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Translating current ALP photon coupling strength bounds to the Randall-Sundrum model

Shihabul Haque, Sourov Roy, Soumitra SenGupta

Abstract

In this article, we look at the current bounds on the coupling strength of axion-like particles (ALPs) with two photons in the context of the Randall-Sundrum (RS) model. We relate the coupling strength to the compactification radius that governs the size of the extra dimension in the RS warped geometry model and show how the current bounds on the ALP can be used to derive appropriate constraints on the size of the extra fifth dimension in the RS model. We show that the resulting constraints fail to resolve the gauge hierarchy problem for light/ultralight ALPs and require a massive ALP of at least $m_{a} \gtrsim 0.1$ [GeV] to be relevant in the context of the hierarchy problem when the gauge field is in the bulk.

Translating current ALP photon coupling strength bounds to the Randall-Sundrum model

Abstract

In this article, we look at the current bounds on the coupling strength of axion-like particles (ALPs) with two photons in the context of the Randall-Sundrum (RS) model. We relate the coupling strength to the compactification radius that governs the size of the extra dimension in the RS warped geometry model and show how the current bounds on the ALP can be used to derive appropriate constraints on the size of the extra fifth dimension in the RS model. We show that the resulting constraints fail to resolve the gauge hierarchy problem for light/ultralight ALPs and require a massive ALP of at least [GeV] to be relevant in the context of the hierarchy problem when the gauge field is in the bulk.

Paper Structure

This paper contains 6 sections, 39 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Axion Photon coupling in the Randall-Sundrum model
  3. Gauge field in the bulk
  4. Gauge field on the brane
  5. Analysis of current bounds
  6. Summary and discussion

Figures (4)

  • Figure 1: Suppression from the Planck scale in the RS model. The coloured solid lines depict the constant $m$ curves in this plane given by eqn. \ref{['mass']}. The dotted green line indicates the Planck scale. The intersection of the constant $m$ curves with the Planck scale gives us the value of $k r_C$ required for a suppression from the Planck scale to $m$.
  • Figure 2: Existing bounds on ALP/photon coupling strength. Bounds from astrophysics are given in green while those from colliders and beam dump experiments are given in yellow. The QCD axion line is shown in gold. The shaded bands represent the estimated range of coupling strengths for suppression to $0.1$ [TeV] (top edge) to $10$ [TeV] (bottom edge) in the RS model. The dotted lines within the bands represent coupling strengths for suppression to the TeV scale. Note that the coupling to the photons is set to $g_{a\gamma\gamma}/4$ which, in our model, is equal to $\beta/2M_p$ and the data is drawn from CJHAxionLimits for this and the following figures.
  • Figure 3: Bounds on $g_{a\gamma\gamma}$ for heavy ALPs. The shaded bands represent the estimated range of coupling strengths for suppression to $0.1$ [TeV] (top edge) to $10$ [TeV] (bottom edge) in the RS model. The dotted lines within the bands represent coupling strengths for suppression to the TeV scale.
  • Figure 4: Existing bounds on ALP/photon coupling strength including DM searches. Bounds from DM searches in colliders or the like are given in lavender while those from astrophysical DM searches are given in gray. The shaded bands represent the estimated range of coupling strengths for suppression to $0.1$ [TeV] (top edge) to $10$ [TeV] (bottom edge) in the RS model. The dotted lines within the bands represent coupling strengths for suppression to the TeV scale.