Chiara Arina, Jan Hamann, Roberto Trotta, Yvonne Y Y Wong
We investigate the question of whether the recent modulation signal claimed
by CoGeNT is best explained by the dark matter (DM) hypothesis from a Bayesian
model comparison perspective. We consider five phenomenological explanations
for the data: no modulation signal, modulation due to DM, modulation due to DM
compatible with the total CoGeNT rate, and a signal coming from other physics
with a free phase but annual period, or with a free phase and a free period. In
each scenario, we assign to the free parameters physically motivated priors. We
find that the no modulation model is excluded with odds in excess of 10^5 : 1
when all energy bins are included in the analysis. The DM models are strongly
preferred over explanations due to other physics, even when astrophysical
uncertainties are taken into account and the impact of priors assessed.
However, the evidence for the DM model in which the modulation signal is
compatible with the total rate is significantly weaker than for a DM model in
which this prior is not implemented, a result driven mainly by the large
modulation amplitude observed in the energy range (0.9 - 3.0) keVee by CoGeNT.
Classical hypothesis testing also rules out the null hypothesis of no
modulation at the 4.5-sigma to 4.8-sigma level, depending on the details of the
alternative. Lastly, we investigate whether anisotropic velocity distributions
can help to mitigate the tension between the CoGeNT total and modulated rates,
and find encouraging results.
View original:
http://arxiv.org/abs/1111.3238
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