118595488
Generalizing thawing dark energy models: the standard vis-à-vis model independent diagnostics
We propose a two parameter generalization for the dark energy equation of state (EOS) wX for thawing dark energy models which includes PNGB, CPL and Algebraic thawing models as limiting cases and confront our model with the latest observational data namely SNe Ia, OHD, CMB, BOSS data. Our analysis reveals that the phantom type of thawing dark energy is favoured upto 2� confidence level. These results also show that thawing dark e nergy EOS is not unique from observational point of view. Though different thawing dark energy models are not distinguishable from each other from best-fit values (upto 2� C.L.s) of matter density parameter ( 0) and hubble parameter (H0) at present epoch, best-fit plots of linear growth of matter perturbation (f ) and average deceleration parameter (qav); the difference indeed reflects in best-fit variations of thawing dark energy EOS, model-independent geometrical diagnostics like the statefinder pair {r, s} and Om3 parameter. We are thus led to the conclusion that unlike the standard observables ( 0, H0, f , qav), the model-independent pa� � ,
15935653
Effect of flavour oscillations on the detection of supernova neutrinos
Neutrinos and antineutrinos of all three flavours are emitted during the post-bounce phase of a core-collapse supernova with having average energies more than that of They can be detected by the new earthbound detectors like SNO and Super-Kamiokande which are sensitive to neutrinos of all three flavours. In this letter we consider the effect of flavour oscillations on the neutrino flux and their expected number of events at the detector. We do a three-generation analysis and for the mass and mixing schemes we first consider the threefold maximal mixing model consistent with the solar and the atmospheric neutrino data and next a scenario with one m2~10-11 eV2 (solar range) and the other m2~10-18 eV2, for which the oscillation length is of the order of the supernova distance. In both these scenarios there are no matter effects in the resultant neutrino spectrum and one is concerned with vacuum oscillations. We find that though neutrino oscillations result in a depletion in the number of e and coming from the supernova, the actual signals at the detectors are appreciable enhanced as the e and energy spectra become harder.
2568474
Late-time acceleration in a slow-moving Galileon field
�� 2M2 � ;� � ;� respects the Galileon symmetry in curved spacetime. We carry out detailed investigations of the underlying dynamics of this Lagrangian with an Einstein-Hilbert term and a potential. We demonstrate that the model can give rise to a viable ghost-free late-time acceleration of the universe. Furthermore, we study the cosmological perturbation of the model and see that the model gives different big bang nucleosynthesis constraints at early times. We also carry out the observational analysis of the model and use observational data from growth, type Ia supernovae data, baryon acoustic oscillations, and the cosmic microwave background to constrain the parameters of the theory. From cosmological observations (1-4) it is evident that our Universe is currently undergoing an accelerated ex- pansion. The theoretical understanding of the nature of cosmic repulsion is a challenge for the cosmologist and the particle physicist today. A variety of approaches have been studied to address this problem, but to date there is still no definite answer. According to the standard ap- proach, the late-time acceleration can be accounted for by supplementing the energy-momentum tensor by an exotic fluid component with large negative pressure dubbed dark energy (5-12), which constitutes about three quarters of the total cosmic budget of the Universe (13). The simplest candidate for dark energy which is consistent with the observations is provided by a cosmological con- stant � . However, there are various serious theoretical problems associated to it, namely, the fine-tuning and the coincidence problems. An interesting alternative to a cosmological constant is provided by the scalar fields. The cosmological dynamics of a variety of scalar field models has been studied in the literature (7). Though these models do not address the cosmological constant problem, they can give late-time cosmic acceleration and can also provide a viable cosmo- logical dynamics at early epochs. Scalar field models with generic features like the trackers are capable of alleviating the fine-tuning and coincidence problems. At present, these scalar field models are absolutely consistent with the observations but, at the same time, a large number of these models are also permitted. One must therefore rely on future data which should allow one to narrow down the class of permissible scalar field dark energy models.
118940895
"Bimaximal + Democratic"type neutrino mass matrix in view of quark-lepton complementarity
We demonstrate that `Bimaximal + Democratic' type neutrino mass matrix can accommodate the deviation of $\theta_\odot$ from its maximal value which referred in the literature as `quark-lepton complementarity' along with the other present day neutrino experimental results, namely, atmospheric, CHOOZ, neutrinoless double beta decay ($\beta\beta_{0\nu}$) and result obtained from WMAP experiment. We define a function $\chi_p$ in terms of solar and atmospheric neutrino mass squared differences and solar neutrino mixing angle (obtained from different experiments and our proposed texture). The masses and mixing angles are expressed in terms of three parameters in our proposed texture. The allowed region of the texture parameters is obtained through minimization of the above function. The proposed texture crucially depends on the value of the experimental results of $\beta\beta_{0\nu}$ experiment among all other above mentioned experiments. If, in future, $\beta\beta_{0\nu}$ experiments, namely, MOON, EXO, GENIUS shift the lower bound on $$ at the higher side by one order, the present texture will be ruled out.
118455395
Quintom scalar field : Varying dark energy equation of state obtained from recent SNe Ia, BAO and OHD data
From the analysis of Supernova Ia data alongwith Observational Hubble Data (OHD) and Baryon Acoustic Oscillation (BAO) data, we attempt to find out the nature of a scalar potential that may be responsible for the Dark Energy of the universe. We demonstrate that in order to explain the varying dark energy equation of state ($\omega_X(z)$) as obtained in a model independent way from the analyses of observational data, we need to invoke a quintom scalar field having a "quintessence" part for $\omega_X(z) > -1$ and a "phantom" part for $\omega_X(z) < -1$. We consider a Gaussian type potential for these scalar fields and compare the dark energy equation of state derived from such potential with the one computed from the data analysis.
11939062
Unparticle decay of neutrinos and it's effect on ultra high energy neutrinos
The unparticle is proposed by Georgi as a conceptual new physics beyond the standard model to describe the low energy sector of a nontrivial scale invariant sector of an effective theory. We consider the neutrino decay in unparticle scenario and investigate the effect of such decay for the case of ultra high energy neutrinos from GRB. The effect on the detection yield of these neutrinos are also probed for a kilometer scale ice-Cerenkov detector.
120089980
ELECTROMAGNETIC MASS DIFFERENCES.
Abstract In Cottingham's approach to electromagnetic masses ( δm ) one encounters the problem of unknown subtractions in the fixed mass dispersion relations for the virtual Compton scattering amplitude. We avoid this problem and express δm in terms of measurable quantities, assuming knowledge of light-cone singularities of the electro-magnetic current commutator.
120652883
Model for the leading light-cone singularity of the current commutator
119974277
Inelastic-Compton-Scattering Inequalities in the Quark-Parton Model