Generic 2D Horndeski theories arise from dimensional reduction of d≥4 gravities, yielding a Birkhoff theorem for quasi-topological gravities where static spherically symmetric solutions satisfy g_tt g_rr = -1 and are determined algebraically.
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GRAVITY AND GLOBAL SYMMETRIES
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abstract
There exists a widely spread notion that gravitational effects can strongly violate global symmetries. It may lead to many important consequences. We will argue, in particular, that nonperturbative gravitational effects in the axion theory lead to a strong violation of CP invariance unless they are suppressed by an extremely small factor 10^{-82}. One could hope that this problem disappears if one represents the global symmetry of a pseudoscalar axion field as a gauge symmetry of the Ogievetsky-Polubarinov-Kalb-Ramond antisymmetric tensor field. We will show, however, that this gauge symmetry does not protect the axion mass from quantum corrections. The amplitude of gravitational effects violating global symmetries could be strongly suppressed by e^{-S}, where S is the action of a wormhole which may eat the global charge. Unfortunately, in a wide variety of theories based on the Einstein theory of gravity the action appears to be fairly small, S = O(10). However, we have found that the existence of wormholes and the value of their action are extremely sensitive to the structure of space on the nearly Planckian scale. We consider several examples (Kaluza-Klein theory, conformal anomaly, R^2 terms) which show that modifications of the Einstein theory on the length scale l ~ 10 M_P^{-1} may strongly suppress violation of global symmetries. We have found also that in string theory there exists an additional suppression of topology change by the factor e^{-{8\pi^2\over g^2}}. This effect is strong enough to save the axion theory for the natural values of the stringy gauge coupling constant.
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Positivity of gravitational path integral inner products requires non-perturbative instabilities in axion wormholes that break shift symmetry, implying a sharp axion weak gravity conjecture with precise constants.
Defects tied to discrete symmetries via bordism groups Ω^ξ_2(BG) and homology H_2(BG;Z) are codimension-two branes that participate in networks with junctions, expanding the Cobordism Conjecture's predictions in string-derived supergravity.
Proposes a refinement of the Swampland Cobordism Conjecture for Ω1(BG) with duality bundle G, where diverging commutator width of G requires infinitely many duality defects to realize monodromies via gravitational solitons.
An 't Hooft anomaly at general imaginary baryon chemical potential constrains the QCD chiral transition to three minimal CFT scenarios, with the favored one for N_f >= 3 featuring a conformal manifold of theta_B-dependent universality classes with an exactly marginal operator tied to baryon density.
In asymptotically safe gravity, dimension-five couplings of ultralight scalar dark matter to gauge field strengths vanish and are not generated perturbatively.
Morse-Bott inequalities yield homology bounds and topology-change counts for generic cobordisms to nothing in string theory compactifications.
Special embedding of the composite axion and QCD gauge groups into a larger product gauge group reduces the domain wall number to unity and induces a controlled bias term from UV instantons that destabilizes the walls.
A chiral U(1) gauge symmetry generates an accidental Peccei-Quinn symmetry broken by mirror QCD, solving the strong CP problem without a light axion while supplying WIMP dark matter, stochastic gravitational waves, and LHC-testable colored pNGBs.
In gauged U(1) completions enabling high-quality axion dark matter, cosmic string loops generate a stochastic gravitational wave background with an infrared break frequency that exceeds foregrounds above 10^14 GeV breaking scales and offers a probe at interferometers.
Spontaneous wash-in leptogenesis in Type II Seesaw with Majoron pNGB background enables baryon asymmetry generation alongside dark matter cogenesis for specific v_T, v_sigma and m_j ranges.
Six classes of CP-violating operators near the QCD scale produce distinct EDM patterns that enable discrimination of their origins and distinguish high-scale versus low-energy sources of the axion vacuum expectation value.
Kinetic mixing between hidden-sector fluxes and QCD's topological sector shifts the effective theta angle and produces nonzero <G tilde G>.
High-quality axion models with N_DW=1 and dark matter abundance requirement restrict the gauge breaking scale to 1.6e11-1e16 GeV, yielding a band of gravitational wave signals from two-step phase transitions consistent with current observations.
Review classifies QCD axion models extending the standard mass-coupling window and updates bounds from cosmology, astrophysics, and experiments.
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All $2D$ generalised dilaton theories from $d\geq 4$ gravities
Generic 2D Horndeski theories arise from dimensional reduction of d≥4 gravities, yielding a Birkhoff theorem for quasi-topological gravities where static spherically symmetric solutions satisfy g_tt g_rr = -1 and are determined algebraically.
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Positivity of the gravitational path integral implies the axionic weak gravity conjecture
Positivity of gravitational path integral inner products requires non-perturbative instabilities in axion wormholes that break shift symmetry, implying a sharp axion weak gravity conjecture with precise constants.
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A missing link: Brane networks and the Cobordism Conjecture
Defects tied to discrete symmetries via bordism groups Ω^ξ_2(BG) and homology H_2(BG;Z) are codimension-two branes that participate in networks with junctions, expanding the Cobordism Conjecture's predictions in string-derived supergravity.
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Bordisms between 9d type IIB supergravities and commutator widths of duality groups
Proposes a refinement of the Swampland Cobordism Conjecture for Ω1(BG) with duality bundle G, where diverging commutator width of G requires infinitely many duality defects to realize monodromies via gravitational solitons.
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Does hot QCD have a conformal manifold in the chiral limit?
An 't Hooft anomaly at general imaginary baryon chemical potential constrains the QCD chiral transition to three minimal CFT scenarios, with the favored one for N_f >= 3 featuring a conformal manifold of theta_B-dependent universality classes with an exactly marginal operator tied to baryon density.
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Towards theory constraints on ultralight dark matter from quantum gravity
In asymptotically safe gravity, dimension-five couplings of ultralight scalar dark matter to gauge field strengths vanish and are not generated perturbatively.
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Morse-Bott inequalities, Topology Change and Cobordisms to Nothing
Morse-Bott inequalities yield homology bounds and topology-change counts for generic cobordisms to nothing in string theory compactifications.
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Specially Embedding a Composite Axion Model
Special embedding of the composite axion and QCD gauge groups into a larger product gauge group reduces the domain wall number to unity and induces a controlled bias term from UV instantons that destabilizes the walls.
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Accidental Peccei-Quinn Symmetry from Chiral Gauge Symmetry and Mirror QCD
A chiral U(1) gauge symmetry generates an accidental Peccei-Quinn symmetry broken by mirror QCD, solving the strong CP problem without a light axion while supplying WIMP dark matter, stochastic gravitational waves, and LHC-testable colored pNGBs.
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High-Quality Axion Dark Matter at Gravitational Wave Interferometers
In gauged U(1) completions enabling high-quality axion dark matter, cosmic string loops generate a stochastic gravitational wave background with an infrared break frequency that exceeds foregrounds above 10^14 GeV breaking scales and offers a probe at interferometers.
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Type II Seesaw Leptogenesis in a Majoron background
Spontaneous wash-in leptogenesis in Type II Seesaw with Majoron pNGB background enables baryon asymmetry generation alongside dark matter cogenesis for specific v_T, v_sigma and m_j ranges.
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The EDM inverse problem: Identifying the sources of CP violation and PQ breaking with electric dipole moments
Six classes of CP-violating operators near the QCD scale produce distinct EDM patterns that enable discrimination of their origins and distinguish high-scale versus low-energy sources of the axion vacuum expectation value.
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Flux Mixing and CP Violation in QCD
Kinetic mixing between hidden-sector fluxes and QCD's topological sector shifts the effective theta angle and produces nonzero <G tilde G>.
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Probing High-Quality Axions with Gravitational Waves
High-quality axion models with N_DW=1 and dark matter abundance requirement restrict the gauge breaking scale to 1.6e11-1e16 GeV, yielding a band of gravitational wave signals from two-step phase transitions consistent with current observations.
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The landscape of QCD axion models
Review classifies QCD axion models extending the standard mass-coupling window and updates bounds from cosmology, astrophysics, and experiments.
- Axion Quality in Warped Extra-Dimension