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Cosmological Constraints on Long-Lived Particles Using Dimension-Six Effective Operators

Mickael V. S. de Farias, Rodrigo Holanda, Matheus M. A. Paixao, Farinaldo S. Queiroz, Priscila V. dos Santos

Abstract

Long-lived particles (LLPs) provide an interesting window into physics beyond the Standard Model, offering characteristic signatures at colliders and in cosmology. In this work, we investigate LLPs decays into dark matter. If the lifetime of LLPs are longer than $10^4$s, the decay products can disrupt the synthesis of light nuclei in the early universe and alter Big Bang Nucleosynthesis (BBN) predictions. If the LLP is much heavier than the dark matter particle, the decay contributes to the number of effective neutrino species, $N_{eff}$. We describe these decays via dimension-six effective operators and outline the parameter space in which such decays obey cosmological bounds stemming from BBN, structure formation, Cosmic Microwave Background, and Baryon Acoustic Oscillation data.

Cosmological Constraints on Long-Lived Particles Using Dimension-Six Effective Operators

Abstract

Long-lived particles (LLPs) provide an interesting window into physics beyond the Standard Model, offering characteristic signatures at colliders and in cosmology. In this work, we investigate LLPs decays into dark matter. If the lifetime of LLPs are longer than s, the decay products can disrupt the synthesis of light nuclei in the early universe and alter Big Bang Nucleosynthesis (BBN) predictions. If the LLP is much heavier than the dark matter particle, the decay contributes to the number of effective neutrino species, . We describe these decays via dimension-six effective operators and outline the parameter space in which such decays obey cosmological bounds stemming from BBN, structure formation, Cosmic Microwave Background, and Baryon Acoustic Oscillation data.
Paper Structure (11 sections, 34 equations, 5 figures)

This paper contains 11 sections, 34 equations, 5 figures.

Table of Contents

  1. Introduction
  2. LLP Decays and $N_{eff}$
  3. Constraints
  4. CMB and BAO Surveys
  5. BBN constraints
  6. Spectral Distortions
  7. Structure Formation
  8. Entropy Injection
  9. Dimension-6 Effective Lagrangians
  10. Conclusions
  11. Acknowledgements

Figures (5)

  • Figure 1: BBN bounds based on light element abundances and CMB constraint stemming from spectral distortion of the CMB. See text for details. The green region delimits the parameter space that yields $\Delta N_{eff}=0.1-0.3$. Using the positive correlation between $\Delta N_{eff}$ and $H_0$ one could raise $H_0$ and alleviate the Hubble tension.
  • Figure 2: Diagrammatic representation of the decay $X_1 \rightarrow X_2 + \gamma$. In order to have relativistic production of dark matter, it is assumed that $m_{X_1}\gg m_{X_2}$.
  • Figure 3: Parameter space for the decay \ref{['ffgamma']}.Allowed regions in the long-lived particle ($m_{X_{1}}$) and dark matter ($m_{X_{2}}$) parameter space for different values of the energy scale $\Lambda$. The colored shaded area represents the BBN constrains $\tau \leq 10^4\,s$Alcaniz2022. The red lines indicates different values of the mother-to-daugther mass ratio.
  • Figure 4: Diagram representing of the decay $X_1 \rightarrow X_2 + \gamma$ decay, where $X_1$ and $X_2$ are both vector fields.
  • Figure 5: Parameter space for the decay \ref{['vvgamma']}. Again, The colored shaded area represents the BBN constrains $\tau \leq 10^4\,s$, whereas the red lines delineates different values of the ratio $m_{X_1}/m_{X_2}$.