Abstract

Vacuum magnetic birefringence was predicted long time ago and is still lacking a direct experimental confirmation. Several experimental efforts are striving to reach this goal, and the sequence of results promises a success in the next few years. This measurement generally is accompanied by the search for hypothetical light particles that couple to two photons. The PVLAS experiment employs a sensitive polarimeter based on a high finesse Fabry-Perot cavity. In this paper we report on the latest experimental results of this experiment. The data are analysed taking into account the intrinsic birefringence of the dielectric mirrors of the cavity. Besides the limit on the vacuum magnetic birefringence, the measurements also allow the model-independent exclusion of new regions in the parameter space of axion-like and milli-charged particles. In particular, these last limits hold also for all types of neutrinos, resulting in a laboratory limit on their charge.

Highlights

  • IntroductionVacuum magnetic birefringence is a very small macroscopic quantum effect stemming from the 1936 Euler–Heisenberg– Weisskopf effective Lagrangian density for slowly varying electromagnetic fields [1,2,3,4] (see References [5,6]) that, to lowest order, reads: LEHW

  • Vacuum magnetic birefringence is a very small macroscopic quantum effect stemming from the 1936 Euler–Heisenberg– Weisskopf effective Lagrangian density for slowly varying electromagnetic fields [1,2,3,4] that, to lowest order, reads: LEHW = E2 c2 − B2 + Ae μ0 +7 E ·B 2 c (1) Here Ae2 α2λ3e 45μ0 mec2

  • Besides a new limit on the vacuum magnetic birefringence, the measurements allow the model-independent exclusion of new regions in the parameter space of axion-like and milli-charged particles

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Summary

Introduction

Vacuum magnetic birefringence is a very small macroscopic quantum effect stemming from the 1936 Euler–Heisenberg– Weisskopf effective Lagrangian density for slowly varying electromagnetic fields [1,2,3,4] (see References [5,6]) that, to lowest order, reads: LEHW. The relationship between the extinction coefficient κ and the absorption coefficient μ is given by μ = 4π κ/λ, where λ is the wavelength in vacuum. It can be shown [7,8,9,10,11,12] that the magnetic birefringence derived from Eq (1) is.

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The PVLAS experimental method
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The Fabry–Perot cavity as an optical path multiplier
Mirror birefringence
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Intrinsic noise of the polarimeter
Experimental setup
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Calibration
Studies of the mirrors’ wave-plates
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Vacuum measurements results and discussion
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Noise considerations
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Limits on hypothetical particles
Conclusions
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