Hybrid inflation model with Z_N-symmetric waterfall fields cancels quadratic radiative corrections for any N and logarithmic ones for N>2, yielding a stable inflaton potential and domain-wall-free reheating via Higgs-portal couplings.
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Completing Natural Inflation
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abstract
If the inflaton is a pseudo-scalar axion, the axion shift symmetry can protect the flatness of its potential from too large radiative corrections. This possibility, known as natural inflation, requires an axion scale which is greater than the (reduced) Planck scale. It is unclear whether such a high value is compatible with an effective field theoretical description, and if the global axionic symmetry survives quantum gravity effects. We propose a mechanism which provides an effective large axion scale, although the original one is sub-Planckian. The mechanism is based on the presence of two axions, with a potential provided by two anomalous gauge groups. The effective large axion scale is due to an almost exact symmetry between the couplings of the axions to the anomalous groups. We also comment on a possible implementation in heterotic string theory.
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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.
Multi-axion models relax the E/N bound on QCD axion photon coupling and allow subdominant dark matter contribution, but an axion-like particle is typically visible to next-generation experiments.
Combining periodic non-minimal couplings to the Nieh-Yan term and Ricci scalar in metric-affine gravity makes natural inflation viable for sub-Planckian periodicity scales.
The paper verifies the bound fS/|n| ≤ (π/(2 κ_d)) sqrt((d-1)/(d-2)) for axion instantons and sharpens it to fS/|n| ≤ (1/κ_4) sqrt(7/2) for supersymmetric 4d instantons using three approaches in the string landscape.
Photon-axion conversion near Kerr black holes produces dimming of photon spectral luminosity that increases with black hole spin, magnetic field strength, and photon-axion coupling, most efficiently at high frequencies.
Tera-Z factories can produce millions of heavy neutral leptons and billions of axion-like particles under optimistic assumptions, turning them into exotics factories for discovery and detailed study.
Non-Bunch-Davies initial conditions substantially improve the fit of various single-field slow-roll inflation models to updated n_s-r constraints from ACT DR6 combined with Planck, DESI, and BICEP/Keck data.
A review thesis covering Mukhanov parametrization, general scalar-tensor theories, and new slow-roll techniques for canonical and noncanonical inflation observables.
A roadmap paper describing potential applications of numerical Ricci-flat Calabi-Yau metrics to heterotic string phenomenology and mathematical questions in special geometry.
Review classifies QCD axion models extending the standard mass-coupling window and updates bounds from cosmology, astrophysics, and experiments.
citing papers explorer
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Natural Metric-Affine Inflation: Reloaded
Combining periodic non-minimal couplings to the Nieh-Yan term and Ricci scalar in metric-affine gravity makes natural inflation viable for sub-Planckian periodicity scales.
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Dimming of Photon Ring due to Photon-Axion Conversion around Kerr Black Holes
Photon-axion conversion near Kerr black holes produces dimming of photon spectral luminosity that increases with black hole spin, magnetic field strength, and photon-axion coupling, most efficiently at high frequencies.
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Noncanonical Approaches To Inflation
A review thesis covering Mukhanov parametrization, general scalar-tensor theories, and new slow-roll techniques for canonical and noncanonical inflation observables.