We compute the value of effective photon mass $m_\gamma$ at one-loop level in QED in the background of small ($10^{10}\,\text{g} \lesssim M \ll 10^{16}\,\text{g}$) spherically symmetric black hole in asymptotically flat spacetime. This effect is associated with the modification of electron/positron propagator in presence of event horizon. Physical manifestations of black-hole environment are compared with those of hot neutral plasma. We estimate the distance to the nearest black hole from the upper bound on $m_\gamma$ obtained in the Coulomb-law test. We also find that corrections to electron mass $m_e$ and fine structure constant $\alpha$ at one-loop level in QED are negligible in the weak gravity regime.Comment: version to be published in Nuclear Physics

We employ quantum kinetic theory to investigate local quantum physics in the background of spherically symmetric and neutral black holes formed through the gravitational collapse. For this purpose in mind, we derive and study the covariant Wigner distribution function W(x, p) near to and far away from the black-hole horizon. We find that the local density of the particle number is negative in the near-horizon region, while the entropy density is imaginary. These pose a question whether kinetic theory is applicable in the near-horizon region. We elaborate on that and propose a possible interpretation of how this result might nevertheless be self-consistently understood.

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A quantum scalar field in anti de Sitter space is considered in two coordinate systems: static and FRW-like ones. It is shown that quantum vacua corresponding to each of these coordinatizations are not unitary equivalent. A choice of a physical ground state between these vacua is discussed under different setups.