Browsing by Author "Quandt, M."

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    Attractive electromagnetic Casimir stress on a spherical dielectric shell
    (Elsevier, 2013) Graham, N.; Quandt, M.; Weigel, H.
    Based on calculations involving an idealized boundary condition, it has long been assumed that the stress on a spherical conducting shell is repulsive. We use the more realistic case of a Drude dielectric to show that the stress is attractive, matching the generic behavior of Casimir forces in electromagnetism. We trace the discrepancy between these two cases to interactions between the electromagnetic quantum fluctuations and the dielectric material.
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    Quantum stabilization of a hedgehog type of cosmic string
    (Elsevier, 2017) Quandt, M.; Graham, N.; Weigel, H.
    Within a slightly simplified version of the electroweak standard model we investigate the stabilization of cosmic strings by fermion quantum fluctuations. Previous studies of quantum energies considered variants of the Nielsen–Olesen profile embedded in the electroweak gauge group and showed that configurations are favored for which the Higgs vacuum expectation value drops near the string core and the gauge field is suppressed. This work found that the strongest binding was obtained from strings that differ significantly from Nielsen–Olesen configurations, deforming essentially only the Higgs field in order to generate a strong attraction without inducing large gradients. Extending this analysis, we consider the leading quantum cor-rection to the energy per unit length of a hedgehog type string, which, in contrast to the Nielsen–Olesen configuration, contains a pseudoscalar field. To employ the spectral method we develop the scattering and bound state problems for fermions in the background of a hedgehog string. Explicit occupation of bound state levels leads to strings that carry the quantum numbers of the bound fermions. We discuss the pa-rameter space for which stable, hedgehog type cosmic strings emerge and reflect on phenomenological consequences of these findings.
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    Spectral methods for coupled channels with a mass gap
    (American Physical Society, 2018) Weigel, H.; Quandt, M.; Graham, N.
    We develop a method to compute the vacuum polarization energy for coupled scalar fields with different masses scattering off a background potential in one space dimension. As an example we consider the vacuum polarization energy of a kinklike soliton built from two real scalar fields with different mass parameters.