We study effects of long-lived massive particles, which decay during the big-bang nucleosynthesis (BBN) epoch, on the primordial abundances of light elements. Compared to the previous studies, (i) the reaction rates of the standard BBN reactions are updated, (ii) the most recent observational data of the light element abundances and cosmological parameters are used, (iii) the effects of the interconversion of energetic nucleons at the time of inelastic scatterings with background nuclei are considered, and (iv) the effects of the hadronic shower induced by energetic high energy anti-nucleons are included. We compare the theoretical predictions on the primordial abundances of light elements with the latest observational constraints, and derive upper bounds on the relic abundance of the decaying particle as a function of its lifetime. We also apply our analysis to unstable gravitino, the superpartner of graviton in supersymmetric theories, and obtain constraints on the reheating temperature after inflation.

We study the sensitivity of future medium baseline reactor antineutrino experiments on the neutrino mass hierarchy. By using the standard χ 2 analysis, we find that the sensitivity depends strongly on the baseline length L and the energy resolution (δE/E) 2 = a/ E/MeV 2 + b 2 , where a and b parameterize the statistical and systematic uncertainties, respectively. The optimal length is found to be L ∼ 40 − 55 km, where a slightly shorter L in the range is preferred for poorer energy resolution. The running time needed to determine the mass hierarchy also depends strongly on the energy resolution; for a 5 kton detector (with 12% weight fraction of free proton) placed at L ∼ 50 km away from a 20 GW th reactor, 3σ determination needs 14 years of running with a = 3% and b = 0.5%, which can be reduced to 5 years if a = 2% and b = 0.5%. On the other hand, the experiment can measure the mixing parameters accurately, achieving δ sin 2 2θ 12 ∼ 4 × 10 −3 , δ(m 2 2 − m 2 1 ) ∼ 0.03 × 10 −5 eV 2 , and δ|m 2 3 − m 2 1 | ∼ 0.007 × 10 −3 eV 2 , in 5 years, almost independently of the energy resolution for a < 3% and b < 1%. In order to compare our simple (∆χ 2 ) min results with those obtained by simulating many experiments, we develop an efficient method to estimate the uncertainty of (∆χ 2 ) min , and the probability for determining the right mass hierarchy by an experiment is presented as a function of the mean (∆χ 2 )

We study the effects of dark-matter annihilation during the epoch of big-bang nucleosynthesis on the primordial abundances of light elements. We improve the calculation of the light-element abundances by taking into account the effects of anti-nucleons emitted by the annihilation of dark matter and the interconversion reactions of neutron and proton at inelastic scatterings of energetic nucleons. Comparing the theoretical prediction of the primordial light-element abundances with the latest observational constraints, we derive upper bounds on the dark-matter pair-annihilation cross section. Implication to some of particle-physics models are also discussed.