Gravitational Baryogenesis

TL;DR

It is shown that a gravitational interaction between the derivative of the Ricci scalar curvature and the baryon-number current dynamically breaks CPT in an expanding Universe and, combined with baryON-number-violating interactions, can drive the Universe towards an equilibrium bARYon asymmetry that is observationally acceptable.

Abstract

We show that a gravitational interaction between the derivative of the Ricci scalar curvature and the baryon-number current dynamically breaks CPT in an expanding universe and, combined with baryon-number-violating interactions, can drive the universe towards an equilibrium baryon asymmetry that is observationally acceptable.

Figures (2)

• Figure 1: The range of $T_{RD}$, $M_B$ and $w$ that can generate an observationally acceptable baryon asymmetry assuming a dimension five ($n=1$) baryon number violating operator and no significant entropy production after decoupling is shown in dark gray and light gray. In supersymmetric theories, where the gravitino decays rapidly to an LSP with $m_{LSP} \approx 100$ GeV, the allowed region is restricted to the dark gray region only to avoid overclosure of the universe by LSP's. Both light and dark gray regions are allowed if the $m_{LSP} \ll 100$ GeV, if the LSP decays, if the gravitino is lighter than keV, or if there is no supersymmetry.
• Figure 2: The range of $T_{RD}$, $M_B$ and $w$ that can generate an observationally acceptable baryon asymmetry and avoid overclosure of the universe by stable LSP's expands to cover essentially both the light and dark gray regions in Fig. \ref{['fig:D5']}if we allow for entropy to be produced after the baryon-number violating interactions and gravitinos decouple. For each $w$, the allowed line in Fig. \ref{['fig:D5']} becomes an allowed strip (shown for two cases in the Figure) because we now include the possibility that the baryon asymmetry may be overproduced at decoupling to some degree and brought to its proper value by entropy production after decoupling. For the case $w=0.5$, we indicate along the strip the values of $n_B/s$ before dilution. The additional entropy reduces the gravitino/LSP density, thereby opening up the allowed range of $T_{RD}$ and $M_B$.