Speaker
Description
The aim of this work is to evaluate the effect of a non-standard electron mass $m_e$ in the early Universe picture, in particular considering the neutrino decoupling scenario and Big Bang Nucleosynthesis (BBN).
In the standard case, neutrino interactions with electrons in the early universe maintain the former in equilibrium with the thermal plasma until before electron-positron pairs annihilate away. Modifying the electron mass changes the time at which this happens, thus affecting the neutrino energy density and consequently on the effective number of relativistic species, $N_{\mathrm{eff}}$.
On the other hand, during BBN, weak interactions and therefore the neutron-proton relation depend on the value of the electron mass.
By comparing the light element abundances predicted by BBN with their observed values and applying constraints on $N_{\mathrm{eff}}$, we derive the earliest bound on the value of the electron mass in the early universe, which is remarkably similar to the one measured at terrestrial experiments nowadays. This confirms that the value of the electron mass has been constant throughout most of the life of the Universe.