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Cosmological Higgs-Axion Interplay for a Naturally Small Electroweak Scale

J. R. Espinosa, C. Grojean, G. Panico, A. Pomarol, O. Pujolàs, G. Servant

TL;DR

This paper extends the cosmological relaxation approach to the electroweak hierarchy by introducing a second slow-rolling field σ that, together with a φ field, dynamically scans the Higgs mass and the barrier controlling φ’s evolution. The resulting double-scanner (CHAIN) framework allows a natural separation between the weak scale and a high new-physics cutoff up to around $2×10^9$ GeV, with only φ and σ remaining light and feebly coupled. One of the scalars, σ, can serve as a dark matter candidate, while φ decays and interactions yield potential cosmological signals in gamma-ray backgrounds and other observables; the framework also predicts distinct Higgs-portal couplings and long-lived states. The paper outlines the consistency conditions, quantum spreading limits, and cosmological implications, proposing testable signatures across cosmology and astrophysics, and highlights the need for a UV completion and detailed phenomenology in future work.

Abstract

Recently, a new mechanism to generate a naturally small electroweak scale has been proposed. It exploits the coupling of the Higgs to an axion-like field and a long era in the early universe where the axion unchains a dynamical screening of the Higgs mass. We present a new realization of this idea with the new feature that it leaves no signs of new physics up to a rather large scale, 10^9 GeV, except for two very light and weakly coupled axion-like states. One of the scalars can be a viable Dark Matter candidate. Such a cosmological Higgs-axion interplay could be tested with a number of experimental strategies.

Cosmological Higgs-Axion Interplay for a Naturally Small Electroweak Scale

TL;DR

This paper extends the cosmological relaxation approach to the electroweak hierarchy by introducing a second slow-rolling field σ that, together with a φ field, dynamically scans the Higgs mass and the barrier controlling φ’s evolution. The resulting double-scanner (CHAIN) framework allows a natural separation between the weak scale and a high new-physics cutoff up to around GeV, with only φ and σ remaining light and feebly coupled. One of the scalars, σ, can serve as a dark matter candidate, while φ decays and interactions yield potential cosmological signals in gamma-ray backgrounds and other observables; the framework also predicts distinct Higgs-portal couplings and long-lived states. The paper outlines the consistency conditions, quantum spreading limits, and cosmological implications, proposing testable signatures across cosmology and astrophysics, and highlights the need for a UV completion and detailed phenomenology in future work.

Abstract

Recently, a new mechanism to generate a naturally small electroweak scale has been proposed. It exploits the coupling of the Higgs to an axion-like field and a long era in the early universe where the axion unchains a dynamical screening of the Higgs mass. We present a new realization of this idea with the new feature that it leaves no signs of new physics up to a rather large scale, 10^9 GeV, except for two very light and weakly coupled axion-like states. One of the scalars can be a viable Dark Matter candidate. Such a cosmological Higgs-axion interplay could be tested with a number of experimental strategies.

Paper Structure

This paper contains 10 sections, 46 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Double scanner mechanism
  3. Consistency requirements for a small weak scale
  4. Quantum spreading
  5. Cosmological signatures
  6. Properties of ${\hbox{\boldmath{$\phi$}}}$ and ${\hbox{\boldmath{$\sigma$}}}$
  7. Impact of ${\hbox{\boldmath{$\phi$}}}$ and ${\hbox{\boldmath{$\sigma$}}}$ on standard cosmological predictions
  8. Conclusion
  9. A partial UV completion of the model
  10. Relaxation in a two Higgs doublet scenario

Figures (3)

  • Figure 1: Left: Scalar potential in the $\{\phi,{\sigma}\}$ plane. The band without barriers is in green while the barriers getting high(er) are dark(er) brown. The blue line shows a possible slow-roll cosmological trajectory of the fields during inflation. The dashed purple line is the critical line for EWSB. Right: Classical time evolution of $\phi$ (blue curve) in the potential on the left. The black lines show the extremal points of the potential, with closely spaced minima (bold) and maxima (thin) alternating. (Arbitrary units and scales in both plots.)
  • Figure 2: Sketch of the four stages in the evolution of $\phi$, marked by the blue dot, in the time-dependent effective potential for $\phi$ obtained after integrating out $\sigma$ and $H$ but corresponding to the same potential as in Fig. \ref{['fig:V2Dphit']}. (Arbitrary units and scales.)
  • Figure 4: Left: Diagram generating $\phi \overline NN$ at the radiative level. Middle: Diagram contributing to the coupling $\overline NN|H|^2$. Right: Diagram generating an $O(\epsilon^2)$ contribution to $(\overline NN)^2$.