The photo-philic QCD axion

Journal of High Energy Physics, Jan 2017

We propose a framework in which the QCD axion has an exponentially large coupling to photons, relying on the “clockwork” mechanism. We discuss the impact of present and future axion experiments on the parameter space of the model. In addition to the axion, the model predicts a large number of pseudoscalars which can be light and observable at the LHC. In the most favorable scenario, axion Dark Matter will give a signal in multiple axion detection experiments and the pseudo-scalars will be discovered at the LHC, allowing us to determine most of the parameters of the model.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2FJHEP01%282017%29095.pdf

The photo-philic QCD axion

Received: December Published for SISSA by Springer Marco Farina 0 1 3 6 7 Duccio Pappadopulo 0 1 3 4 7 Fabrizio Rompineve 0 1 3 4 5 7 Andrea Tesi 0 1 2 3 7 Open Access 0 1 3 7 c The Authors. 0 1 3 7 0 Philosophenweg 19 , 69120 Heidelberg , Germany 1 New York , NY 10003 , U.S.A 2 Enrico Fermi Institute, Department of Physics, University of Chicago 3 136 Frelinghuisen Road , Piscataway, NJ 08854 , U.S.A 4 Center for Cosmology and Particle Physics, Department of Physics, New York University 5 Institute for Theoretical Physics, University of Heidelberg 6 New High Energy Theory Center, Department of Physics, Rutgers University 7 5620 S. Ellis Ave , Chicago, IL 60637 , U.S.A We propose a framework in which the QCD axion has an exponentially large coupling to photons, relying on the \clockwork" mechanism. We discuss the impact of present and future axion experiments on the parameter space of the model. In addition to the axion, the model predicts a large number of pseudoscalars which can be light and observable at the LHC. In the most favorable scenario, axion Dark Matter will give a signal in multiple axion detection experiments and the pseudo-scalars will be discovered at the LHC, allowing us to determine most of the parameters of the model. axion; Beyond Standard Model; CP violation 1 Introduction 2 3 4 A lightning review of axion physics The standard QCD axion Variations over KSVZ The clockwork QCD axion The clockwork mechanism A photo-philic QCD axion Clockwork axion window: constraints and signals Phenomenology of clockwork pseudoscalars Discussion and outlook The strong CP problem arises from the experimental observation that CP symmetry is respected by strong interactions with very high precision. In particular, bounds on the neutron electric dipole moment (nEDM) at the level of dn < 3 the QCD theta angle to be tiny QCD . 10 10. A very elegant solution to this puzzle is embodied by the QCD axion [2{4]. The axion is a pseudo-Nambu-Goldstone boson with a non vanishing potential generated by strong interactions, which dynamically relaxes the -angle to 0. Furthermore, the energy density stored in the oscillations of the eld around the minimum of its potential constitute, in an expanding universe, a viable cold Dark Matter (DM) candidate. For all these reasons, the QCD axion represents a minimal and 10 26 e cm [1], require compelling extension of the Standard Model (SM). Many experiments have been built to detect axion DM, with many others that will be operating in the near future. Interestingly, most of them rely on the existence of a coupling between the axion eld a and the photons, described by the interaction lagrangian The coupling ga is generally non vanishing for the QCD axion, and typical models display a strong correlation between the axion mass and the coupling to photons Currently, only a very small fraction of the QCD axion DM window is being probed experimentally by the ADMX experiment [5]. Existent proposals for future experiments, like improvement of the ADMX setup [6] or new axion detection techniques like ABRACADABRA [7] are expected to increase the sensitivity on the parameter space de ned by eq. (1.2), but they are still only able to cover a fraction of the whole QCD axion DM window. Most of the constraining power of axion DM detection experiments reside in the region, outside of the range roughly de ned by eq. (1.2). It is however important to keep in mind that the strong correlation between ma and described by eq. (1.2) is not a generic consequence of solving the strong CP problem with an axion. The purpose of this paper is to show that the coupling ga can indeed be arbitrarily large without spoiling CP conservation by strong interactions. We will show, for the rst time, how this is indeed possible using a special realization of the clockwork mechanism introduced by [8, 9] (see also [10] for a broad overview, and [11] for an application to in ation). The existence of models in which the QCD axion couples to photons with arbitrary strength broadens the scope of experiments like ADMX and ABRACADABRA, and opens up region in the axion parameter space covered by more than one experiments leading to a rich phenomenology with multiple signals and possible collider smoking guns for our The structure of the paper is as follows. In section 2 we review the axion solution of the strong CP problem, its viability as a cold Dark Matter (DM) candidate, and the existing and planned experiments to detect it. As the majority of these experiments relies on the coupling of the axion to photons, in section 3 we review the predictions of the simplest QCD axion models showing that they imply a very strong correlation between this coupling and the axion mass. In section 4 we review the `clockwork mechanism' which allows to obtain exponentially large axion decay constants and we show how this can be used to get arbitrarily large couplings of the axion to photons without spoiling its solution to th (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2FJHEP01%282017%29095.pdf

Marco Farina, Duccio Pappadopulo, Fabrizio Rompineve, Andrea Tesi. The photo-philic QCD axion, Journal of High Energy Physics, 2017, pp. 95, Volume 2017, Issue 1, DOI: 10.1007/JHEP01(2017)095