[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Direct nuclear reactions

The treatment of first-order phase transitions for standard grand unified theories is shown to break down for models with radiatively induced spontaneous symmetry breaking. It is argued that proper analysis of these transitions which would take place in the early history of the universe can lead to an explanation of the cosmological homogeneity, flatness, and monopole puzzles.

Cosmology for Grand Unified Theories with Radiatively Induced Symmetry Breaking

Nuclear collisions can compress nuclear matter to densities achieved within neutron stars and within core-collapse supernovae. These dense states of matter exist momentarily before expanding. We analyzed the flow of matter to extract pressures in excess of 1034 pascals, the highest recorded under laboratory-controlled conditions. Using these analyses, we rule out strongly repulsive nuclear equations of state from relativistic mean field theory and weakly repulsive equations of state with phase transitions at densities less than three times that of stable nuclei, but not equations of state softened at higher densities because of a transformation to quark matter.

Determination of the Equation of State of Dense Matter

We investigate possible interactions between neutrinos and massive scalar bosons via g(phi)(nu) over bar nu phi (or massive vector bosons via g(V)(nu) over bar gamma(mu)nu V-mu) and explore the all ...

Observational constraints on secret neutrino interactions from big bang nucleosynthesis

The relativistic Feynman-Metropolis-Teller treatment of compressed atoms is extended to treat magnetized matter. Each atomic configuration is confined by a Wigner-Seitz cell and is characterized by a positive electron Fermi energy which varies insignificantly with the magnetic field. In the relativistic treatment the limiting configuration is reached when the Wigner-Seitz cell radius equals the radius of the nucleus with a maximum value of the electron Fermi energy which can not be attained in presence of magnetic field due to the effect of Landau quantization of electrons within the Wigner-Seitz cell. This treatment is implemented to develop the Equation of State for magnetized White Dwarf stars in presence of Coulomb screening. The mass-radius relations for magnetized White Dwarfs are obtained by solving the general relativistic hydrostatic equilibrium equations using Schwarzschild metric description suitable for non rotating and slowly rotating stars. The explicit effects of the magnetic energy density and pressure contributed by a density-dependent magnetic field are included to find the stable configurations of magnetized Super-Chandrasekhar White Dwarfs.

Relativistic Thomas-Fermi equation of state for magnetized white dwarfs

In this work, we study the $r$-mode instability windows and the gravitational wave signatures of neutron stars in the slow rotation approximation using the equation of state obtained from the density-dependent M3Y effective interaction. We consider the neutron star matter to be $\ensuremath{\beta}$-equilibrated neutron-proton-electron matter at the core with a rigid crust. The fiducial gravitational and viscous timescales, the critical frequencies, the time evolutions of the frequencies, and the rates of frequency change are calculated for a range of neutron star masses. We show that the young and hot rotating neutron stars lie in the $r$-mode instability region. We also emphasize that if the dominant dissipative mechanism of the $r$ mode is the shear viscosity along the boundary layer of the crust-core interface, then the neutron stars with low $L$ value lie in the $r$-mode instability region and hence emit gravitational radiation.

Gravitational waves from isolated neutron stars: Mass dependence of r -mode instability

We study the properties of the neutron-nucleus total and reaction cross sections for several nuclei. We have applied an analytical model, the nuclear Ramsauer model, justified it from the nuclear reaction theory approach, and extracted the values of 12 parameters used in the model. The given parametrization has an advantage as phenomenological optical model potentials are limited up to 150-200 MeV. The present model provides good estimates of the total cross sections for several nuclei particularly at high energies.

Cross sections of neutron-induced reactions

Prediction of the primordial abundances of elements in the big-bang nucleosynthesis (BBN) is one of the three strong evidences for the big bang model. Precise knowledge of the baryon-to-photon ratio of the Universe from observations of the anisotropies of cosmic microwave background radiation has made the Standard BBN a parameter-free theory. Although, there is a good agreement over a range of nine orders of magnitude between abundances of light elements deduced from observations and calculated in primordial nucleosynthesis, there remains a yet-unexplained discrepancy of 7Li abundance higher by a factor of ~3 when calculated theoretically. The primordial abundances depend on the astrophysical nuclear reaction rates and on three additional parameters, the number of light neutrino flavors, the neutron lifetime and the baryon-to-photon ratio in the Universe. The effect of the modification of thirty-five reaction rates on light element abundance yields in BBN was investigated earlier by us. In the present work we have incorporated the most recent values of neutron lifetime and the baryon-to-photon ratio and further modified 3He(4He, γ)7Be reaction rate which is used directly for estimating the formation of 7Li as a result of β+ decay as well as the reaction rates for t(4He,γ)7Li and d(4He,γ)6Li. We find that these modifications reduce the theoretically calculated abundance of 7Li by ~12%.

Joydev Lahiri

Papers

Relativistic Thomas-Fermi equation of state for magnetized white dwarfs

Gravitational waves from isolated neutron stars: Mass dependence of r -mode instability

Cross sections of neutron-induced reactions

Big-Bang Nucleosynthesis and Primordial Lithium Abundance Problem

Theoretical estimates of cross sections for neutron–nucleus collisions