Black Holes Rule Out Heavy Tachyons

TL;DR

This paper uses black hole observations and Hawking radiation calculations to set upper limits on the mass of hypothetical tachyon particles, ruling out their existence at certain high energy scales.

Contribution

It provides the first direct observational constraints on heavy tachyons by analyzing their gravitational effects via black hole evaporation.

Findings

Black hole lifetime is significantly affected by heavy tachyons.

Black holes of a few solar masses with long lifetimes exclude tachyons heavier than 3×10^9 GeV.

Tachyons associated with unification or quantum gravity scales are ruled out.

Abstract

We present direct observational constraints on tachyons; particles with group velocity greater than $c$ in vacuum in a Lorentz invariant theory. Since tachyons may have no direct couplings to Standard Model particles, the most robust and model independent constraints come from gravitational effects, especially black holes. We compute the Hawking radiation of tachyons from black holes, finding it to be significantly enhanced in the presence of heavy tachyons. For a black hole of mass $M$ and tachyons of mass $m$ with $g$ degrees of freedom, the black hole lifetime is found to be $t_{bh} \approx 192 \pi \hbar M/(g c^2 m^2)$ (or doubled for fermions). This implies that the observation of black holes of a few solar masses, with lifetime of several billion years, rules out tachyons of mass $m > 3 \times 10^9$ GeV. This means there cannot exist any tachyons associated with unification scales or quantum gravity. So while there already exists theoretical reasons to be skeptical of tachyons, our work provides a complementary direct observational constraint.