Abelian Gauge Extension of Standard Model: Dark Matter and Radiative Neutrino Mass

We study a simple extension of Standard Model where the gauge group is extended by an additional $U(1)_X$ gauge symmetry. Neutrino mass arise both at tree level as well as radiatively by the anomaly free addition of one singlet fermion $N_R$ and two triplet fermions $\Sigma_{1R}, \Sigma_{2R}$ with suitable Higgs scalars. The spontaneous gauge symmetry breaking is achieved in such a way which results in a residual $Z_2$ symmetry and hence providing a stable cold dark matter candidate. We study the possible dark matter candidates in this model by incorporating the constraints from cosmology as well as direct detection experiments. We discuss both low and high mass (from GeV to the TeV scale) regimes of fermionic and scalar dark matter candidates in the model. We show that scalar dark matter relic density, although not significantly affected by the presence or absence of annihilation into $U(1)_X$ gauge boson pairs, is however affected by choice of $U(1)_X$ gauge charges. We discuss the neutrino mass phenomenology and its compatibility with the allowed dark matter mass ranges and also comment on the implications of the model on Higgs signatures at colliders including those related to fourth fermion generation.Comment: 20 pages, 6 figures, figures redrawn and conclusion unchanged, Journal versio

Neutrino and astroparticle physics : Working group report

The contributions made to the Working Group activities on neutrino and astroparticle physics are summarised in this article. The topics discussed were leptogenesis in Left-Right symmetric model, inflationary models in Raman-Sundrum scenarios, ultra high energy cosmic rays and neutrino oscillations in 4 flavour and decaying neutrino models.Comment: 11 pages; arXiv copy of contribution to WHEPP-6 proceeding

Heat capacity and magnetoresistance in Dy(Co,Si)2 compounds

Magnetocaloric effect and magnetoresistance have been studied in Dy(Co1-xSix)2 [x=0, 0.075 and 0.15] compounds. Magnetocaloric effect has been calculated in terms of adiabatic temperatue change (Delta Tad) as well as isothermal magnetic entropy change (Delta SM) using the heat capacity data. The maximum values of DeltaSM and DeltaTad for DyCo2 are found to be 11.4 JKg-1K-1 and 5.4 K, respectively. Both DSM and DTad decrease with Si concentration, reaching a value of 5.4 JKg-1K-1 and 3 K, respectively for x=0.15. The maximum magnetoresistance is found to about 32% in DyCo2, which decreases with increase in Si. These variations are explained on the basis of itinerant electron metamagnetism occurring in these compounds.Comment: Total 8 pages of text and figure

Effective SO Superpotential for N=1 Theory with N_f Fundamental Matter

Motivated by the duality conjecture of Dijkgraaf and Vafa between supersymmetric gauge theories and matrix models, we derive the effective superpotential of N=1 supersymmetric gauge theory with gauge group SO(N_c) and arbitrary tree level polynomial superpotential of one chiral superfield in the adjoint representation and N_f fundamental matter multiplets. For a special point in the classical vacuum where the gauge group is unbroken, we show that the effective superpotential matches with that obtained from the geometric engineering approach.Comment: LaTeX, 1+19 pages, To appear in Nucl.Phys.

Limit laws for k-coverage of paths by a Markov-Poisson-Boolean model

Let P := {X_i,i >= 1} be a stationary Poisson point process in R^d, {C_i,i >= 1} be a sequence of i.i.d. random sets in R^d, and {Y_i^t; t \geq 0, i >= 1} be i.i.d. {0,1}-valued continuous time stationary Markov chains. We define the Markov-Poisson-Boolean model C_t := {Y_i^t(X_i + C_i), i >= 1}. C_t represents the coverage process at time t. We first obtain limit laws for k-coverage of an area at an arbitrary instant. We then obtain the limit laws for the k-coverage seen by a particle as it moves along a one-dimensional path.Comment: 1 figure. 24 Pages. Accepted at Stochastic Models. Theorems 6 and 7 corrected. Theorem 9 and Appendix adde

Electronic structure of spin 1/2 Heisenberg antiferromagnetic systems: Ba_2Cu(PO_4)_2 and Sr_2Cu(PO_4)_2

We have employed first principles calculations to study the electronic structure and magnetic properties of the low-dimensional phosphates, Ba2Cu(PO4)2 and Sr2Cu(PO4)2. Using the self-consistent tight-binding lin- earized muffin-tin orbital method and the Nth order muffin-tin orbital method, we have calculated the various intrachain as well as the interchain hopping parameters between the magnetic ions Cu2+ for both the com- pounds. We find that the nearest-neighbor intrachain hopping t is the dominant interaction suggesting the compounds to be indeed one dimensional. Our analysis of the band dispersion, orbital projected band struc- tures, and the hopping parameters confirms that the Cu2+-Cu2+ super-super exchange interaction takes place along the crystallographic b direction mediated by O-P-O. We have also analyzed in detail the origin of short-range exchange interaction for these systems. Our ab initio estimate of the ratio of the exchange inter- action of Sr2Cu(PO4)2 to that of Ba2Cu(PO4)2 compares excellently with available experimental results.Comment: 6 pages, 4 figure

Spontaneously broken parity and consistent cosmology with transitory domain walls

Domain wall structure which may form in theories with spontaneously broken parity is generically in conflict with standard cosmology. It has been argued that Planck scale suppressed effects can be sufficient for removing such domain walls. We study this possibility for three specific evolution scenarios for the domain walls, with evolution during radiation dominated era, during matter dominated era, and that accompanied by weak inflation. We determine the operators permitted by the supergravity formalism and find that the field content introduced to achieve desired spontaneous parity breaking makes possible Planck scale suppressed terms which can potentially remove the domain walls safely. However, the parity breaking scale, equivalently the majorana mass scale $M_R$ of the right handed neutrino, does get constrained in some of the cases, notably for the matter dominated evolution case which would be generic to string theory inspired models giving rise to moduli fields. One left-right symmetric model with only triplets and bidoublets is found to be more constrainted than another admitting a gauge singlet

Probing Lorentz Invariance at EeV Energy

Pierre Auger experiment has detected at least a couple of ray events above energy 60 EeV from the direction of the radio-galaxy Centaurus A. Assuming those events are from Centaurus A, we have calculated the number of neutral cosmic ray events from this source for small values of the degree of violation in Lorentz invariance. Our results show that a comparison of our calculated numbers of events with the observed number of events at EeV energy from the direction of the source can probe extremely low value of the degree of this violation.Comment: 8 pages,4 figure

Indication of transverse radial flow in high-multiplicity proton-proton collisions at the Large Hadron Collider

We analyze the measured spectra of $\pi^\pm$, $K^\pm$, $p$($\bar p$) in $pp$ collisions at $\sqrt {s}$ = 0.9, 2.76 and 7 TeV, in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in $pp$ collisions. The dependency of the blast-wave parameters on average charged particle multiplicity of event sample or the `centrality' of collisions has been studied and compared with results of similar analysis in nucleus-nucleus ($AA$) and proton-nucleus ($pA$) collisions. We analyze the spectra of $K_{s}^0$, $\Lambda$($\bar \Lambda$) and $\Xi^-$ also to see the dependence of blast-wave description on the species of produced particles. Within the framework of the blast-wave model, the study reveals indication of collective behavior for high-multiplicity events in $pp$ collisions at LHC. Strong transverse radial flow in high multiplicity $pp$ collisions and its comparison with that in $pA$ and $AA$ collisions match with predictions from a very recent theoretical work [Shuryak and Zahed 2013 arXiv:1301.4470] that addresses the conditions for applicability of hydrodynamics in $pp$ and $pA$ collisions.Comment: 14 pages 8 figure

Role of dual nuclear baths on spin blockade leakage current bistabilities

Spin-blockaded electronic transport across a double quantum dot (DQD) system represents an important advancement in the area of spin-based quantum information. The basic mechanism underlying the blockade is the formation of a blocking triplet state. The bistability of the leakage current as a function of the applied magnetic field in this regime is believed to arise from the effect of nuclear Overhauser fields on spin-flip transitions between the blocking triplet and the conducting singlet states. The objective of this paper is to present the nuances of considering a two bath model on the experimentally observed current bistability by employing a self consistent simulation of the nuclear spin dynamics coupled with the electronic transport of the DQD set up. In doing so, we first discuss the important subtleties involved in the microscopic derivation of the hyperfine mediated spin flip rates. We then give insights as to how the differences between the two nuclear baths and the resulting difference Overhauser field affect the two-electron states of the DQD, and their connection with the experimentally observed current hysteresis curve.Comment: 9 pages, 5 figure