[Paper Review] Bounds on Photon Charge from Evaporation of Massive Black Holes

C. Sivaram, Kenath Arun|arXiv (Cornell University)|Mar 19, 2010

Cosmology and Gravitation Theories4 references3 citations

TL;DR

This paper derives new upper bounds on the hypothetical electric charge of photons by analyzing the Hawking radiation evaporation of massive, charged black holes, leveraging charge conservation over cosmological timescales. It shows that if photons carried a non-zero charge, it would disrupt the expected evaporation process, leading to a stringent upper limit of approximately 10^{-42} e on the photon charge, significantly tighter than previous constraints.

ABSTRACT

Photon charge has been of interest as a phenomenological testing ground for basic assumptions in fundamental physics. There have been several constraints on the photon charge based on very different considerations. In this paper we put further limits based on the well known properties of charged black holes and their subsequent evaporation by Hawking radiation and the assumption of charge conservation over this long physical process.

Motivation & Objective

• To constrain the electric charge of photons, a fundamental parameter in quantum field theory and electrodynamics.
• To investigate the implications of a non-zero photon charge on the evaporation of massive, charged black holes via Hawking radiation.
• To derive tighter bounds on photon charge by enforcing charge conservation over the long timescale of black hole evaporation.
• To provide a novel astrophysical constraint using general relativity and quantum field theory in curved spacetime.

Proposed method

• Modeling massive black holes as charged, non-rotating objects (Reissner-Nordström geometry) to study their evaporation under Hawking radiation.
• Applying the principle of charge conservation over the entire evaporation process, assuming the final state is neutral.
• Using the known spectrum of Hawking radiation to calculate the rate of energy and charge loss from the black hole.
• Deriving a bound on the photon charge by requiring that the total charge emitted during evaporation matches the initial charge of the black hole.
• Employing the relation between black hole mass, charge, and evaporation timescale to estimate the maximum allowable photon charge.
• Solving the resulting inequality to obtain an upper bound on the photon charge, assuming the photon is the only charged particle contributing to radiation.

Experimental results

Research questions

• RQ1 What upper limit on the photon charge can be derived from the requirement that charge is conserved during the Hawking evaporation of a massive black hole?
• RQ2 How does the assumption of a non-zero photon charge affect the expected evaporation dynamics of a charged black hole?
• RQ3 Can astrophysical observations of black hole evaporation be used to constrain the electromagnetic properties of the photon?
• RQ4 What is the maximum photon charge consistent with the observed or theoretically expected evaporation timescale of massive black holes?
• RQ5 How does this bound compare with other existing experimental and theoretical constraints on photon charge?

Key findings

• The paper derives an upper bound on the photon charge of approximately 10^-42 e, based on charge conservation during black hole evaporation.
• This bound is significantly tighter than previous constraints derived from laboratory experiments or atomic physics.
• The derivation assumes that photons are the only charged particles contributing to Hawking radiation, and that charge is conserved over the entire evaporation process.
• The bound is independent of the initial black hole mass, as long as it is massive enough to have a long evaporation timescale.
• The result implies that any non-zero photon charge must be extremely small, consistent with the standard model's assumption of a neutral photon.
• The method provides a novel, astrophysically motivated constraint that complements existing limits from particle physics and cosmology.