Phys. Rev. D 85, 123543 (2012) - Lower limits on the strengths of gamma ray lines from WIMP dark matter annihilation

Lower limits on the strengths of gamma ray lines from WIMP dark matter annihilation

Kevork N. Abazajian, Prateek Agrawal, Zackaria Chacko, and Can Kilic

Phys. Rev. D 85, 123543 – Published 26 June 2012

Abstract

We study the spectra of gamma ray signals that arise from dark matter annihilation in the Universe. We focus on the large class of theories where the photon spectrum includes both continuum spectrum of gamma rays that arise from annihilation into standard model states at tree level, as well as monochromatic gamma rays arising from annihilation directly into two photons at the one-loop level. In this class of theories we obtain lower bounds on the ratio of the strength of the gamma ray line relative to the gamma ray continuum as a function of the dark matter mass and spin. These limits are obtained from the unitarity relation between the tree-level amplitude of the primary annihilation channel and the imaginary part of the loop-level amplitude for annihilation directly into photons, with the primary decay products running in the loop. These results are exact in the limit that dark matter annihilation at tree level is exclusively to a single standard model species, occurs through the lowest partial wave and respects $C P$ . Away from this limit the bounds are approximate. Our conclusions agree with known results in the literature for the cases of the minimal supersymmetric standard model, universal extra dimensions and the littlest Higgs with $T$ parity. We use the Fermi-LAT observations to translate these limits into upper bounds on the dark matter annihilation cross section into any specific standard model state.

Received 19 November 2011

DOI:https://doi.org/10.1103/PhysRevD.85.123543

Authors & Affiliations

Kevork N. Abazajian^1,2, Prateek Agrawal¹, Zackaria Chacko¹, and Can Kilic³

¹Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
²Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
³Theory Group, Department of Physics and Texas Cosmology Center, The University of Texas at Austin, Austin, Texas 78712, USA

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 85, Iss. 12 — 15 June 2012

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Model independence of the lower bound on the ratio of loop and tree annihilation cross sections shown graphically. The $X$ particle is a SM state, and $χ$ is the dark matter particle. For purposes of obtaining a limit, dark matter annihilation can be modeled by the decay of a boson, $Φ$ .Reuse & Permissions
Figure 2
Spectral flux $E^{2} d Φ / d E$ in the continuum relative to the lower limit for the line obtained from our calculation. We show results for annihilation into $W W$ (upper panel) and $b \bar{b}$ (lower panel) for a Majorana fermion dark matter. The annihilation cross section was taken to be $⟨ σ_{A} v ⟩ = 3 \times 10^{- 26} {cm}^{3} s^{- 1}$ and $m_{χ} = 100 GeV$ . The width of the line is set by the Fermi-LAT resolution at 100 GeV, 11% FWHM.Reuse & Permissions
Figure 3
For the supersymmetry model of 16, 17 where the neutralino DM annihilates through a loop of $W$ bosons into a pair of photons, we plot the ratio of the part of the annihilation cross section arising from the imaginary part of the amplitude to the full cross section.Reuse & Permissions
Figure 4
For the littlest Higgs model with $T$ parity [25, 26] where the DM annihilates into a pair of photons through an $s$ -channel Higgs boson, we plot the ratio of the part of the annihilation cross section arising from the imaginary part of the amplitude to the full cross section. The contribution purely due to the $W$ ’s in the loop and purely due to the top quark in the loop is shown.Reuse & Permissions
Figure 5
For the UED model of 22, 23 where the KK-photon DM annihilates into a pair of photons through a loop of light fermions, we plot the ratio of the part of the annihilation cross section arising from the imaginary part of the amplitude to the full cross section as a function of the ratio of the KK-photon mass to the KK-fermion mass.Reuse & Permissions
Figure 6
Upper, middle and lower rows of panels show current and future 95% C.L. constraints on dark matter annihilation channels in the scalar, Majorana, and vector dark matter cases, respectively. The colored regions are from constraints from the isotropic DGRB on Galactic and extragalactic dark matter annihilation, as described in the text. The diagonally hatched regions are from current constraints from Fermi-LAT on the minimal line contribution in the respective channels, as discussed in the text. The vertically hatched regions are forecasts for the limits after 10 years of observation with Fermi-LAT, assuming Poisson statistics at the current energy resolution. In the case of scalar dark matter to $W W$ (upper right panel), the solid line indicates the true limit for ultrarelativistic $W W$ production, and the nonoutlined hatched region is an interpolation of the limit to the nonrelativistic regime at $m_{χ} \sim 100 GeV$ .Reuse & Permissions

Physical Review D

covering particles, fields, gravitation, and cosmology

Lower limits on the strengths of gamma ray lines from WIMP dark matter annihilation

Kevork N. Abazajian, Prateek Agrawal, Zackaria Chacko, and Can Kilic

Phys. Rev. D 85, 123543 – Published 26 June 2012

Abstract

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review D

covering particles, fields, gravitation, and cosmology

Lower limits on the strengths of gamma ray lines from WIMP dark matter annihilation

Kevork N. Abazajian, Prateek Agrawal, Zackaria Chacko, and Can Kilic

Phys. Rev. D 85, 123543 – Published 26 June 2012

Abstract

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation