Primordial gravitational waves in non-minimally coupled chromo-natural inflation

Dimastrogiovanni, Ema; Fasiello, Matteo; Michelotti, Martino; Pinol, Lucas

doi:10.1088/1475-7516/2024/02/039

Cited by 8 publications

(1 citation statement)

References 85 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This family of models can be described as "spectator chromo-natural inflation" (SCNI) and their GW spectra are directly related to the shape of the axion potential [28]. Currently, the dynamics of spectator non-Abelian gauge fields during inflation is an active research direction [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47].…”

Section: Introductionmentioning

confidence: 99%

Backreaction of axion-SU(2) dynamics during inflation

Iarygina,

Sfakianakis,

Sharma

et al. 2024

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

We consider the effects of backreaction on axion-SU(2) dynamics during inflation. We use the linear evolution equations for the gauge field modes and compute their backreaction on the background quantities numerically using the Hartree approximation. We show that the spectator chromo-natural inflation attractor is unstable when back-reaction becomes important. Working within the constraints of the linear mode equations, we find a new dynamical attractor solution for the axion field and the vacuum expectation value of the gauge field, where the latter has an opposite sign with respect to the chromo-natural inflation solution. Our findings are of particular interest to the phenomenology of axion-SU(2) inflation, as they demonstrate the instability of the usual trajectory due to large backreaction effects. The viable parameter space of the model becomes significantly altered, provided future non-Abelian lattice simulations confirm the existence of the new dynamical attractor. In addition, the backreaction effects lead to characteristic oscillatory features in the primordial gravitational wave background that are potentially detectable with upcoming gravitational wave detectors.

show abstract

Section: Introductionmentioning

confidence: 99%

Backreaction of axion-SU(2) dynamics during inflation

Iarygina,

Sfakianakis,

Sharma

et al. 2024

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

show abstract

Gravitational axiverse spectroscopy: seeing the forest for the axions

Dimastrogiovanni,

Fasiello,

Leedom

et al. 2024

J. High Energ. Phys.

View full text Add to dashboard Cite

We consider inflationary models with multiple spectator axions coupled to dark gauge sectors via Chern-Simons (CS) terms. The energy injection into Abelian gauge fields from the axions engenders a multi-peak profile for scalar and tensor spectra. We highlight the constraining power of CMB spectral distortions on the scalar signal and discuss the conditions under which spectator sectors can account for the recently observed stochastic gravitational wave (GW) background in the nHz range. Given the tantalizing prospect of a multi-peak “GW forest” spanning several decades in frequency, we elaborate on possible ultraviolet origins of the spectator models from Type IIB orientifolds. String compactifications generically produce a multitude of axions, the “Axiverse”, from dimensional reduction of p-form gauge fields. The CS coupling of such axions to dark gauge fields in the worldvolume theory of D7-branes can be tuned via multiple brane wrappings and/or quantized gauge field strengths. If string axions coupled to Abelian gauge fields undergo slow-roll during inflation, they produce GW signals with peaked frequency distribution whose magnitude depends on the details of the compactification. We discuss the restrictions on spectator models from consistency and control requirements of the string compactification and thereby motivate models that may live in the string landscape as opposed to the swampland.

show abstract

Chromo-natural inflation supported by enhanced friction from Horndeski gravity

Murata,

Kobayashi

2024

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

We study the extension of the chromo-natural inflation model by incorporating nonminimal coupling between the axion field and gravity. Nonminimal coupling is introduced so that it enhances friction in the axion's equation of motion and thus supports slow-roll inflation. This enhanced friction effectively delays the activation of the gauge field, thereby preventing the overproduction of gravitational waves in the CMB scale. We extend previous results by describing the nonminimal coupling in a general and unifying way utilizing Horndeski gravity. This allows us to explore systematically and comprehensively possible enhanced friction models of chromo-natural inflation consistent with observations. We find a novel enhanced friction model that shows better agreement (within 1σ) with CMB measurements than the previous nonminimally coupled chromo-natural inflation model. The gravitational-wave spectrum starts to rise at some wavenumber due to retarded activation of the gauge field in the late stage of inflation. We show how one can identify the wavenumber at which this occurs based on the background evolution and present a universal analytic formula for the gravitational-wave spectrum that can be used for any enhanced friction model of chromo-natural inflation.

show abstract

Primordial gravitational waves in non-minimally coupled chromo-natural inflation

Cited by 8 publications

References 85 publications

Backreaction of axion-SU(2) dynamics during inflation

Backreaction of axion-SU(2) dynamics during inflation

Gravitational axiverse spectroscopy: seeing the forest for the axions

Chromo-natural inflation supported by enhanced friction from Horndeski gravity

Contact Info

Product

Resources

About