17989564
Dark Matter -- Possible Candidates and Direct Detection
The cosmological observations coupled with theoretical calculations suggest the existence of enormous amount of unseen and unknown matter or dark matter in the universe. The evidence of their existence, the possible candidates and their possible direct detections are discussed.
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� � ,
18903505
DARK MATTER CANDIDATE IN A HEAVY HIGGS MODEL: DIRECT DETECTION RATES
We investigate direct detection rates for Dark Matter candidates arise in a SU(2)L×U(1)Y with an additional doublet Higgs proposed by Barbieri, Hall and Rychkov. We refer to this model as "Heavy Higgs Model". The Standard Model Higgs mass comes out from this model is very heavy, so there is very slim chance that there is no Higgs boson mass below 200 GeV. The additional Higgs boson develops neither any VEV due to the choice of coefficient of the scalar potential of the model nor it has any coupling with fermions due to the incorporation of a discrete parity symmetry. Thus, the neutral components of the extra doublet are stable and can be considered as probable candidate of Cold Dark Matter. We have made calculations for three different types of Dark Matter experiments, namely, 76Ge (like GENIUS), DAMA (NaI) and XENON (131Xe). Also demonstrated the annual variation of Dark Matter detection in case of all three
43103867
A Texture of neutrino mass matrix in view of recent neutrino experimental results
In view of recent neutrino experimental results such as SNO, Super-Kamiokande (SK), CHOOZ and neutrinoless double beta decay $(\beta\beta_{0\nu})$, we consider a texture of neutrino mass matrix which contains three parameters in order to explain those neutrino experimental results. We have first fitted parameters in a model independent way with solar and atmospheric neutrino mass squared differences and solar neutrino mixing angle which satisfy LMA solution. The maximal value of atmospheric neutrino mixing angle comes out naturally in the present texture. Most interestingly, fitted parameters of the neutrino mass matrix considered here also marginally satisfy recent limit on effective Majorana neutrino mass obtained from neutrinoless double beta decay experiment. We further demonstrate an explicit model which gives rise to the texture investigated by considering an $SU(2)_L\times U(1)_Y$ gauge group with two extra real scalar singlets and discrete $Z_2\times Z_3$ symmetry. Majorana neutrino masses are generated through higher dimensional operators at the scale $M$. We have estimated the scales at which singlets get VEV's and M by comparing with the best fitted results obtained in the present work.
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.
126402826
Extension of Minimal Fermionic Dark Matter Model
119713326
Nature of the scale-invariance breaking term in inelastic e-p scattering from DGS representation
Abstract Using the DGS representation and the scaling phenomena we suggest that the nature of the scale breaking term of νW 2 in inelastic e-p scattering, should be of the form G 2 (ω)M 2 Q 2 . Using Regge theory it is then predicted that G 2 ( ω ) would be a constant for large ω , and is estimated to be approximately −0.06. These predictions, in particular the constancy of the slopes for νW 2 versus 1 Q 2 plots for large ω ( ω >8), compare very well with the recent experimental data. Similar results for W 1 ( ν , Q 2 ) are also discussed.
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.
121043964
INELASTIC e--p SCATTERING DATA AND A NEW PARTON MODEL.
116971806
Problems in electromagnetic mass-difference calculations.
119967965
Effect of a transverse momentum distribution in the parton model
The parton model for the inelastic lepton-nucleon scattering is generalized to include a realistic momentum distribution of the partons. In this formalism each parton is given a component of momentum which is orthogonal in a four-vector sense to the nucleon momentum. An approximation scheme is developed to take into account the effect of this orthogonal (transverse) momentum distribution of the partons. It is found to generate an additional scale-invariant contribution to the structure function $\ensuremath{\nu}{W}_{2}(\ensuremath{\nu}, {Q}^{2})$ as well as a non-scale-invariant contribution, as is expected. The scale-invariance-breaking term is found to be a power series in $\frac{{Q}^{2}}{{\ensuremath{\nu}}^{2}}$ and vanishes as $\ensuremath{\nu}$ or ${Q}^{2}$ goes to infinity for a fixed $\ensuremath{\omega}=\frac{2M\ensuremath{\nu}}{{Q}^{2}}$. The effect of the transverse momentum distribution is explicitly displayed and discussed for a few momentum distribution functions. The data on inelastic $e\ensuremath{-}p$ scattering are then analyzed for any significant deviations from scale invariance, and it is concluded that there is evidence for such deviations. On the assumption that the systematic errors in the data are small, we make some fits which display the dependence on ${Q}^{2}$. Finally, an attempt is made to fit the data with the formalism developed in the initial part of the paper. For this purpose use is made of a model for the partons, proposed previously by the authors to explain the data in the approximation that scale invariance is satisfied. Some comments are made on the properties of partons which are necessary to fit the data and on the present status of scale-invariance breaking.