String theory predicts an axiverse of ultralight axions whose effects on CMB polarization, matter power spectrum, and black hole superradiance can be probed by future astrophysical experiments.
Theta Dependence In The Large N Limit Of Four-Dimensional Gauge Theories
7 Pith papers cite this work. Polarity classification is still indexing.
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abstract
The theta dependent of pure gauge theories in four dimensions can be studied using a duality of large N gauge theories with string theory on a certain spacetime. Via this duality, one can argue that for every theta, there are infinitely many vacua that are stable in the large N limit. The true vacuum, found by minimizing the energy in this family, is a smooth function of theta except at theta equal to pi, where it jumps. This jump is associated with spontaneous breaking of CP symmetry. Domain walls separating adjacent vacua are described in terms of wrapped sixbranes.
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Holographic confining QFTs on negative-curvature manifolds show no phase transitions with a dominant saddle, while positive-curvature cases exhibit first- and second-order transitions depending on the theory class, plus a Vafa-Witten theorem at theta zero.
A 5D holographic QCD axion model identifies bulk modes for the axion and eta prime, traces the quality problem to insufficient compositeness, and finds the physical axion mostly in the bulk gauge field when quality is high.
Holographic 5D model shows confinement critical temperature falls quadratically with vacuum angle, matches lattice QCD, and allows time-dependent theta to trigger supercooling and altered gravitational-wave spectra.
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.
Kinetic mixing between hidden-sector fluxes and QCD's topological sector shifts the effective theta angle and produces nonzero <G tilde G>.