[Paper Review] Mixed Wino-Axion Dark Matter in String/M Theory and the 130 GeV Gamma-line "Signal"

B. S. Acharya, Gordon Kane+3 more|arXiv (Cornell University)|May 25, 2012

Dark Matter and Cosmic Phenomena15 citations

TL;DR

This paper proposes that the tentative 130 GeV Fermi-LAT gamma-ray line signal arises from annihilation of 145 GeV Wino-like WIMPs into a Z boson and a photon, with the remaining dark matter component being axions. In the context of string/M-theory compactifications with low-energy supersymmetry, this model naturally predicts a mixed Wino-axion dark matter scenario with roughly equal abundances, consistent with cosmological constraints and offering falsifiable predictions for LHC and astrophysical observations.

ABSTRACT

String/M theory compactifications with low energy supersymmetry tend to predict that dark matter has two components: axions and WIMPs \cite{1004.5138,1204.2795}. In accord with this, we show that the tentative 130 GeV gamma-line signal reported in \cite{1204.2797} can be interpreted as arising from the annihilation of 145 GeV mass, Wino-like WIMPs into a Z-boson and a photon. In this context, the signal implies a second component of dark matter which we interpret as being composed of axions - the relative Wino/Axion abundances being approximately equal. Further predictions are implied: signals in both diffuse and monochromatic photons from dwarf spheroidal galaxies; monochromatic photons with energy 145 GeV; for the LHC, the Higgs boson mass has been predicted in this framework \cite{1112.1059}, and the current Higgs limits provide interesting constraints on the mass of the Gluino.

Motivation & Objective

• To interpret the tentative 130 GeV gamma-ray line signal from Fermi-LAT as arising from Wino-like WIMP annihilation into Zγ final states.
• To explore the implications of this signal within string/M-theory compactifications featuring low-energy supersymmetry and cosmological moduli physics.
• To determine the relative abundances of Wino-like WIMPs and axions in the dark matter component, consistent with cosmological constraints.
• To derive correlated, falsifiable predictions for particle physics observables, including Higgs and gaugino masses, within the framework.
• To assess the consistency of the model with existing constraints from diffuse and monochromatic gamma-ray searches in dwarf spheroidal galaxies and the Milky Way.

Proposed method

• Assumes the 130 GeV gamma-ray line signal originates from WIMP annihilation into Zγ final states, inferring a WIMP mass of approximately 145 GeV.
• Applies constraints from the observed annihilation cross-section and the requirement of thermal relic density to determine the relative abundances of Wino-like WIMPs and axions.
• Uses a top-down approach based on string/M-theory vacua with low-energy supersymmetry, where cosmological moduli physics favors Wino-like LSPs and predicts a dual axion component.
• Performs numerical spectrum calculations using SPheno to compute gaugino pole masses (gluino, bino) as functions of the gravitino mass and μ parameter, under varied input parameters.
• Evaluates consistency with Fermi-LAT limits on gamma-line signals from the Milky Way and diffuse gamma-ray excesses from dwarf spheroidal galaxies.
• Derives predictions for the Higgs boson mass and gaugino masses in models compatible with the 1112.1059 Higgs mass prediction, using the gravitino mass as a key input.

Experimental results

Research questions

• RQ1 Can the 130 GeV gamma-ray line signal be consistently explained by Wino-like WIMP annihilation into Zγ final states within string/M-theory compactifications?
• RQ2 What is the predicted relative abundance of Wino-like WIMPs and axions in the dark matter component, given the observed signal and cosmological constraints?
• RQ3 What are the implications of the signal for the masses of the gluino and bino in the context of low-energy supersymmetry and string/M-theory?
• RQ4 How do existing constraints from Fermi-LAT gamma-ray searches for monochromatic and diffuse lines affect the viability of the mixed Wino-axion dark matter model?
• RQ5 Can the model predict the Higgs boson mass and other particle physics observables in a way that is consistent with LHC data and theoretical constraints?

Key findings

• The 130 GeV gamma-ray line signal is best interpreted as arising from 145 GeV Wino-like WIMPs annihilating into Zγ final states, with a required annihilation cross-section of approximately 1.27–2.27 × 10⁻²⁷ cm³/s depending on the dark matter density profile.
• The model predicts that the Wino-like WIMP and axion components each contribute roughly 50% to the total dark matter abundance, consistent with cosmological constraints and string/M-theory predictions.
• For a gravitino mass m₃/₂ ≲ 80 TeV and μ < 0, the gluino pole mass is predicted to lie in the range 900–1180 GeV, while for μ > 0 it is 820–1100 GeV.
• The bino pole mass is predicted to be in the range 145–250 GeV, with a small spread of ≤10 GeV, regardless of the sign of μ.
• The model is consistent with current Fermi-LAT limits on gamma-line signals from the Milky Way and diffuse gamma-ray excesses from dwarf spheroidal galaxies, which further constrain the non-WIMP component of dark matter.
• The framework predicts a Higgs boson mass compatible with LHC hints, and correlates the gluino and bino masses with the gravitino mass, enabling falsifiable LHC signals.