Physics Letters B 750 (2015) 552–558
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
An alternative interpretation for cosmic ray peaks
Doojin Kim
a
, Jong-Chul Park
b,∗
a
Physics Department, University of Florida, Gainesville, FL 32611, USA
b
Department of Physics, Chungnam National University, Daejeon 305-764, Republic of Korea
a r t i c l e i n f o a b s t r a c t
Article history:
Received
6 September 2015
Received
in revised form 23 September
2015
Accepted
29 September 2015
Available
online 3 October 2015
Editor:
G.F. Giudice
We propose an alternative mechanism based upon dark matter (DM) interpretation for anomalous peak
signatures
in cosmic ray measurements, assuming an extended dark sector with two DM species. This
is contrasted with previous effort to explain various line-like cosmic-ray excesses in the context of DM
models where the relevant DM candidate directly annihilates into Standard Model (SM) particles. The
heavier DM is assumed to annihilate to an on-shell intermediate state. As the simplest choice, it decays
directly into the lighter DM along with an unstable particle which in turn decays to a pair of SM states
corresponding to the interesting cosmic anomaly. We show that a sharp continuum energy peak can be
readily generated under the proposed DM scenario, depending on dark sector particle mass spectra.
Remarkably, such a peak is robustly identified as half the mass of the unstable particle. Furthermore,
other underlying mass parameters are analytically related to the shape of energy spectrum. We apply
this idea to the two well-known line excesses in the cosmic photon spectrum: 130 GeV γ -ray line and
3.5 keV X-ray line. Each observed peak spectrum is well-reproduced by theoretical expectation predicated
upon our suggested mechanism, and moreover, our resulting best fits provide rather improved χ
2
values.
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
Dark matter (DM) is a necessary component in the time evo-
lution
of our Universe, and its existence has been supported by a
tremendous amount of astrophysical and cosmological evidence for
which the relevant observations are made mostly based upon the
gravitational interaction of DM (see Ref. [1] for a general review).
In fact, none of the Standard Model (SM) particles can explain
various DM-related phenomena, so that the detection of any DM
candidates can be not only exciting per se but a strong sign of
new physics framework beyond the Standard Model (BSM). A great
deal of experimental effort to detect DM signals has been made in
three different directions such as i) direct detection experiments
by observing recoil energy of target nuclei scattered off by DM,
ii) indirect detection experiments by observing cosmic rays orig-
inating
from DM annihilation or decay, and iii) collider searches
(for example, at the Large Hardon Collider at CERN) by actively
producing DM candidates and exploiting their collider signatures.
These three avenues to DM detection are complementary to one
another, and have set the bounds of the viable DM mass and the
*
Corresponding author.
E-mail
addresses: immworry@ufl.edu (D. Kim), jcpark@cnu.ac.kr (J.-C. Park).
associated cross section (see Ref. [2] and references therein for re-
view).
1
Among those experimental attempts, indirect detection experi-
ments
have received particular attention as many of them have re-
ported
anomalous observations potentially signaling the presence
of DM candidates at the locus of cosmic ray sources. For instance,
PAMELA [4], Fermi-LAT [5], and AMS-02 [6] found quite a marked
rise of the positron fraction in the energy range from roughly 10
to 200 GeV, and similarly ATIC [7], FERMI-LAT [8], and HESS [9]
reported
an excess in the positron–electron combined energy spec-
trum
between 100 and 1000 GeV. Several photon channels showed
intriguing excesses such as 3.5 keV line [10,11], 511 keV line [12],
GeV bump [13], and 130 GeV line [14,15]. The positron excesses
and the Galactic Center (GC) GeV γ -ray excess are featured by a
continuum bump, while the other three X/γ -ray excesses showed
a sharp peak within a very narrow energy range.
The
latter class of excesses are particularly interesting because
they can be readily connected to the DM interpretation. As typical
DM candidates behave non-relativistically, the photon energy from
1
Recently, Ref. [3] proposed a general scenario, dubbed “Inflatable DM models”,
within the context of which many well-motivated DM models having too large
production of DM can be remedied, hence evade the bounds without tuning of un-
derlying
parameters.
http://dx.doi.org/10.1016/j.physletb.2015.09.070
0370-2693/
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.