Speaker
Description
In the cosmological concordance model, dark matter is assumed to be cold,
non-interacting and covariantly conserved. An interesting possibility to
consider is a violation of the third assumption in this simple picture,
namely the conversion of a small fraction of dark matter to an invisible
form of radiation.
So far, surprisingly little attention has been given to this option without
theoretical bias towards a specific scenario like decaying dark matter.
Here I will discuss how cosmic microwave and large-scale structure
observations can probe dark matter conversion in a model-independent way,
thus putting a conservative bound on how much dark matter could have
disappeared at any point during the cosmological evolution. For late
conversion times, but still before the onset of structure formation,
such a 'disappearance' of a few percent of dark matter would even
mitigate some of the well-known tensions between these datasets.
There is a variety of more concrete scenarios that can be mapped to this
general idea, such as decaying dark matter or merging primordial black holes.
In the second part of the talk, I will discuss yet another concrete particle
physics realization, featuring a second era of dark matter annihilation
after thermal freeze-out. As a bonus, this model naturally allows for
velocity-dependent dark matter self-interactions strong enough to affect
structure formation at dwarf galaxy scales in potentially observable ways.
