5 research outputs found
Axion electrodynamics: Green's functions, zero-point energy and optical activity
Starting from the theory of Axion Electrodynamics, we work out the axionic
modifications to the electromagnetic Casimir energy using the Green's function,
both when the axion field is initially assumed purely time-dependent and when
the axion field configuration is a static domain wall. For the first case it
means that the oscillating axion background is taken to resemble an axion fluid
at rest in a conventional Casimir setup with two infinite parallel conducting
plates, while in the second case we evaluate the radiation pressure acting on
an axion domain wall. We extend previous theories in order to include finite
temperatures. Various applications are discussed. 1. We review the theory of
Axion Electrodynamics and particularly the energy-momentum conservation in a
linear dielectric and magnetic material. We treat this last aspect by extending
former results by Brevik and Chaichian (2022) and Patkos (2022). 2. Adopting
the model of the oscillating axion background we discuss the axion-induced
modifications to the Casimir force between two parallel plates by using a
Green's function approach. 3. We calculate the radiation pressure acting on an
axion domain wall at finite temperature T. Our results for an oscillating axion
field and a domain wall are also useful for condensed matter physics, where
"axionic topological insulators" interact with the electromagnetic field with a
Chern-Simons interaction, like the one in Axion Electrodynamics, and there are
experimental systems analogous to time-dependent axion fields and domain walls
as the ones showed by Jiang, Q. D., \& Wilczek, F. (2019) and Fukushima et al.
(2019). 4. We compare our results, where we assume time-dependent or
space-dependent axion configurations, with the discussion of the optical
activity of Axion Electrodynamics by Sikivie (2021) and Carrol et al. (1990).Comment: To appear in the Annals of Physic
Axionic and nonaxionic electrodynamics in plane and circular geometry
Various aspects of axion electrodynamics in the presence of a homogeneous and isotropic dielectric medium are discussed. First, we consider the "antenna-like"property of a planar dielectric surface in axion electrodynamics, elaborating on the treatment given earlier on this topic by Millar et al. [J. Cosmol. Astropart. Phys. 01 (2017) 061.JCAPBP1475-751610.1088/1475-7516/2017/01/061]. We calculate the electromagnetic energy transmission coefficient for a dielectric plate, and compare with the conventional expression in ordinary electrodynamics. Second, we consider the situation where the medium exterior to the plate, assumed elastic, is "bent back"and glued together, so that we obtain a circular dielectric string in which the waves can propagate clockwise or counterclockwise. As will be shown, a stationary wave pattern is permitted by the formalism, and we show how the amplitudes for the two counterpropagating waves can be found. Third, as a special case, by omitting axions for a moment, we analyze the Casimir effect for the string, showing its similarity as well as its difference from the Casimir effect of a scalar field for a piecewise uniform string [I. Brevik and H. B. Nielsen, Phys. Rev. D 41, 1185 (1990).PRVDAQ0556-282110.1103/PhysRevD.41.1185]. Finally, including axions again we analyze the enhancement of the surface-generated electromagnetic radiation near the center of a cylindrical haloscope, where the interior region is a vacuum and the exterior region a high refractive index medium. This enhancement is caused by the curvature of the boundary, and is mathematically a consequence of the behavior of the Hankel function of the second kind for small arguments. A simple estimate shows that enhancement may be quite significant, and can therefore be of experimental interest. The presence of an absorber in the center and the possibility of adopting it to search for axions with mass in the THz region, and possibly the GHz region too, is also discussed. This proposal is suggested as an alternative to the reflector arrangement in a similar arrangement recently discussed by Liu et al. [, Phys. Rev. Lett. 128, 131801 (2022).PRLTAO0031-900710.1103/PhysRevLett.128.131801]
Axionic and nonaxionic electrodynamics in plane and circular geometry
Various aspects of axion electrodynamics in the presence of a homogeneous and isotropic dielectric medium are discussed. First, we consider the "antenna-like" property of a planar dielectric surface in axion electrodynamics, elaborating on the treatment given earlier on this topic by Millar et al. [J. Cosmol. Astropart. Phys. 01 (2017) 061.]. We calculate the electromagnetic energy transmission coefficient for a dielectric plate, and compare with the conventional expression in ordinary electrodynamics. Second, we consider the situation where the medium exterior to the plate, assumed elastic, is "bent back" and glued together, so that we obtain a circular dielectric string in which the waves can propagate clockwise or counterclockwise. As will be shown, a stationary wave pattern is permitted by the formalism, and we show how the amplitudes for the two counterpropagating waves can be found. Third, as a special case, by omitting axions for a moment, we analyze the Casimir effect for the string, showing its similarity as well as its difference from the Casimir effect of a scalar field for a piecewise uniform string [I. Brevik and H. B. Nielsen, Phys. Rev. D 41, 1185 (1990).]. Finally, including axions again we analyze the enhancement of the surface-generated electromagnetic radiation near the center of a cylindrical haloscope, where the interior region is a vacuum and the exterior region a high refractive index medium. This enhancement is caused by the curvature of the boundary, and is mathematically a consequence of the behavior of the Hankel function of the second kind for small arguments. A simple estimate shows that enhancement may be quite significant, and can therefore be of experimental interest. The presence of an absorber in the center and the possibility of adopting it to search for axions with mass in the THz region, and possibly the GHz region too, is also discussed. This proposal is suggested as an alternative to the reflector arrangement in a similar arrangement recently discussed by Liu et al. [Phys. Rev. Lett. 128, 131801 (2022).].Peer reviewe