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N-vaton

Qing-Guo Huang

TL;DR

The paper introduces N-vaton, a multi-curvaton framework where many light scalar fields decay simultaneously, and uses the $\delta {\cal N}$ formalism to compute the resulting power spectrum and local-type non-Gaussianity $f_{NL}$. It derives both lower and upper bounds on $f_{NL}$, analyzes adiabaticity constraints, and shows how a red-tilted spectrum can arise when inflaton fluctuations contribute to the total power. A realistic realization with KKLT-type axions as curvatons is explored, employing a Marcenko-Pastur mass spectrum to model the mass distribution and providing explicit expressions for $P_\zeta^{nc}$ and $f_{NL}^{nc}$, along with a framework to compare with observational data. The work links string-theoretic moduli to cosmological observables, offering testable predictions for Planck-scale physics through measurements of $P_\zeta$, $f_{NL}$, and the tensor-to-scalar ratio $r$, and clarifies how multi-curvaton dynamics modify early-Universe signatures.

Abstract

In general there are a large number of light scalar fields in the theories going beyond standard model, such as string theory, and some of them can be taken as the candidates of curvatons. For simplicity, we assume all of curvatons have the same decay rate and suddenly decay into radiation at the same time. In order to distinguish this scenario from the more general case, we call it "N-vaton". We use $δ{\cal N}$ formalism to calculate the primordial power spectrum and bispectrum in N-vaton model and investigate various bounds on the non-Gaussianity parameter $f_{NL}$. A red tilted primordial power spectrum and a large value of $f_{NL}$ can be naturally obtained if the curvature perturbation generated by inflaton also makes a significant contribution to the primordial power spectrum. As a realistic N-vaton model, we suppose that the axions in the KKLT compactifications of Type IIB string theory are taken as curvatons and a rich phenomenology is obtained.

N-vaton

TL;DR

The paper introduces N-vaton, a multi-curvaton framework where many light scalar fields decay simultaneously, and uses the formalism to compute the resulting power spectrum and local-type non-Gaussianity . It derives both lower and upper bounds on , analyzes adiabaticity constraints, and shows how a red-tilted spectrum can arise when inflaton fluctuations contribute to the total power. A realistic realization with KKLT-type axions as curvatons is explored, employing a Marcenko-Pastur mass spectrum to model the mass distribution and providing explicit expressions for and , along with a framework to compare with observational data. The work links string-theoretic moduli to cosmological observables, offering testable predictions for Planck-scale physics through measurements of , , and the tensor-to-scalar ratio , and clarifies how multi-curvaton dynamics modify early-Universe signatures.

Abstract

In general there are a large number of light scalar fields in the theories going beyond standard model, such as string theory, and some of them can be taken as the candidates of curvatons. For simplicity, we assume all of curvatons have the same decay rate and suddenly decay into radiation at the same time. In order to distinguish this scenario from the more general case, we call it "N-vaton". We use formalism to calculate the primordial power spectrum and bispectrum in N-vaton model and investigate various bounds on the non-Gaussianity parameter . A red tilted primordial power spectrum and a large value of can be naturally obtained if the curvature perturbation generated by inflaton also makes a significant contribution to the primordial power spectrum. As a realistic N-vaton model, we suppose that the axions in the KKLT compactifications of Type IIB string theory are taken as curvatons and a rich phenomenology is obtained.

Paper Structure

This paper contains 14 sections, 137 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Primordial curvature perturbation
  3. Bound on the non-Gaussianity parameter $f_{NL}$
  4. Lower bound on $f_{NL}$
  5. Upper bound on $f_{NL}$
  6. Adiabatic condition
  7. The case with $m_i=m$ for $i=1,2,...,N$
  8. N-vaton vs. single-curvaton model
  9. Spectral index and non-Gaussianity
  10. Random matrix and typical mass spectrum in string theory
  11. Compare to experiments
  12. Discussions
  13. Appendix: $\zeta_r=\zeta_\phi\neq 0$
  14. Appendix: Another way to get a large non-Gaussianity in N-vaton model

Figures (3)

  • Figure 1: The function $f_1(v)$ and $f_2(v)$.
  • Figure 2: The function $\tau(v)$.
  • Figure 3: The function $d_1(v)$ and $d_2(v)$.