Overcoming the Circular Problem for \gamma-ray Bursts in Cosmological Global Fitting Analysis

Due to the lack of low redshift long Gamma-Ray Bursts (GRBs), the circular problem has been a severe obstacle for using GRBs as cosmological candles. In this paper, we present a new method to deal with such a problem in MCMC global fitting analysis. Assuming that a certain type of correlations between different observables exists in a subsample of GRBs, for the parameters involved in the correlation relation, we treat them as free parameters and determine them simultaneously with cosmological parameters through MCMC analysis on GRB data together with other observational data. Then the circular problem is naturally eliminated in this procedure. We take the Ghirlanda relation as an example while keeping in mind the debate about its physical validity. Together with SNe Ia, WMAP and SDSS data, we include 27 GRBs with the reported Ghirlanda relation in our study, and perform MCMC global fitting. We consider the $\Lambda$CDM model and dynamical dark energy models. In each case, in addition to the constraints on the relevant cosmological parameters, we obtain the best fit values as well as the distributions of the correlation parameters $A$ and $C$. We find that the observational data sets other than GRBs can affect $A$ and $C$ considerably through their degeneracies with the cosmological parameters. The results on $A$ and $C$ for different cosmological models are in well agreement within $1\sigma$ range. The best fit value of $A$ in all models being analyzed is $A\sim 1.53$ with $\sigma \sim 0.08$. For $C$, we have the best value in the range of $0.94-0.98$ with $\sigma\sim 0.1$. It is also noted that the distributions of $A$ and $C$ are generally broader than the priors used in many studies in literature. (Abriged)Comment: 9 pages, 2 figures, 2 tables, Accepted for publication in Ap

Cosmological Evolution of Interacting Dark Energy Models with Mass Varying Neutrinos

In this paper we consider the cosmological implications of dark energy models with a coupled system of a dynamical scalar field (the quintessence) and the neutrinos. By detailed numerical calculations we study the various possibilities on the evolution and the fates of the universe in this class of models. Our results show that due to the interaction with quintessence, neutrinos could be dominant over the quintessence in the future universe, however would eventually decay away.Comment: One typographical error corrected, references updated and presentation improve

Vacuum Stability in Split Susy and Little Higgs Models

We study the stability of the effective higgs potential in the split supersymmetry and Little Higgs models. In particular, we study the effects of higher dimensional operators in the effective potential on the higgs mass predictions. We find that the size and sign of the higher dimensional operators can significantly change the higgs mass required to maintain vacuum stability in Split Susy models. In the Little Higgs models the effects of higher dimensional operators can be large because of a relatively lower cut-off scale. Working with a specific model we find that a contribution from the higher dimensional operator with coefficient of O(1) can destabilize the vacuum.Comment: Latex 22 pages, 3 figures. Added discussion, published versio

Cyclic Universe with Quintom matter in Loop Quantum Cosmology

In this paper, we study the possibility of model building of cyclic universe with Quintom matter in the framework of Loop Quantum Cosmology. After a general demonstration, we provide two examples, one with double-fluid and another double-scalar field, to show how such a scenario is obtained. Analytical and numerical calculations are both presented in the paper.Comment: 11 pages, 2 figure

Double Type-II Seesaw, Baryon Asymmetry and Dark Matter for Cosmic e^\pm Excesses

We construct a new realization of type-II seesaw for neutrino masses and baryon asymmetry by extending the standard model with one light and two heavy singlet scalars besides one Higgs triplet. The heavy singlets pick up small vacuum expectation values to give a suppressed trilinear coupling between the triplet and doublet Higgs bosons after the light singlet drives the spontaneous breaking of lepton number. The Higgs triplet can thus remain light and be accessible at the LHC. The lepton number conserving decays of the heavy singlets can generate a lepton asymmetry stored in the Higgs triplet to account for the matter-antimatter asymmetry in the Universe. We further introduce stable gauge bosons from a hidden sector, which obtain masses and annihilate into the Higgs triplet after spontaneous breaking of the associated non-Abelian gauge symmetry. With Breit-Wigner enhancement, the stable gauge bosons can simultaneously explain the relic density of dark matter and the cosmic positron/electron excesses.Comment: 9 pages, 4 figures, minor rewording, final PRD version (in Press

Adiabatic Gravitational Perturbation During Reheating

We study the possibilities of parametric amplification of the gravitational perturbation during reheating in single-field inflation models. Our result shows that there is no additional growth of the super-horizon modes beyond the usual predictions.Comment: Refs added; New version to appear in PR

Kinetic decoupling of neutralino dark matter

After neutralinos cease annihilating in the early Universe, they may still scatter elastically from other particles in the primordial plasma. At some point in time, however, they will eventually stop scattering. We calculate the cross sections for neutralino elastic scattering from standard-model particles to determine the time at which this kinetic decoupling occurs. We show that kinetic decoupling occurs above a temperature $T\sim$ MeV. Thereafter, neutralinos act as collisionless cold dark matter.Comment: Replaced with revised version, new references adde

Mass Hierarchy Determination Using Neutrinos from Multiple Reactors

We report the results of Monte Carlo simulations of a medium baseline reactor neutrino experiment. The difference in baselines resulting from the 1 km separations of Daya Bay and Ling Ao reactors reduces the amplitudes of 1-3 oscillations at low energies, decreasing the sensitivity to the neutrino mass hierarchy. A perpendicular detector location eliminates this effect. We simulate experiments under several mountains perpendicular to the Daya Bay/Ling Ao reactors, considering in particular the background from the TaiShan and YangJiang reactor complexes. In general the hierarchy can be determined most reliably underneath the 1000 meter mountain BaiYunZhang, which is 44.5 km from Daya Bay. If some planned reactors are not built then nearby 700 meter mountains at 47-51 km baselines gain a small advantage. Neglecting their low overhead burdens, hills near DongKeng would be the optimal locations. We use a weighted Fourier transform to avoid a spurious dependence on the high energy neutrino spectrum and find that a neural network can extract quantities which determine the hierarchy marginally better than the traditional RL + PV.Comment: 22 pages, added details on the neural network (journal version