A Tale of Tails: Dark Matter Interpretations of the Fermi GeV Excess in Light of Background Model Systematics (1411.4647v2)

Abstract: Several groups have identified an extended excess of gamma rays over the modeled foreground and background emissions towards the Galactic center (GC) based on observations with the Fermi Large Area Telescope. This excess emission is compatible in morphology and spectrum with a telltale sign from dark matter (DM) annihilation. Here, we present a critical reassessment of DM interpretations of the GC signal in light of the foreground and background uncertainties that some of us recently outlaid in Calore et al. 2014. We find that a much larger number of DM models fits the gamma-ray data than previously noted. In particular: (1) In the case of DM annihilation into $\bar{b}b$, we find that even large DM masses up to $m_\chi \simeq$ 74 GeV are allowed with a $p$-value $> 0.05$. (2) Surprisingly, annihilation into non-relativistic hh gives a good fit to the data. (3) The inverse Compton emission from $\mu^+\mu^-$ with $m_\chi\sim$ 60-70 GeV can also account for the excess at higher latitudes, $|b|>2^\circ$, both in its spectrum and morphology. We also present novel constraints on a large number of mixed annihilation channels, including cascade annihilation involving hidden sector mediators. Finally, we show that the current limits from dwarf spheroidal observations are not in tension with a DM interpretation when uncertainties on the DM halo profile are accounted for.

• The paper presents a critical reassessment of dark matter annihilation channels, showing that models including up to 74 GeV and nonrelativistic hh states can statistically fit the gamma-ray excess.
• The analysis highlights the impact of foreground and background modeling, demonstrating that inverse Compton signals from μ+μ− annihilation can meet both spectral and morphological criteria.
• The study quantifies uncertainties in DM cross-sections and explores mixed annihilation scenarios, thereby broadening the viable parameter space for dark matter interpretations.

Reassessment of Dark Matter Interpretations of the Galactic Center GeV Excess

The paper in question presents a critical evaluation of dark matter (DM) interpretations of the observed GeV gamma-ray excess at the Galactic Center (GC), focusing on the uncertainties linked to the modeling of foreground and background emissions. The authors discuss the possible origins of this excess, notably considering weakly interacting massive particles (WIMPs) as DM candidates, and they explore the spectrum of DM annihilation channels that could be responsible for the observed signal. This analysis considers recent estimates of foreground and background contributions that can significantly impact the derived characteristics of the gamma-ray excess signal.

The research finds that the excess emission could be explained by DM annihilation and that the gamma-ray spectrum allows for fitting with a variety of DM models. Particularly noteworthy is the allowance, contrary to prior analyses, for numerous DM scenarios fitting the gamma-ray data, and the indication that even high mass DM models up to around 74 GeV, annihilating into $\bar{b}b$, can provide a plausible fit, with statistical integrity beyond the 95\% confidence level. Moreover, annihilation into the nonrelativistic $hh$ final state also fits well, suggesting the possibility of a previously underestimated channel.

A remarkable extension of previous work is the reassessment of the inverse Compton scattering signal linked to $\mu^+\mu^-$ annihilation. Previous studies have largely ignored this aspect. This paper, however, posits that inverse Compton emission across higher latitudes, with DM annihilation ranging from 60 to 70 GeV, can meet both the morphological and spectral requirements to potentially account for the excess. This is contingent on specific cosmic ray propagation models, implying significant varying outcomes dependent on the choice of these models.

In the domain of mixed annihilation channels, the analysis explores complex mixtures of final states, such as hadronic and leptonic decay modes, further distinguishing the notable flexibility of DM interpretations under various branching ratios. For instance, combinations allowing for secondary particles like tau-leptons can still align well with observations, thereby offering a rich action space for model builders to explore novel DM scenarios that maintain congruence with current astrophysical constraints.

The paper also scrupulously revisits limits imposed by constraints from other astrophysical structures, notably dwarf spheroidal galaxies (dSphs). Current non-detections from dSphs, under specific assumptions about the DM density profile, do not significantly constrain the potential DM explanation for the GC excess. Nonetheless, should these limits further tighten, substantial tension could arise between what would be considered permissible at the GC and dSphs. The authors quantify potential cross-section uncertainties due to unknown halo parameters, suggesting variation by a factor of approximately 5, given the vast parameter space.

This research ultimately signifies a step forward in DM studies related to the GC GeV excess, underscoring the broad spectrum of DM models that are compatible with existing data. It advocates for an inclusive consideration of model uncertainties and theorizes several plausible configurations that warrant further investigation. Future research directions could focus on stricter constraints across different propagation models and assess the potential impact of upcoming observational data, which may finally tip the scale in favor of certain DM scenarios over others.