Modern Physics Letters A

Beyond spatial anisotropy and polarization, a third type of structure in the Cosmic Microwave Background radiation, that of deviations in the overall absolute intensity versus frequency spectrum from a blackbody form, encodes additional important cosmological and astrophysical information, and remains inconclusively studied. This article discusses the ARCADE 2 project, the current balloon-based experimental effort to measure the absolute radiometric temperature of the CMB and Galactic microwave emission in the range from 3 to 90 GHz.

If the Standard Model is correct, and fundamental fermions exist only in the three generations, then the CKM matrix should be unitary. However, there remains a question over a deviation from unitarity from the value of the neutron lifetime. We discuss a simple space-based experiment that, at an orbit height of 500 km above Earth, would measure the kinetic-energy, solid-angle, flux spectrum of gravitationally bound neutrons (kinetic energy K< 0.606 eV at this altitude). The difference between the energy spectrum of neutrons that come up from the Earth's atmosphere and that of the undecayed neutrons that return back down to the Earth would yield a measurement of the neutron lifetime. This measurement would be free of the systematics of laboratory experiments. A package of mass < 25 kg could provide a 10^-3 precision in two years.

We consider the gravitational collapse of a spherically symmetric ball of dust in the general relativistic weak gravity regime. The velocity of the matter as viewed by external observers is compared to the velocity gauged by local observers. While the comparison in the case of very strong gravity is seen to follow the pattern familiar to the studies of test particles falling towards a concentrated mass, the case of weak gravity is very different. The velocity of the dust that is witnessed by external observers is derived for the critically open case and is seen to differ markedly from the expectations based upon Newtonian gravity theory. Viewed as an idealized model for a cluster of galaxies, we find that with the general relativistic velocity expression, the higher-than-expected constituent velocities observed can be readily correlated with the solely baryonic measure of the mass, obviating the need to introduce extraneous dark matter. It would be particularly valuable if a laboratory or space-based realization of a spherical collapse could be implemented to compare the velocity expression as a new test of general relativity.

New Galilei quantum groups dual to the Hopf algebras proposed in Ref. 1 are obtained by the nonrelativistic contraction procedures. The corresponding Lie-algebraic and quadratic quantum spacetimes are identified with the translation sectors of considered algebras.

We have introduced the Cornwall–Jackiw–Tomboulis (CJT) resummation scheme in studying nuclear matter. Based on the CJT formalism and using Walecka model, we have derived a set of coupled Dyson equations of nucleons and mesons. Neglecting the medium effects of the mesons, the usual mean field theory (MFT) results can be obtained. The beyond MFT calculations have been performed by thermodynamic consistently determining the meson effective masses and solving the coupled gap equations for nucleons and mesons together. The numerical results for the nucleon and meson effective masses at finite temperature and chemical potential in nuclear matter are discussed.

We study finite temperature phase transition of neutral scalar field on a fuzzy sphere using Monte Carlo simulations. We work with the zero mode in the temporal directions, while the effects of the higher modes are taken care by the temperature dependence of r. In the numerical calculations we use "pseudo-heatbath" method which reduces the auto-correlation considerably. Our results agree with the conventional calculations. We report some new results which show the presence of meta-stable states, first order symmetry breaking transition and existence of multiple triple points in the phase diagram..

In this paper using the first Casimir operator of de Sitter group we obtain the field equations for spin-0 and spin-1/2 fields. After finding the exact solutions, we calculate the Bogoliubov coefficients and the particle creation rate for scalar and Dirac particles. Three series of inequivalent representations are distinguished for de Sitter group: the principal, complementary and discrete series. It is shown that only for principal series massive particles are produced. The thermal particle creation rate is compared with the previous results and it is shown that the results are the same.