# Gamma-ray flux limits from nearby brown dwarfs: Implications for dark matter annihilating into long-lived mediators.

- Institution: CERN
- Department: Eucapt Conferences
- Speaker: Pooja BHATTACHARJEE
- Year: 2023
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3015407)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

Brown dwarfs (BDs) are celestial objects representing the link between the least massive main-sequence stars and giant gas planets. I will present a recent analysis (Bhattacharjee et al.,2023) where consider a sample of nine nearby ($<$ 11 pc distance), cold and old BDs and look for gamma-ray signal from the direction of these objects using 13 years of \textit{Fermi}-LAT data. In the absence of any gamma-ray excess, we set 95\% confidence level upper limits on the gamma-ray flux with a binned-likelihood approach.

I will then show how this null result can be used to constrain particle dark matter (DM). If the DM of the universe is constituted of particles with non-negligible couplings to the standard model, BDs may efficiently accumulate them through scatterings. DM particles eventually thermalize and can annihilate into light, long-lived, mediators which later decay into photons outside the BD.

Within this framework, we set a stacked upper limit on the DM-nucleon elastic scattering cross section at the level $\sim 10^{-38}$ cm$^{2}$ for DM masses below 10 GeV. Our limits are comparable to similar bounds from the capture of DM particles in celestial objects but have the advantage of covering a larger portion of the parameter space in mediator decay length and DM mass and being less affected by DM modeling uncertainties.

Reference: Bhattacharjee et al.,2023 - ``Gamma-ray flux limits from brown dwarfs: Implications for dark matter annihilating into long-lived mediators'' -Pooja Bhattacharjee, Francesca Calore, and Pasquale Dario Serpico - Phys. Rev. D 107, 043012 – Published 10 February 2023.

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## Lectures

1. [Gamma-ray flux limits from nearby brown dwarfs: Implications for dark matter annihilating into long-lived mediators.](https://invisiblenetwork.ai/learn/cern/3015407/99c0b7c4cd30), 7 min (CERN's player)