Infinite-derivative completions of quasitopological gravities are ghost-free, avoid strong coupling, and admit exact spherically symmetric vacuum regular black holes obeying a perturbative Birkhoff theorem.
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Towards singularity and ghost free theories of gravity
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We present the most general covariant ghost-free gravitational action in a Minkowski vacuum. Apart from the much studied f(R) models, this includes a large class of non-local actions with improved UV behavior, which nevertheless recover Einstein's general relativity in the IR.
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Non-singular gravity with regulator ℓ induces a PBH mass gap ~c²ℓ/G and a stronger Carr criterion δ_H > 2GM_gap/R_H - 1 when R_H ~ ℓ.
Fractional gravity yields stable de Sitter expansion and exact bouncing solutions driven by phantom (w < -1) or ghost (negative energy) fluids, with results independent of the form-factor representation.
A ghost-free polynomially bounded scalar theory with momentum-dependent interactions that cancels all loop divergences to all orders, with finite one-loop self-energy and beta function computed, plus a variant with zero mass renormalization.
At quadratic order in asymptotically safe gravity, the graviton propagator has a single pole at q²=0 with positive residue, no ghost poles, and yields a regular Newtonian potential at r=0.
Asymptotically safe gravitational form factors are obtained by integrating the proper-time flow to k=0; finite cutoff-independent results with 1/q² UV decay require selecting the non-Gaussian fixed point as UV boundary condition.
Specific choices of form factors in ghost-free infinite derivative gravity cancel all one-loop logarithmic UV divergences except the Gauss-Bonnet term and a surface term.
A PPT witness criterion is proposed to detect graviton-mediated entanglement between photons and matter qubits, attaining a maximal negativity of -0.052 for non-maximally entangled states when the photon coherent-state overlap satisfies 0.71 ≤ |γ| < 1.
Fractional powers in QFT kinetic terms can be consistently formulated in Minkowski space using fakeon methods, yielding multiple inequivalent theories that match in Euclidean space, with standard identities preserved.
In symmetric teleparallel f(Q) gravity with nonminimal EM-nonmetricity coupling, the distance duality relation is dynamically violated, yielding a generalized formula relating observational distances to the Hubble rate.
Virtual graviton exchange between a photon and a high-spinning quantum rotor generates entanglement between photon degrees of freedom and rotor position, with prograde-retrograde motion yielding observable differences in linear entanglement entropy.
Generalized hybrid metric-Palatini gravity propagates a massless spin-2 mode and two massive scalars in the weak field; stability requires algebraic conditions on f derivatives at flat space, and planetary data constrain the scalar masses in a hierarchical regime.
Higher-order curvature operators like R□R add new poles and shift existing ones in the graviton propagator, with a method to correctly derive the Einstein frame action illustrated for f(R) gravity.
A matter-wave interferometer with a Schrödinger cat state displaces the graviton vacuum into coherent states, with the left-right overlap providing a gravitational contrast that quantifies entanglement between matter and the quantized gravitational field.
If Hawking's area law is taken as exact, nonlocal and Stelle quantum-gravity theories are forced to drop R^2 and (Riemann)^2 terms (or use singular Ricci-flat black holes), and the standard entropy-area law follows as a consequence.
Nonlocal form factors in D-dimensional gravity yield effective geometries whose nonlinear completion gives regular, asymptotically flat Schwarzschild deformations with de Sitter cores.
The paper derives a nonlocal phase-space uncertainty relation implying a minimal measurable length of order L_M and a finite phase-space cell in nonlocal QFT.
Causality is a misleading metaphysical concept that should be abandoned in fundamental physics, making renouncing microcausality acceptable for consistent quantum gravity theories such as those using fakeons.
A review summarizing modified theories of gravity, their effects on compact objects, existing bounds from astrophysical observations, and the promise of future gravitational wave tests for strong-field gravity.
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Infinite-derivative completions of quasitopological gravities are ghost-free, avoid strong coupling, and admit exact spherically symmetric vacuum regular black holes obeying a perturbative Birkhoff theorem.
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Non-singular gravity with regulator ℓ induces a PBH mass gap ~c²ℓ/G and a stronger Carr criterion δ_H > 2GM_gap/R_H - 1 when R_H ~ ℓ.
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The Graviton Propagator in Asymptotically Safe Gravity with Non-Local Form Factors
At quadratic order in asymptotically safe gravity, the graviton propagator has a single pole at q²=0 with positive residue, no ghost poles, and yields a regular Newtonian potential at r=0.
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Asymptotically Safe Gravitational Form Factors from the Proper-Time Flow Equation
Asymptotically safe gravitational form factors are obtained by integrating the proper-time flow to k=0; finite cutoff-independent results with 1/q² UV decay require selecting the non-Gaussian fixed point as UV boundary condition.
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Cancellation of UV divergences in ghost-free infinite derivative gravity
Specific choices of form factors in ghost-free infinite derivative gravity cancel all one-loop logarithmic UV divergences except the Gauss-Bonnet term and a surface term.
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Witnessing entanglement between photon and matter due to graviton exchange
A PPT witness criterion is proposed to detect graviton-mediated entanglement between photons and matter qubits, attaining a maximal negativity of -0.052 for non-maximally entangled states when the photon coherent-state overlap satisfies 0.71 ≤ |γ| < 1.
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Fractions and Fakeons in Quantum Field Theory
Fractional powers in QFT kinetic terms can be consistently formulated in Minkowski space using fakeon methods, yielding multiple inequivalent theories that match in Euclidean space, with standard identities preserved.
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Distance duality relation in symmetric teleparallel gravity
In symmetric teleparallel f(Q) gravity with nonminimal EM-nonmetricity coupling, the distance duality relation is dynamically violated, yielding a generalized formula relating observational distances to the Hubble rate.
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Graviton-mediated entanglement due to light bending from a quantum rotor
Virtual graviton exchange between a photon and a high-spinning quantum rotor generates entanglement between photon degrees of freedom and rotor position, with prograde-retrograde motion yielding observable differences in linear entanglement entropy.
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Another Look at the Weak-Field Limit of Generalized Hybrid Metric-Palatini Gravity
Generalized hybrid metric-Palatini gravity propagates a massless spin-2 mode and two massive scalars in the weak field; stability requires algebraic conditions on f derivatives at flat space, and planetary data constrain the scalar masses in a hierarchical regime.
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The Spectrum of Quantum Gravity
Higher-order curvature operators like R□R add new poles and shift existing ones in the graviton propagator, with a method to correctly derive the Einstein frame action illustrated for f(R) gravity.
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Quantum gravitational contrast in creating Schr\"odinger cat state
A matter-wave interferometer with a Schrödinger cat state displaces the graviton vacuum into coherent states, with the left-right overlap providing a gravitational contrast that quantifies entanglement between matter and the quantized gravitational field.
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Hawking area law in quantum gravity
If Hawking's area law is taken as exact, nonlocal and Stelle quantum-gravity theories are forced to drop R^2 and (Riemann)^2 terms (or use singular Ricci-flat black holes), and the standard entropy-area law follows as a consequence.
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Eikonal, nonlocality and regular black holes
Nonlocal form factors in D-dimensional gravity yield effective geometries whose nonlinear completion gives regular, asymptotically flat Schwarzschild deformations with de Sitter cores.
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On the Meaning of Localization in Non-Local Quantum Field Theory and On the Limits of a Space-Time Description and the Physical Meaning of Phase Space in a Nonlocal Continuum
The paper derives a nonlocal phase-space uncertainty relation implying a minimal measurable length of order L_M and a finite phase-space cell in nonlocal QFT.
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On Causality and Predictivity
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Testing General Relativity with Present and Future Astrophysical Observations
A review summarizing modified theories of gravity, their effects on compact objects, existing bounds from astrophysical observations, and the promise of future gravitational wave tests for strong-field gravity.