Weak Scale Baryogenesis in a Supersymmetric Scenario with R-parity violation

We investigate the connection between R-parity violation (RPV) in supersymmetric models and Baryogenesis. First we discuss in detail the assumptions of a theorem by Nanopoulos and Weinberg on the CP asymmetry generated from the decay of massive particles. In light of this statement, we analyse some interesting models of Baryogenesis through RPV. We then explore, in the context of RPV SUSY, the possibility to generate the baryon asymmetry through the out-of-equilibrium decay of a metastable Weakly Interacting Massive Particle (WIMP), as proposed in \cite{Cui:2012jh}. This setting is also motivated by the observed coincidence between the abundances of dark and baryonic matter. In this framework, we propose two models of out-of-equilibrium decay of a would-be cold relic, and compute the associated CP asymmetry. With a TeV-scale parent, the observed baryon abundance can be reproduced in these models when the stop is in the multi-TeV region. Furthermore, annihilation of the metastable particle into SM states must be characterised by a very weak coupling, $g\sim 10^{-2}$ and by a heavy mediator $m_{med}\sim 10$ TeV. These models can also accommodate stop masses far from the TeV scale, at the expense of weakening the explanation of the $\Omega_{B}-\Omega_{DM}$ coincidence.Comment: 31 pages, 12 figures. Revised version according to JHEP requirements: quantitative analyses added in Sec. 4, extended and revised list of refs, abstract and conclusions clarifie

Axion Monodromy and the Weak Gravity Conjecture

Axions with broken discrete shift symmetry (axion monodromy) have recently played a central role both in the discussion of inflation and the `relaxion' approach to the hierarchy problem. We suggest a very minimalist way to constrain such models by the weak gravity conjecture for domain walls: While the electric side of the conjecture is always satisfied if the cosine-oscillations of the axion potential are sufficiently small, the magnetic side imposes a cutoff, $\Lambda^3 \sim m f M_{pl}$, independent of the height of these `wiggles'. We compare our approach with the recent related proposal by Ibanez, Montero, Uranga and Valenzuela. We also discuss the non-trivial question which version, if any, of the weak gravity conjecture for domain walls should hold. In particular, we show that string compactifications with branes of different dimensions wrapped on different cycles lead to a `geometric weak gravity conjecture' relating volumes of cycles, norms of corresponding forms and the volume of the compact space. Imposing this `geometric conjecture', e.g.~on the basis of the more widely accepted weak gravity conjecture for particles, provides at least some support for the (electric and magnetic) conjecture for domain walls.Comment: 22 pages, 2 figures; v2: references added, typos corrected; v3: published version + minor clarifications on self dual flux in Sec. 3.

Tuning and Backreaction in F-term Axion Monodromy Inflation

We continue the development of axion monodromy inflation, focussing in particular on the backreaction of complex structure moduli. In our setting, the shift symmetry comes from a partial large complex structure limit of the underlying type IIB orientifold or F-theory fourfold. The coefficient of the inflaton term in the superpotential has to be tuned small to avoid conflict with Kahler moduli stabilisation. To allow such a tuning, this coefficient necessarily depends on further complex structure moduli. At large values of the inflaton field, these moduli are then in danger of backreacting too strongly. To avoid this, further tunings are necessary. In weakly coupled type IIB theory at the orientifold point, implementing these tunings appears to be difficult if not impossible. However, fourfolds or models with mobile D7-branes provide enough structural freedom. We calculate the resulting inflaton potential and study the feasibility of the overall tuning given the limited freedom of the flux landscape. Our preliminary investigations suggest that, even imposing all tuning conditions, the remaining choice of flux vacua can still be large enough for such models to provide a promising path to large-field inflation in string theory.Comment: 46 pages, 6 figures; v2: typos removed, references added; v3: references adde

Primordial Black Holes from the QCD axion

We propose a mechanism to generate Primordial Black Holes (PBHs) which is independent of cosmological inflation and occurs slightly below the QCD phase transition. Our setup relies on the collapse of long-lived string-domain wall networks and is naturally realized in QCD axion models with domain wall number $N_{DW}>1$ and Peccei-Quinn symmetry broken after inflation. In our framework, dark matter is mostly composed of axions in the meV mass range along with a small fraction, $\Omega_{\text{PBH}} \gtrsim 10^{-6} \Omega_{\text{CDM}}$ of heavy $M \sim 10^4-10^7 M_\odot$ PBHs. The latter could play a role in alleviating some of the shortcomings of the $\Lambda$CDM model on sub-galactic scales. The scenario has distinct signatures in ongoing axion searches as well as gravitational wave observatories.Comment: 7 pages, 2 figures. v2: version accepted for publication in PR

Footprints of the QCD Crossover on Cosmological Gravitational Waves at Pulsar Timing Arrays

Pulsar Timing Arrays (PTAs) have reported evidence for a stochastic gravitational wave (GW) background at nHz frequencies, possibly originating in the early Universe. We show that the spectral shape of the low-frequency (causality) tail of GW signals sourced at temperatures around $T\gtrsim 1$ GeV is distinctively affected by confinement of strong interactions (QCD), due to the corresponding sharp decrease in the number of relativistic species. A Bayesian analysis in the latest International PTA dataset reveals a significant improvement in the fit with respect to cubic power law spectra, previously employed for the causality tail. Comparison with the results of NANOGrav 15 years and European PTA Data Release 2 suggests that our inclusion of Standard Model effects on GWs can have a potentially decisive impact on model selection.Comment: 6+9 pages, 7 figure