Sign-switching dark energy with a transition at z_† fits recent DESI DR2, Planck CMB, and Pantheon+ data better than ΛCDM while raising the inferred Hubble constant and easing the Hubble tension.
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Dark energy from the string axiverse
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abstract
String theories suggest the existence of a plethora of axion-like fields with masses spread over a huge number of decades. Here we show that these ideas lend themselves to a model of quintessence with no super-Planckian field excursions and in which all dimensionless numbers are order unity. The scenario addresses the "why now" problem, i.e., why has accelerated expansion begun only recently, by suggesting that the onset of dark-energy domination occurs randomly with a slowly decreasing probability per unit logarithmic interval in cosmic time. The standard axion potential requires us to postulate a rapid decay of most of the axion fields that do no become dark energy. The need for these decays is averted, though, with the introduction of a slightly modified axion potential. In either case, a Universe like ours arises in roughly 1 in 100 universes. The scenario may have a host of observable consequences.
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Computes 1PN conservative dynamics for gravitational/EM/Proca fields and 2PN for scalar, plus radiation effects from axion-photon coupling at high PN orders in binary black hole systems with dark matter.
An analytic bound on axion parameters in thawing quintessence is derived independently of initial conditions and used with cosmological observations plus quantum gravity constraints to exclude large regions of axion dark energy parameter space.
QCD axions constrain F-theory base threefolds to have rigid or flux-rigidified divisors, yielding typical axion masses around 10^{-9} eV and decay constants near 10^{15} GeV in allowed regions.
The Hubble tension between local and early-universe expansion-rate measurements may be resolved by early dark energy that speeds up expansion before recombination while satisfying existing constraints.
A review summarizing the Hubble constant tension and proposed solutions from new physics that restore agreement between Planck CMB data and local H0 measurements within 1-2 sigma.
citing papers explorer
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Sign-Switching Dark Energy: Smooth Transitions with Recent DESI DR2 Observations
Sign-switching dark energy with a transition at z_† fits recent DESI DR2, Planck CMB, and Pantheon+ data better than ΛCDM while raising the inferred Hubble constant and easing the Hubble tension.
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Worldline effective field theory of inspiralling black hole binaries in presence of dark photon and axionic dark matter
Computes 1PN conservative dynamics for gravitational/EM/Proca fields and 2PN for scalar, plus radiation effects from axion-photon coupling at high PN orders in binary black hole systems with dark matter.
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Bounding axion dark energy
An analytic bound on axion parameters in thawing quintessence is derived independently of initial conditions and used with cosmological observations plus quantum gravity constraints to exclude large regions of axion dark energy parameter space.
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Constraining F-theory Model Building with QCD Axions
QCD axions constrain F-theory base threefolds to have rigid or flux-rigidified divisors, yielding typical axion masses around 10^{-9} eV and decay constants near 10^{15} GeV in allowed regions.
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The Hubble Tension and Early Dark Energy
The Hubble tension between local and early-universe expansion-rate measurements may be resolved by early dark energy that speeds up expansion before recombination while satisfying existing constraints.
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In the Realm of the Hubble tension $-$ a Review of Solutions
A review summarizing the Hubble constant tension and proposed solutions from new physics that restore agreement between Planck CMB data and local H0 measurements within 1-2 sigma.