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A Parallel World in the Dark

Tetsutaro Higaki, Kwang Sik Jeong, Fuminobu Takahashi

TL;DR

The paper proposes a dark parallel world mirroring the SM and interacting with our sector only through gravity to address the baryon–dark matter and dark radiation coincidences. It derives a robust relation between the dark radiation density $\Delta N_{\rm eff}$ and the number of massive sterile neutrinos $N_s$, controlled by the light degrees of freedom and the p-neutrino mass hierarchy, via thermodynamic arguments. It identifies para-baryon dark matter (p-neutrons) with self-interactions and connects the baryon asymmetries of the two sectors through leptogenesis, with the DM abundance sensitive to the temperature ratio between sectors. It also discusses string-theory realizations (Calabi–Yau compactifications with D-branes) that naturally accommodate two sectors and the required mass scales and reheating dynamics, offering a coherent high-energy framework for the scenario.

Abstract

The baryon-dark matter coincidence is a long-standing issue. Interestingly, the recent observations suggest the presence of dark radiation, which, if confirmed, would pose another coincidence problem of why the density of dark radiation is comparable to that of photons. These striking coincidences may be traced back to the dark sector with particle contents and interactions that are quite similar, if not identical, to the standard model: a dark parallel world. It naturally solves the coincidence problems of dark matter and dark radiation, and predicts a sterile neutrino(s) with mass of ${\cal O}(0.1 - 1)$\,eV, as well as self-interacting dark matter made of the counterpart of ordinary baryons. We find a robust prediction for the relation between the abundance of dark radiation and the sterile neutrino, which can serve as the smoking-gun evidence of the dark parallel world.

A Parallel World in the Dark

TL;DR

The paper proposes a dark parallel world mirroring the SM and interacting with our sector only through gravity to address the baryon–dark matter and dark radiation coincidences. It derives a robust relation between the dark radiation density and the number of massive sterile neutrinos , controlled by the light degrees of freedom and the p-neutrino mass hierarchy, via thermodynamic arguments. It identifies para-baryon dark matter (p-neutrons) with self-interactions and connects the baryon asymmetries of the two sectors through leptogenesis, with the DM abundance sensitive to the temperature ratio between sectors. It also discusses string-theory realizations (Calabi–Yau compactifications with D-branes) that naturally accommodate two sectors and the required mass scales and reheating dynamics, offering a coherent high-energy framework for the scenario.

Abstract

The baryon-dark matter coincidence is a long-standing issue. Interestingly, the recent observations suggest the presence of dark radiation, which, if confirmed, would pose another coincidence problem of why the density of dark radiation is comparable to that of photons. These striking coincidences may be traced back to the dark sector with particle contents and interactions that are quite similar, if not identical, to the standard model: a dark parallel world. It naturally solves the coincidence problems of dark matter and dark radiation, and predicts a sterile neutrino(s) with mass of \,eV, as well as self-interacting dark matter made of the counterpart of ordinary baryons. We find a robust prediction for the relation between the abundance of dark radiation and the sterile neutrino, which can serve as the smoking-gun evidence of the dark parallel world.

Paper Structure

This paper contains 6 sections, 24 equations, 1 figure.

Table of Contents

  1. Introduction
  2. A dark parallel world
  3. Dark radiation and sterile neutrino
  4. Baryon and dark matter
  5. Implications from the string theory
  6. Discussion and conclusions

Figures (1)

  • Figure 1: The relation of the abundance of dark radiation $\Delta N_{\rm eff}$ and the effective number of massive sterile neutrinos $N_s$. The two solid lines correspond to the relation (\ref{['teq']}) for the normal (blue, lower) and inverted (red, upper) hierarchy, respectively. The relation (\ref{['tdiff']}) is similarly shown as dashed lines. The dark parallel sector leads to $\Delta N^{\rm BBN}_{\rm eff}>1.48$ along the gray lines.