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Phenomenology of a Pseudo-Scalar Inflaton: Naturally Large Nongaussianity
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Many controlled realizations of chaotic inflation employ pseudo-scalar axions. Pseudo-scalars \phi are naturally coupled to gauge fields through c \phi F \tilde{F}. In the presence of this coupling, gauge field quanta are copiously produced by the rolling inflaton. The produced gauge quanta, in turn, source inflaton fluctuations via inverse decay. These new cosmological perturbations add incoherently with the "vacuum" perturbations, and are highly nongaussian. This provides a natural mechanism to generate large nongaussianity in single or multi field slow-roll inflation. The resulting phenomenological signatures are highly distinctive: large nongaussianity of (nearly) equilateral shape, in addition to detectably large values of both the scalar spectral tilt and tensor-to-scalar ratio (both being typical of large field inflation). The WMAP bound on nongaussianity implies that the coupling, c, of the pseudo-scalar inflaton to any gauge field must be smaller than about 10^{2} M_p^{-1}.
Forward citations
Cited by 9 Pith papers
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Gravitational waves from axion inflation in the gradient expansion formalism. Part I. Pure axion inflation
In pure axion inflation, detectable gravitational wave signals arise only in parameter regions with strong backreaction that violate the upper bound on ΔN_eff.
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Schwinger effect in axion inflation on a lattice
Lattice simulations show that Schwinger currents saturate gauge-field production in axion inflation, yielding universal conductivity and magnetic-field values at the onset of strong backreaction.
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Axion Inflation from Heavy-Fermion One-Loop Effects
One-loop integration of a heavy fermion with inflaton-dependent mass in axion inflation generates localized gauge-field production and a detectable chiral gravitational-wave signal in the deci-hertz range.
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A universal scaling law for gravitational waves induced during inflation
Induced gravitational waves during inflation obey a universal tensor spectral index formula that yields near scale-invariance for slow-roll expansion regardless of the source field's original spectrum.
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Gravitational waves from axion inflation in the gradient expansion formalism. Part II. Fermionic axion inflation
Schwinger fermion production in axion inflation damps gauge fields, enabling observable primordial gravitational waves in LISA/ET bands while satisfying ΔN_eff limits and identifying a new damped-oscillation backreact...
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Lattice study of primordial black hole formation in bumpy axion inflation
Lattice simulations of bumpy axion U(1) inflation in the strong backreaction regime generate curvature perturbations large enough for primordial black holes to comprise all dark matter.
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Primordial black hole dark matter from axion inflation
PBHs generated by axion inflation with gauge-field coupling can comprise all dark matter in the asteroidal mass range while producing a LISA-measurable stochastic GW background.
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The End of the First Act: Spectral Running, Interacting Dark Radiation, and the Hubble Tension in Light of ACT DR6 Data
Including spectral running α_s, β_s and self-interacting dark radiation relaxes the ACT DR6 bound on ΔN_eff to <0.58 and lowers the Hubble tension to 2.2σ with three extra parameters.
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Pure Natural Inflation Passes the ACT
Pure natural inflation remains viable against latest ACT+DESI constraints, with a non-trivial fraction of parameter space allowed under standard reheating scenarios.
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