requisite corrections to U_ν, so that the reactor, atmospheric and solar neutrino mixing angles θ₁₃, θ₂₃ and θ₁₂ have values compatible with the current data.

We study the nontrivial solutions of the Quantum Chromodynamics (QCD) fermionic gap equation (FGE) including the contribution of dynamically massive gluons and the confining propagator proposed by Cornwall. Without the confining propagator, in the case of nonrunning gluon mass (m_g), we found the multivacuum solutions (replicas) reported in the literature and we were able to define limits on m_g for dynamical chiral symmetry breaking (CSB). On the other side, when considering the running in the gluon mass the vacuum replicas are absent in the limits on m_g where the chiral symmetry is broken. In the pure confining sector, the multivacuum states are always absent so it is said that only one stable solution for the gap equation is found as claimed in previous analysis using different approaches. Finally, in the case of the complete gap equation i.e. with both contributions, the vacuum replicas are also absent in both cases; with constant and with running gluon mass.

A geometric torsion dynamics leading to an effective curvature in a second-order formalism on a D₄-brane is revisited with a renewed interest. We obtain two effective AdS₄ brane geometries on a vacuum created pair of -brane. One of them is shown to describe an AdS Schwarzschild spinning black hole and the other is shown to describe a spinning black hole bound state. It is argued that a D-instanton in a vacuum created anti-D₃-brane within a pair may describe a quintessence. It may seem to incorporate a varying vacuum energy density in a brane universe. We consider the effective curvature scalar on S¹ × S¹ to analyze torsionless geometries on a vacuum created pair of -brane. The emergent AdS₃ brane is shown to describe a Schwarzschild and a Reissner–Nordstrom (RN) geometries in the presence of extra dimension(s).

It is suggested that the Tunguska event in June 1908 was due to a cm-large ball of a condensate of bound states of 6 top and 6 antitop quarks containing highly compressed ordinary matter. Such balls are supposed to make up the dark matter as we earlier proposed. The expected rate of impact of this kind of dark matter ball with the earth seems to crudely match a time scale of 200 years between the impacts. The main explosion of the Tunguska event is explained in our picture as material coming out from deep within the earth, where it has been heated and compressed by the ball penetrating to a depth of several thousand km. Thus the effect has some similarity with volcanic activity as suggested by Kundt. We discuss the possible identification of kimberlite pipes with earlier Tunguska-like events. A discussion of how the dark matter balls may have formed in the early universe is also given.

We study the collisional aspects of jet quenching in a high-energy nuclear collision, especially in the final state pion gas. The jet has a large energy, and acquires momentum transverse to its axis more effectively by multiple soft collisions than by few hard scatterings (as known from analogous systems such as J/ψ production at Hera). Such regime of large E and small momentum transfer corresponds to Regge kinematics and is characteristically dominated by the pomeron. From this insight we estimate the jet quenching parameter in the hadron medium (largely a pion gas) at the end of the collision, which is naturally small and increases with temperature in line with the gas density and compare it to the jet quenching parameter obtained within the quark–gluon plasma (QGP) phase in widely known perturbative approximations. The physics in the quark–gluon plasma/liquid phase is less obvious, and here we revisit a couple of simple estimates that suggest indeed that the pomeron-mediated interactions are very relevant and should be included in analysis of the jet quenching parameter. Finally, since the occasional hard collisions produce features characteristic of a Lèvy flight in the plane perpendicular to the jet axis, we suggest one- and two-particle q_⊥ correlations as interesting experimental probes sensitive to the nature (softness versus hardness) of the interactions of a jet inside the QGP.

We discuss various space–time metrics which are compatible with Einstein's equations and a previously suggested cosmology with a finite total mass.¹ In this alternative cosmology, the matter density was postulated to be a spatial delta function at the time of the big bang thereafter diffusing outward with constant total mass. This proposal explores a departure from standard assumptions that the big bang occurred everywhere at once or was just one of an infinite number of previous and later transitions.

We study general models for holographic superconductors with higher correction terms of the scalar field in the four-dimensional AdS black hole background including the matter fields' backreaction on the metric. We explore the effects of the model parameters on the scalar condensation and find that different values of model parameters can determine the order of phase transitions. Moreover, we find that the higher correction terms provide richer physics in the phase transition diagram.

Using the properties of the partition function for a Yang–Mills theory we compute simple relations among the renormalization constants. In the particular case of the background gauge field method we obtain that the all orders beta function for the gauge coupling constant contains only the first two orders coefficients different than zero and thus corresponds to the 't Hooft scheme.