The Strong CP Problem

The paper defines the QFT path integral using only perturbative boundary conditions and asserts, without a valid proof, that this removes all non-perturbative effects.

arxiv:2412.11246 · physics.gen-ph · 2024-12

A spontaneously broken modular CP symmetry can force the quark mass determinant to be real, solving the strong CP problem without an axion.

arxiv:2501.16427 · hep-ph · 2025-01

In a quantum rotor with a topological term, the proposed order of limits predicts zero topological susceptibility, contradicting both the exact quantum mechanical result and lattice simulations.

arxiv:2502.01217 · hep-lat · 2025-02

For Z_4^R and Z_8^R discrete R-symmetries, R-parity violating couplings of order 10^-7 make the lightest supersymmetric particle decay in 10^-3 to 10 seconds, so the dark matter is entirely axion cold dark matter.

arxiv:2502.06955 · hep-ph · 2025-02

Modular invariance can suppress the QCD theta angle to zero in string-inspired supersymmetric models with positive modular weights and non-trivial gauge kinetic functions, while the CKM phase stays large.

arxiv:2505.20395 · hep-ph · 2025-05

Derivative-coupled gravitational axions cannot solve the strong CP problem; Weyl-invariant Einstein-Cartan gravity is identified as the only promising framework for a gravitational QCD axion.

arxiv:2506.11836 · hep-th · 2025-06

A review of Weyl-invariant Einstein-Cartan gravity claiming that one extra axion-like scalar can unify the strong CP and hierarchy puzzles, with the hierarchy explained by tiny Lorentz gauge couplings.

arxiv:2506.11847 · hep-th · 2025-06

In a supersymmetric Twin Higgs model, light scalars can keep electroweak symmetry broken at high temperature, and a special neutrino sector can suppress dark radiation to match CMB limits.

arxiv:2508.15894 · hep-ph · 2025-08

Leptogenesis can proceed from single-generation gauge-singlet mediator decays in a Universal Seesaw model if parity is broken in the neutrino sector; the lightest right-handed neutrino is a sub-eV dark-radiation relic.

arxiv:2512.19833 · hep-ph · 2025-12

Maximally invisible QCD axions, interacting only via gluons, yield SN 1987A cooling constraints and Cherenkov signals that establish a robust lower bound on QCD axion detectability.

arxiv:2607.12025 · hep-ph · 2026-07

The conventional strong CP problem is contingent on extra global topological assumptions about gauge fields that no established QCD observable is shown to require.

arxiv:2607.10272 · hep-ph · 2026-07

Warped extra-dimensional Wilson-line axions can achieve high quality when non-QCD potential contributions from charged bulk fields are parametrically suppressed by geometry and brane effects.

arxiv:2604.08700 · hep-ph · 2026-04

MeV-scale dark QCD with mixed U(1)_PQ anomaly lifts Z_NDW degeneracy of axion domain walls while preserving the strong-CP solution, yielding PTA-accessible GWs and MeV di-photon signals.

arxiv:2607.04137 · hep-ph · 2026-07

Anomaly-free discrete R-symmetries plus Kim-Nilles regeneration of the mu term force an accidental U(1)_PQ whose spontaneous breaking yields a SUSY DFSZ axion that solves strong CP.

arxiv:2607.07921 · hep-ph · 2026-07

Models with Peccei-Quinn symmetry and vector-like quarks realize one-loop proton decay through the operator u_R u_R d_R e_R while preserving a residual Z2 that forbids tree-level decay, yielding testable axion-photon couplings and an axion-accompanied decay mode.

arxiv:2607.02026 · hep-ph · 2026-07

Multi-axion solutions to the strong CP problem produce varied mass-coupling patterns set by PQ symmetry breaking structure and QCD-EM anomaly alignment, summarized by a general sum rule for N-axion systems.

arxiv:2605.06787 · hep-ph · 2026-05

A mirror GUT model confines dynamically to produce a heavy axion solving the strong CP problem while allowing observable EDMs and a rich hidden sector.

arxiv:2605.28954 · hep-ph · 2026-05

Big axions are axion models from collective spontaneous breaking of a delocalized network of U(1) symmetries that realize high-quality accidental global symmetries, solve the strong CP problem, and may explain dark matter.

arxiv:2606.05276 · hep-ph · 2026-06

A review summarizing theoretical foundations for spin-dependent interactions mediated by ALPs and current experimental constraints on them.

arxiv:2606.13318 · hep-ph · 2026-06

A review of progress in quantifying flavor-diagonal hadronic CP violation effects on EDMs, neutron optics, beta decay, and an attempt to address the strong CP problem without new fields or interactions.

arxiv:2606.23580 · hep-ph · 2026-06

CP conservation in QCD follows from taking the infinite volume limit prior to summing over topological sectors, shown consistent with steepest-descent contours and chiral EFT.

arxiv:2404.16026 · hep-ph · 2024-04

In a parity-symmetric model with TeV-scale lepton number violation, a 10 TeV μ+μ+ collider can probe W' boson masses up to 16 TeV via on-shell and off-shell lepton number violating production.

arxiv:2509.24680 · hep-ph · 2025-09

Type IIA orientifold model with D6-branes stabilizes moduli via STU and KL, predicts axion-neutralino dark matter, and uses four-form flux to address strong CP problem.

arxiv:2603.18566 · hep-th · 2026-03

Dynamical generation of leptonic CP violation and light sterile neutrino masses via radiative breaking of non-invertible selection rules, illustrated in the Inverse Seesaw model.

arxiv:2604.04423 · hep-ph · 2026-04

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.

arxiv:2604.24849 · hep-ph · 2026-04

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.

arxiv:2604.26010 · hep-ph · 2026-04