Constraining Effective Self Interactions of Fermionic Dark Matter

TL;DR

This paper investigates the constraints on fermionic dark matter self interactions using an effective field theory approach, analyzing how interaction parameters vary with dark matter mass and velocity, and comparing with astrophysical observations.

Contribution

It provides a model-independent analysis of fermionic dark matter self interactions, deriving constraints on effective couplings from astrophysical data and exploring their dependence on mass and velocity.

Findings

Effective couplings decrease with increasing dark matter mass.

Some interactions' couplings decrease with velocity, others remain constant.

Astrophysical observations constrain the parameter space of self interaction models.

Abstract

The idea of Dark Matter (DM) with self interaction was invoked to resolve a number of discrepancies between the simulation based predictions by collisionless cold DM and the astrophysical observations on galactic and subgalactic scales. Evidences for self interaction would have striking implications for particle nature of DM. In order to reconcile such astrophysical observations for self interaction with particle properties for DM, we consider the general scenario of self interacting Dirac fermionic DM, $\chi$. Also since the exact particle physics model for DM is yet to be probed, we simply adopt the effective model independent framework for DM self interaction which occurs via the most general effective 4-fermion operators invariant under both Lorentz and CPT transformations. From the thorough investigation of the interrelations among the parameters in this framework, namely, the effective DM self couplings ($G_{i}$), DM mass ($m_{\chi}$) and relative velocity ($v_{\rm rel}$), it can be inferred that $G_{i}$ decrease with increasing $m_{\chi}$ for a given DM self interaction strength. Moreover, for few types of effective operators the values of $G_{i}$ fall off with increasing $v_{\rm rel}$ while they remain roughly constant for a wide range of $v_{\rm rel}$ for other cases. In addition, the parameter space in this framework is constrained by the claimed observational results of ${\sigma \over m_{\chi}}$ on cluster scales (Abell 3827, Bullet Cluster) after averaging the DM self interaction cross sections over DM velocity distribution in the cluster. This puts interesting constraints on the values of effective DM self couplings for different fermionic DM masses for various effective operators (scalar, vector, etc.) of DM self interactions in this scenario. Some other implications of DM effective self interaction are also discussed in this model independent framework.