A new covariant foliation-based construction of scalar-tensor theories up to four derivatives of the scalar field that extends DHOST and U-DHOST without unitary gauge and propagates three degrees of freedom.
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Arkani-Hamed, H.-C
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abstract
We propose a theoretically consistent modification of gravity in the infrared, which is compatible with all current experimental observations. This is an analog of Higgs mechanism in general relativity, and can be thought of as arising from ghost condensation--a background where a scalar field \phi has a constant velocity, <\dot\phi> = M^2. The ghost condensate is a new kind of fluid that can fill the universe, which has the same equation of state, \rho = -p, as a cosmological constant, and can hence drive de Sitter expansion of the universe. However, unlike a cosmological constant, it is a physical fluid with a physical scalar excitation, which can be described by a systematic effective field theory at low energies. The excitation has an unusual low-energy dispersion relation \omega^2 \sim k^4 / M^2. If coupled to matter directly, it gives rise to small Lorentz-violating effects and a new long-range 1/r^2 spin dependent force. In the ghost condensate, the energy that gravitates is not the same as the particle physics energy, leading to the possibility of both sources that can gravitate and antigravitate. The Newtonian potential is modified with an oscillatory behavior starting at the distance scale M_{Pl}/M^2 and the time scale M_{Pl}^2/M^3. This theory opens up a number of new avenues for attacking cosmological problems, including inflation, dark matter and dark energy.
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Phase-resolved scalar distance bounds are derived for ekpyrotic, bouncing, and cyclic cosmologies, yielding a master condition that lower-bounds ε_ek from remaining distance after conversion and bounce.
Exact non-singular black holes from the phantom DBI field evaporate to gram-mass relics, opening a new mass window for primordial black holes as dark matter.
Requiring stealth Schwarzschild and de Sitter solutions in quadratic/cubic scalar-tensor theories eliminates odd-parity deviations from GR when all solutions are required, while allowing some deviations and non-trivial GW speeds in less restrictive cases.
A master screening equation is derived for luminal Horndeski gravity that recovers Vainshtein and Chameleon mechanisms and introduces Phaedrus screening with screening radius scaling linearly with source mass.
Non-relativistic propagation of a tilted-ghost spectator field during inflation produces boostless cosmological collider non-Gaussianity via an effective chemical-potential-like tilt parameter.
The degeneracy of the constraint structure at nontrivial magnetic vacua follows from the constitutive origin of the effective Hamiltonian as complementary energy at fixed D.
Higher-curvature terms deform the near-horizon potential of spherically symmetric black holes, producing progressively larger shifts in overtone quasinormal frequencies that remain detectable in ringdown waveforms when the fundamental mode stays close to its GR value.
Five explicit polynomial spatially covariant gravity Lagrangians up to total derivative order three are identified that propagate only two degrees of freedom up to cubic order in perturbations around a cosmological background.
Interacting k-essence dark energy and non-pressureless dark matter models with two interaction forms are shown to reproduce major cosmological epochs and fit observations comparably to LambdaCDM while admitting late-time de Sitter attractors.
Interacting scalar fields coupled to Gauss-Bonnet gravity yield viable dark energy and dark matter models that match Pantheon+ and DES supernova data while preferring over LambdaCDM at high redshifts with Roman mocks.
Cosmic string networks are constrained to less than ~1% of the energy density using CMB+BAO+SN data, with some models preferring mildly negative densities but no Bayesian evidence favoring them over LambdaCDM.
citing papers explorer
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Covariant scalar-tensor theories beyond second derivatives
A new covariant foliation-based construction of scalar-tensor theories up to four derivatives of the scalar field that extends DHOST and U-DHOST without unitary gauge and propagates three degrees of freedom.
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Phase-resolved field-space distance bounds in ekpyrotic, bouncing and cyclic cosmologies
Phase-resolved scalar distance bounds are derived for ekpyrotic, bouncing, and cyclic cosmologies, yielding a master condition that lower-bounds ε_ek from remaining distance after conversion and bounce.
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Exact, non-singular black holes from a phantom DBI Field as primordial dark matter
Exact non-singular black holes from the phantom DBI field evaporate to gram-mass relics, opening a new mass window for primordial black holes as dark matter.
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Inverting no-hair theorems: How requiring General Relativity solutions restricts scalar-tensor theories
Requiring stealth Schwarzschild and de Sitter solutions in quadratic/cubic scalar-tensor theories eliminates odd-parity deviations from GR when all solutions are required, while allowing some deviations and non-trivial GW speeds in less restrictive cases.
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A Master Equation for Screening in Luminal Horndeski Gravity
A master screening equation is derived for luminal Horndeski gravity that recovers Vainshtein and Chameleon mechanisms and introduces Phaedrus screening with screening radius scaling linearly with source mass.
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Non-Relativistic Cosmological Collider Signals
Non-relativistic propagation of a tilted-ghost spectator field during inflation produces boostless cosmological collider non-Gaussianity via an effective chemical-potential-like tilt parameter.
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Constitutive Origin of Hamiltonian Degeneracy in Nonlinear Electrodynamics with Spontaneous Lorentz Symmetry Breaking
The degeneracy of the constraint structure at nontrivial magnetic vacua follows from the constitutive origin of the effective Hamiltonian as complementary energy at fixed D.
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Probing higher curvature gravity via ringdown with overtones
Higher-curvature terms deform the near-horizon potential of spherically symmetric black holes, producing progressively larger shifts in overtone quasinormal frequencies that remain detectable in ringdown waveforms when the fundamental mode stays close to its GR value.
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Spatially covariant gravity with two degrees of freedom: A perturbative analysis up to cubic order
Five explicit polynomial spatially covariant gravity Lagrangians up to total derivative order three are identified that propagate only two degrees of freedom up to cubic order in perturbations around a cosmological background.
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Interacting $k$-essence field with non-pressureless Dark Matter: Cosmological Dynamics and Observational Constraints
Interacting k-essence dark energy and non-pressureless dark matter models with two interaction forms are shown to reproduce major cosmological epochs and fit observations comparably to LambdaCDM while admitting late-time de Sitter attractors.
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Interacting Scalar Fields as Dark Energy and Dark Matter in Einstein scalar Gauss Bonnet Gravity
Interacting scalar fields coupled to Gauss-Bonnet gravity yield viable dark energy and dark matter models that match Pantheon+ and DES supernova data while preferring over LambdaCDM at high redshifts with Roman mocks.
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Cosmic Strings as Dynamical Dark Energy: Novel Constraints
Cosmic string networks are constrained to less than ~1% of the energy density using CMB+BAO+SN data, with some models preferring mildly negative densities but no Bayesian evidence favoring them over LambdaCDM.