Bob Holdom

Flavor changing suppression in technicolor

Abstract ΔS = 2 effects are suppressed by a factor ( α w 2π ) 2 ϑ 2 C while allowing for Cabibbo mixing. A model realizing this mechanism has no severe flavor changing problems. μ → e γ is suppressed while K → e + μ − is not. Charged pseudo-Goldstone masses are first order rather than second order in the weak coupling. And there are two stable pseudo-Goldstone bosons.

Not quite a black hole

Astrophysical black hole candidates, although long thought to have a horizon, could be horizonless ultracompact objects. This intriguing possibility is motivated by the black hole information paradox and a plausible fundamental connection with quantum gravity. Asymptotically free quadratic gravity is considered here as the UV completion of general relativity. A classical theory that captures its main features is used to search for solutions as sourced by matter. We find that sufficiently dense matter produces a novel horizonless configuration, the 2-2-hole, which closely matches the exterior Schwarzschild solution down to about a Planck proper length of the would-be horizon. The 2-2-hole is characterized by an interior with a shrinking volume and a seemingly innocuous timelike curvature singularity. The interior also has a novel scaling behavior with respect to the physical mass of the 2-2-hole. This leads to an extremely deep gravitational potential in which particles get efficiently trapped via collisions. As a generic static solution, the 2-2-hole may then be the nearly black end point of gravitational collapse. There is a considerable time delay for external probes of the 2-2-hole interior, and this determines the spacing of echoes in a postmerger gravitational wave signal.

Raising the axion mass

We present a mechanism which raises the axion mass while maintaining the standard axion-fermion coupling and the removal of strong CP violation. The source of this new contribution to the axion mass is small color SU(3) instantins; these may be important if new physics above the weak interaction scale causes the color coupling constant to grow strong and produces anomalous dimensions for certain many-fermion operators. Strongly interacting hyperquarks may be responsible for both effects. We discuss the working of this mechanism in an explicit hypercolor-sideways interaction model in which a Peccei-Quinn symmetry appears naturally. In this particular model, heavy axion exchange could produce significant DODO mixing.

Monopoles, strings, and dark matter

We develop a scenario whereby monopoles in a hidden sector yield a decaying dark matter candidate of interest for the PAMELA and FERMI

Gauged fermions from tensor fields

e^\pm

Heavy Higgs decay to

excesses. The monopoles are not completely hidden due to a very small kinetic mixing and a hidden photon mass. The latter also causes the monopoles and anti-monopoles to be connected by strings. The resulting long-lived objects eventually decay to hidden photons which tend to escape galactic cores before decaying. The mass scales are those of the hidden photon (

t\bar{t} Z

\approx 500

and constraints on a

MeV), the monopole (

750

\approx 3

GeV pseudoscalar

TeV) and the mixing scale (close to the Planck scale). A gauge coupling in the hidden sector is the only other parameter. This coupling must be strong and this results in light point-like monopoles and light thin strings.