Second Order Corrections to QED Coupling at Low Temperature

We calculate the second order corrections to vacuum polarization tensor of photons at low temperatures, i.e; T $\le 10^{10}$ K ($T << m_e$). The thermal contributions to the QED coupling constant are evaluated at temperatures below the electron mass that is $T< m_e$ . Renormalization of QED at these temperatures has explicitly been checked. The electromagnetic properties of such a thermal medium are modified. Parameters like electric permittivity and magnetic permeability of such a medium are no more constant and become functions of temperature.Comment: 8 latex pages and 1 figure (to appear in IJMP

Magnetic Dipole Moment of Neutrino

We recalculate the magnetic moment of neutrinos in a hot and dense medium. The magnetic dipole moment of neutrinos is modified at high temperature and chemical potential. We show that the magnetic dipole moment of electron neutrino does not get a significant contribution from thermal background to meet the cosmological bound. However, chemical potential contribution to the magnetic moment is non-ignorable even when chemical potential is an order of magnitude greater than the electron mass. It is demonstrated that this effect is more significant in the models with an extended Higgs sector through neutrino mixing

Second Order Corrections to the Magnetic Moment of Electron at Finite Temperature

Magnetic moment of electron at finite temperature is directly related to the modified electron mass in the background heat bath. Magnetic moment of electron gets modified when it couples with the magnetic field at finite temperature through its temperature dependent physical mass. We show that the magnetic moment of electron becomes a complicated function of temperature and even change its temperature dependent behavior around the energies for primordial nucleosynthesis. We calculate the self-mass induced thermal contributions to the magnetic moment of electron, up to the two loop level, for temperatures valid around the era of primordial nucleosynthesis. A comparison of thermal behavior of the magnetic moment is also quantitatively studied in detail, around the temperatures below and above nucleosynthesis temperature range