Several Problems in Particle Physics and Cosmology Solved in One SMASH

Abstract

The Standard Model (SM) of particle physics is a big success. However, it lacks explanations for cosmic inflation, the matter-anti-matter asymmetry of the Universe, dark matter, neutrino oscillations, and the feebleness of CP violation in the strong interactions. The latter may be explained by a complex scalar field charged under a spontaneously broken global U(1) Peccei-Quinn (PQ) symmetry. Moreover, the pseudo Nambu-Goldstone boson of this breaking -the axion-may play the role of the dark matter. Furthermore, the modulus of the PQ field is a candidate for driving inflation. If additionally three extra SM singlet neutrinos (whose mass is induced by the PQ field) are included, the five aforementioned problems can be addressed at once. We review the SM extension dubbed SMASH -for SM-Axion-Seesaw-Higgs portal inflation-, discuss its predictions and tests in astrophysics, cosmology, and laboratory experiments. Variants of SMASH are also considered and commented on.

The landscape of QCD axion models

“…For example, in the unified Standard Model-Axion-seesaw-Higgs portal inflation (SMASH) model of Refs. [283][284][285], although the axion energy scale can be as large as f a ∼ 4 × 10 16 GeV, the PQ symmetry is restored immediately after the end of inflation and isocurvature modes are absent. Caveats that allow to evade the bound from isocurvature fluctuations include the presence of more than one axion [286], or the identification of the inflaton with the radial component of the PQ field [287], see Section 7.3.…”

“…A non-trivial step in this direction was achieved recently, in the context of the Standard Model-Axion-Seesaw-Higgs inflation portal (SMASH) model [283][284][285], in which the modulus of the PQ scalar is also the key ingredient for successful inflation. A robust prediction of this setup is that the PQ symmetry is broken after inflation and never restored after it, thus making the range for axion DM in principle calculable.…”

“…For this reason, a non-minimal coupling to gravity ξ is introduced to circumvent the bounds from the Planck mission, so that the potential at large values of ρ a is flattened out and the model reconciles with observations [660]. A different kind of embedding has been carried out in the SMASH model [283][284][285], in which the Lagrangian (in the Jordan frame) contains a term which elaborates over the Higgs inflation model [661] to include a mixture of the PQ complex multiplet Φ and of the Higgs field doublet H,…”

Elementary Particles, Dark Matter, and Dark Energy: Descriptions that Explain Aspects of Dark Matter to Ordinary Matter Ratios, Inflation, Early Galaxies, and Expansion of the Universe

“…Proposed theory tries to address topics that ongoing theory tries to address. (For example, reference [1] provides an ongoing theory attempt to address topics that proposed theory tries to address.) is mathematics that underlies theories or models.…”

“…• We posit that equations (6) and (7) extend equation (1). Here, the applicable number, n, of excitations satisfies n ≥ 0.…”