Inflationary Baryogenesis in a Model with Gauged Baryon Number

We argue that inflationary dynamics may support a scenario where significant matter-antimatter asymmetry is generated from initially small-scale quantum fluctuations that are subsequently stretched out over large scales. This scenario can be realised in extensions of the Standard Model with an extra gauge symmetry having mixed anomalies with the electroweak gauge symmetry. Inflationary baryogenesis in a model with gauged baryon number is considered in detail.Comment: 11 pages, V3 - major revisio

Natural Inflation with Hidden Scale Invariance

We propose a new class of natural inflation models based on a hidden scale invariance. In a very generic Wilsonian effective field theory with an arbitrary number of scalar fields, which exhibits scale invariance via the dilaton, the potential necessarily contains a flat direction in the classical limit. This flat direction is lifted by small quantum corrections and inflation is realised without need for an unnatural fine-tuning. In the conformal limit, the effective potential becomes linear in the inflaton field, yielding to specific predictions for the spectral index and the tensor-to-scalar ratio, being respectively: $n_s-1\approx -0.025\left(\frac{N_{\star}}{60}\right)^{-1}$ and $r\approx 0.0667\left(\frac{N_{\star}}{60}\right)^{-1}$, where $N_{\star}\approx 30-65$ is a number of efolds during observable inflation. This predictions are in reasonable agreement with cosmological measurements. Further improvement of the accuracy of these measurements may turn out to be critical in falsifying our scenario.Comment: 8 pages, minor revision, to be published in PL

750 GeV Composite Axion as the LHC Diphoton Resonance

We propose that the 750 GeV resonance, presumably observed in the early LHC Run 2 data, could be a heavy composite axion that results from condensation of a hypothetical quark in a high-colour representation of conventional QCD. The model, motivated by a recently proposed solution to the strong CP problem, is very economical and is essentially defined by the properties of the additional quark - its colour charge, hypercharge and mass. The axion mass and its coupling to two photons (via axial anomaly) can be computed in terms of these parameters. The axion is predominantly produced via photon fusion ($\gamma\gamma \to {\cal A}$) which is followed by $Z$ vector boson fusion and associated production at the LHC. We find that the total diphoton cross section of the axion can be fitted with the observed excess. Combining the requirement on the cross-section, such that it reproduces the diphoton excess events, with the bounds on the total width ($\Gamma_{tot} \leqslant 45$ GeV), we obtain the effective coupling in the range $1.6\times 10^{-4}$ GeV$^{-1}\gtrsim C_{{\cal A}} \gtrsim 6.5\times 10^{-5}$ GeV$^{-1}$. Within this window of allowed couplings the model favours a narrow width resonance and $y_{Q}^2 \sim \mathcal{O}(10)$. In addition, we observe that the associated production $q\bar{q} \to {\cal A}\gamma\to \gamma\gamma\gamma$ can potentially produce a sizeable number of three photon events at future LHC and $e^{+} e^{-}$ colliders. However, the rare decay $Z\to\mathcal{A}^*\gamma \to \gamma\gamma\gamma$ is found to be too small to be probed at the LHC.Comment: 10 pages, 3 figures; Minor revision, updated references to be consistent with PLB published versio

Gravitational Leptogenesis in Bounce Cosmology

We investigate whether successful Gravitational Leptogenesis can take place during an Ekpyrotic contraction phase. Two possible paths by which this can occur are coupling the Ekpyrotic scalar to a gravitational Chern-Simons term, or to a $U(1)$ gauge field Chern-Simons term. These couplings lead to the production of chiral gravitational waves, which generate a lepton number asymmetry through the gravitational-lepton number anomaly. This lepton asymmetry is subsequently reprocessed by equilibrium sphaleron processes to produce a baryon asymmetry. We find successful Gravitational Leptogenesis to be possible in Ekpyrotic bounce cosmologies through both of these mechanisms.Comment: 31 pages, 17 figure

The Evolution, Current Status, and Future Prospects of Using Biotechnologies in the Mineral Extraction and Metal Recovery Sectors

The current global demand in terms of both the amounts and range of metals for industrial and domestic use greatly exceeds that at any previous time in human history. Recycling is inadequate to meet these needs and therefore mining primary metal ores will continue to be a major industry in the foreseeable future. The question of how metal mining can develop in a manner which is less demanding of energy and less damaging of the environment in a world whose population is increasingly aware of, and concerned about, the environment, requires urgent redress. Increased application of biotechnologies in the mining sector could go some way in solving this conundrum, yet, biomining (harnessing microorganisms to enhance the recovery of base and precious metals) has remained a niche application since it was first knowingly used in the 1960s. This manuscript reviews the development and current status of biomining applications and highlights their limitations as well as their strengths. New areas of biotechnology that could be applied in the mining sector, and their potential impact in terms of both their potential environmental and economic benefits, are also discussed

Resonant Vector Dark Matter Production during Inflation

We present a new mechanism for generating the observed dark matter energy density, through resonant production of vector dark matter during inflation. Resonant amplification of the vector dark matter is achieved through Mathieu instabilities induced by an oscillatory coupling with the inflaton, which can occur as early as 11.9 e-folds before the end of inflation. Successful dark matter production is possible for a wide range of inflationary Hubble rates and vector mass scales. This scenario generates both helicity states of the vector dark matter density in contrast to other tachyonic production mechanisms, while exhibiting large parameter regions with negligible energy density generated in the longitudinal mode. The discovery of this dark matter candidate will not only explain the nature of dark matter but provide insight into the inflationary potential and the scale of inflation. The allowed parameter space is surveyed and the unique phenomenological implications are discussed, which include gravitational waves and the dark matter energy density spectrum.Comment: 18 pages, 2 figure

Pendulum Leptogenesis

We propose a new non-thermal Leptogenesis mechanism that takes place during the reheating epoch, and utilizes the Ratchet mechanism. The interplay between the oscillation of the inflaton during reheating and a scalar lepton leads to a dynamical system that emulates the well-known forced pendulum. This is found to produce driven motion in the phase of the scalar lepton which leads to the generation of a non-zero lepton number density that is later redistributed to baryon number via sphaleron processes. This model successfully reproduces the observed baryon asymmetry, while simultaneously providing an origin for neutrino masses via the seesaw mechanism.Comment: 14 pages, no figures; minor revision to match PL