51 research outputs found

### 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

### 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

### 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

### 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

### Affleck-Dine Dirac Leptogenesis

We present a minimal framework that realises successful Dirac Leptogenesis
through the Affleck-Dine mechanism. A single right-handed neutrino and a
neutrinophillic Higgs doublet are introduced to the Standard Model, which
couple via a Yukawa interaction. The inflationary setting is induced by a
combination of the two Higgs doublets, with their global symmetry violating
interactions leading to a net charge generation via the Affleck-Dine mechanism.
This simple Standard Model extension exhibits a unique and connected set of
phenomenological implications including the resultant baryon asymmetry,
inflationary predictions, cosmological implications, relic right-handed
neutrinos, and its low energy phenomenology, while also being able to be
embedded in various neutrino mass generating mechanisms.Comment: 6 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

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