Can Light Signals Travel Faster than c in Nontrivial Vacuua in Flat space-time? Relativistic Causality II

In this paper we show that the Scharnhorst effect (Vacuum with boundaries or a Casimir type vacuum) cannot be used to generate signals showing measurable faster-than-c speeds. Furthermore, we aim to show that the Scharnhorst effect would violate special relativity, by allowing for a variable speed of light in vacuum, unless one can specify a small invariant length scale. This invariant length scale would be agreed upon by all inertial observers. We hypothesize the approximate scale of the invariant length.Comment: 12 pages no figure

Scharnhorst effect at oblique incidence

We consider the Scharnhorst effect (anomalous photon propagation in the Casimir vacuum) at oblique incidence, calculating both photon speed and polarization states as functions of angle. The analysis is performed in the framework of nonlinear electrodynamics and we show that many features of the situation can be extracted solely on the basis of symmetry considerations. Although birefringence is common in nonlinear electrodynamics it is not universal; in particular we verify that the Casimir vacuum is not birefringent at any incidence angle. On the other hand, group velocity is typically not equal to phase velocity, though the distinction vanishes for special directions or if one is only working to second order in the fine structure constant. We obtain an ``effective metric'' that is subtly different from previous results. The disagreement is due to the way that ``polarization sums'' are implemented in the extant literature, and we demonstrate that a fully consistent polarization sum must be implemented via a bootstrap procedure using the effective metric one is attempting to define. Furthermore, in the case of birefringence, we show that the polarization sum technique is intrinsically an approximation.Comment: 11 pages double-column format, 2 figures, RevTeX 4.0 (beta 2). Final versio

Light Cone Condition for a Thermalized QED Vacuum

Within the QED effective action approach, we study the propagation of low-frequency light at finite temperature. Starting from a general effective Lagrangian for slowly varying fields whose structure is solely dictated by Lorentz covariance and gauge invariance, we derive the light cone condition for light propagating in a thermalized QED vacuum. As an application, we calculate the velocity shifts, i.e., refractive indices of the vacuum, induced by thermalized fermions to one loop. We investigate various temperature domains and also include a background magnetic field. While low-temperature effects to one loop are exponentially damped by the electron mass, there exists a maximum velocity shift of $-\delta v^2_{max}=\alpha/(3\pi)$ in the intermediate-temperature domain $T\sim m$.Comment: 9 pages, 3 figures, REVTeX, typos corrected, final version to appear in Phys. Rev.

Ekstrak Virgin Coconut Oil Sebagai Sumber Pangan Fungsional

Virgin Coconut Oil (VCO) merupakan salah satu jenis minyak nabati yang dapat bermanfaat dari aspek medis dan nutrisi karena dapat mencegah dan membantu mengobati penyakit tertentu serta dapat mempermudah proses pencernaan makanan dan penyerapan gizi. VCO dapat bertindak sebagai antioksidan dan antifotooksidan yang disebabkan oleh kandungan komponen minor (mikronutrien). Tujuan penelitian ini adalah mengekstrak komponen minor VCO menjadi produk untuk pangan fungsional yang mampu berperan sebagai antioksidan dan mengetahui peran VCO sebagai antiradikal bebas secara in vitro. Penelitian ini menggunakan metode eksperimental dengan 3 tahap yaitu: 1. Ekstraksi VCO menggunakan pelarut etanol dan metanol, 2. Pengujian penangkapan radikal bebas ekstrak VCO secara in vitro dengan metode 1,1-difenil-2-pikrilhidrazil (DPPH), 3. Identifikasi dan pengujian komponen kimia pada ekstrak VCO, identifikasi dan pengujian komponen minor pada ekstrak VCO dengan menggunakan High Performance Liquid Chromatography (HPLC). Hasil penelitian ini menunjukkan bahwa rendemen ekstrak VCO semakin tinggi dengan semakin tingginya persentase pelarut, ekstraksi dengan menggunakan etanol menghasilkan rendemen ekstrak yang lebih tinggi dibanding dengan menggunakan metanol. Aktivitas antioksidan dan kandungan total tokoferol dari ekstrak VCO semakin tinggi dengan semakin tingginya persentase pelarut yang digunakan. Salah satu senyawa tokoferol yang terdapat dalam VCO adalah -tokoferol. Berdasarkan analisa statistik menunjukkan bahwa etanol dan metanol menghasilkan sifat kimia ekstrak yang relatif sama, sehingga dapat direkomendasikan bahwa untuk mengekstraksi komponen minor dari VCO dapat menggunakan etanol karena di samping aman dari aspek kesehatan juga dapat menghasilkan rendemen ekstrak yang lebih tinggi

Light propagation in non-trivial QED vacua

Within the framework of effective action QED, we derive the light cone condition for homogeneous non-trivial QED vacua in the geometric optics approximation. Our result generalizes the ``unified formula'' suggested by Latorre, Pascual and Tarrach and allows for the calculation of velocity shifts and refractive indices for soft photons travelling through these vacua. Furthermore, we clarify the connection between the light velocity shift and the scale anomaly. This study motivates the introduction of a so-called effective action charge that characterizes the velocity modifying properties of the vacuum. Several applications are given concerning vacuum modifications caused by, e.g., strong fields, Casimir systems and high temperature.Comment: 13 pages, REVTeX, 3 figures, to appear in Phys. Rev.

Geometrical aspects of light propagation in nonlinear electrodynamics

We analyze the propagation of light in the context of nonlinear electrodynamics, as it occurs in modified QED vacua. We show that the corresponding characteristic equation can be described in terms of a modification of the effective geometry of the underlying spacetime structure. We present the general form for this effective geometry and exhibit some new consequences that result from such approach.Comment: LaTex, 11 pages, accepted for publication in Phys. Rev.

One-loop graviton corrections to Maxwell's equations

We compute the graviton induced corrections to Maxwell's equations in the one-loop and weak field approximations. The corrected equations are analogous to the classical equations in anisotropic and inhomogeneous media. We analyze in particular the corrections to the dispersion relations. When the wavelength of the electromagnetic field is much smaller than a typical length scale of the graviton two-point function, the speed of light depends on the direction of propagation and on the polarisation of the radiation. In the opposite case, the speed of light may also depend on the energy of the electromagnetic radiation. We study in detail wave propagation in two special backgrounds, flat Robertson-Walker and static, spherically symmetric spacetimes. In the case of a flat Robertson-Walker gravitational background we find that the corrected electromagnetic field equations correspond to an isotropic medium with a time-dependent effective refractive index. For a static, spherically symmetric background the graviton fluctuations induce a vacuum structure which causes birefringence in the propagation of light.Comment: 15 pages, revte