arXiv subjects

Neil D. Barrie

Publications and source records attributed to Neil D. Barrie.

At least 19 recordsLinked to original sources

arXiv2024

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.

hep-ph↗

arXiv2022

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.

hep-ph↗

arXiv2022

Type II Seesaw Leptogenesis

The Type II Seesaw Mechanism provides a minimal framework to explain the neutrino masses involving the introduction of a single triplet Higgs to the Standard Model. However, this simple extension was believed to be unable to successfully explain the observed baryon asymmetry of the universe through Leptogenesis. In our previous work (Phys. Rev. Lett. 128, 141801), we demonstrated that the triplet Higgs of the Type II Seesaw Mechanism alone can simultaneously generate the observed baryon asymmetry of the universe and the neutrino masses while playing a role in setting up Inflation. This is achievable with a triplet Higgs mass as low as 1 TeV, and predicts that the neutral component obtains a small vacuum expectation value $v_Δ< 10 $ keV. We find that our model has very rich phenomenology and can be tested by various terrestrial experiments as well as by astronomical observations. Particularly, we show that the successful parameter region may be probed at a future 100 TeV collider, upcoming lepton flavor violation experiments such as Mu3e, and neutrinoless double beta decay experiments. Additionally, the tensor-to-scalar ratio from the inflationary scenario will be probed by the LiteBIRD telescope, and observable isocurvature perturbations may be produced for some parameter choices. In this article, we present all the technical details of our calculations and further discussion of its phenomenological implications.

hep-ph↗

arXiv2022

Affleck-Dine Leptogenesis from Higgs Inflation

We find that the triplet Higgs of the Type II seesaw mechanism can simultaneously generate the neutrino masses and observed baryon asymmetry, while playing a role in inflation. We survey the allowed parameter space and determine that this is possible for triplet masses as low as a TeV, with a preference for a small vacuum expectation value for the triplet $v_Δ< 10 $ keV. This requires that the triplet Higgs must decay dominantly into the leptonic channel. Additionally, this model will be probed at the future 100 TeV collider, upcoming lepton flavor violation experiments such as Mu3e, and neutrinoless double beta decay experiments. Thus, this simple framework provides a unified solution to the three major unknowns of modern physics - inflation, the neutrino masses, and the observed baryon asymmetry - while simultaneously providing unique phenomenological predictions that will be probed terrestrially at upcoming experiments.

hep-ph↗

arXiv2021

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.

hep-ph↗

arXiv2021

Searching for Monopoles via Monopolium Multiphoton Decays

We explore the phenomenology of a model of monopolium based on an electromagnetic dual formulation of Zwanziger and lattice gauge theory. The monopole is assumed to have a finite-sized inner structure based on a 't Hooft-Polyakov like solution, with the magnetic charge uniformly distributed on the surface of a sphere. The monopole and anti-monopole potential becomes linear plus Coulomb outside the sphere, analogous to the Cornell potential utilised in the study of quarkonium states. Discovery of a resonance feature in the diphoton channel as well as in a higher multiplicity photon channel would be a smoking gun for the existence of monopoles within this monopolium construction, with the mass and bound state properties extractable. Utilising the current LHC results in the diphoton channel, constraints on the monopole mass are determined for a wide range of model parameters. These are compared to the most recent MoEDAL results and found to be significantly more stringent in certain parameter regions, providing strong motivation for exploring higher multiplicity photon final state searches.

hep-ph↗

arXiv2020

Higgs Inflation, Vacuum Stability, and Leptogenesis

We consider the introduction of a complex scalar field carrying a global lepton number charge to the Standard Model and the Higgs inflation framework. The conditions are investigated under which this model can simultaneously ensure Higgs vacuum stability up to the Planck scale, successful inflation, non-thermal Leptogenesis via the pendulum mechanism, and light neutrino masses. These can be simultaneously achieved when the scalar lepton is minimally coupled to gravity, that is, when standard Higgs inflation and reheating proceed without the interference of the additional scalar degrees of freedom. If the scalar lepton also has a non-minimal coupling to gravity, a multi-field inflation scenario is induced, with interesting interplay between the successful inflation constraints and those from vacuum stability and Leptogenesis. The parameter region that can simultaneously achieve the above goals is explored.

hep-ph↗

arXiv2020

Big Bounce Baryogenesis

We explore the possibility of an Ekpyrotic contraction phase harbouring a mechanism for Baryogenesis. A Chern-Simons coupling between the fast-rolling Ekpyrotic scalar and the Standard Model Hypercharge gauge field enables the generation of a non-zero helicity during the contraction phase. The baryon number subsequently produced at the Electroweak Phase Transition is consistent with observation for a range of couplings and bounce scales. Simultaneously, the gauge field production during the contraction provides the seeds for galactic magnetic fields and sources gravitational waves, which may provide additional avenues for observational confirmation.

hep-ph↗

arXiv2020

Gravitational Instabilities of the Cosmic Neutrino Background with Non-zero Lepton Number

We argue that a cosmic neutrino background that carries non-zero lepton charge develops gravitational instabilities. Fundamentally, these instabilities are related to the mixed gravity-lepton number anomaly. We have explicitly computed the gravitational Chern-Simons term which is generated quantum-mechanically in the effective action in the presence of a lepton number asymmetric neutrino background. The induced Chern-Simons term has a twofold effect: (i) gravitational waves propagating in such a neutrino background exhibit birefringent behaviour leading to an enhancement/suppression of the gravitational wave amplitudes depending on the polarisation, where the magnitude of this effect is related to the size of the lepton asymmetry; (ii) Negative energy graviton modes are induced in the high frequency regime, which leads to very fast vacuum decay producing, e.g., positive energy photons and negative energy gravitons. From the constraint on the present radiation energy density, we obtain an interesting bound on the lepton asymmetry of the universe.

hep-ph↗

arXiv2019

Broken Democracy with Intermediate $\mathbb S_2 \times \mathbb S_2$ Residual Symmetry and Random Perturbations

The democratic mass matrix is an intriguing possibility for explaining the observed fermion mixings due to its inherent hierarchical mass eigenvalues and large mixing angles. Nevertheless, two of the three mass eigenvalues are zero if the flavor democracy is exact, in obvious contradiction with the experimental observations. One possibility is breaking the flavor democracy with anarchical perturbations as we proposed in an earlier work. However, even within the first two generations, the charged fermion masses are also hierarchical which may not be a coincidence. The democratic $\mathbb S^L_3 \times \mathbb S^R_3$ symmetry of the three generations may first be broken down to an intermediate $\mathbb S^L_2 \times \mathbb S^R_2$ symmetry among the first two generations to regulate the sequential hierarchies, followed by random perturbations, that generate the correct size of all measured observables. Unique predictions for neutrinoless double beta decay are also found.

hep-ph↗

arXiv2018

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.

hep-ph↗

arXiv2018

Ratchet Baryogenesis with an Analogy to the Forced Pendulum

A new scenario of baryogenesis via the ratchet mechanism is proposed based on an analogy to the forced pendulum. The oscillation of the inflaton field during the reheating epoch after inflation plays the role of the driving force, while the phase $θ$ of a scalar baryon field (a complex scalar field with baryon number) plays the role of the angle of the pendulum. When the inflaton is coupled to the scalar baryon, the behavior of the phase $θ$ can be analogous to that of the angle of the forced pendulum. If the oscillation of the driving force is adjusted to the pendulum's motion, a directed rotation of the pendulum is obtained with a non-vanishing value of $\dotθ$, which models successful baryogenesis since $\dotθ$ is proportional to the baryon number density. Similar ratchet models which lead to directed motion have been used in the study of molecular motors in biology. There, the driving force is supplied by chemical reactions, while in our scenario this role is played by the inflaton during the reheating epoch. Keywords: Baryogenesis; Reheating; Inflaton; Ratchet Model; Forced Rotating Pendulum

hep-ph↗

arXiv2018

Exotic Lepton Searches via Bound State Production at the LHC

Heavy long-lived multi-charged leptons (MCLs) are predicted by various new physics models. These hypothetical MCLs can form bound states, due to their high electric charges and long life times. In this work, we propose a novel strategy of searching for MCLs through their bound state productions and decays. By utilizing LHC-8 TeV data in searching for resonances in the diphoton channel, we exclude the masses of isospin singlet heavy leptons with electric charge $|q|\geq 6$ (in units of electron charge) lower than $\sim$1.2 TeV, which are much stronger than the corresponding 8 TeV LHC bounds from analysing the high ionisation and the long time-of-flight of MCLs. By utilising the current 13 TeV LHC diphoton channel measurements the bound can further exclude MCL masses up to $\sim$1.6 TeV for $|q|\geq 6$. Also, we demonstrate that the conventional LHC limits from searching for MCLs produced via Drell-Yan processes can be enhanced by including the contribution of photon fusion processes.

hep-ph↗

arXiv2016

Construction of a Model of Monopolium and its Search via Multi-Photon Channels at LHC

A model of monopolium is constructed based on an electromagnetic dual formulation of Zwanziger and lattice gauge theory. To cope with the strong coupling nature of the magnetic charge, for which the monopole is confined, $ U(1) $ lattice gauge theory is applied. The monopole is assumed to have a finite-sized inner structure based on a 't Hooft-Polyakov like solution in which the magnetic charge is uniformly distributed on the surface of a sphere. The monopole and antimonopole potential becomes linear plus Coulomb outside the sphere and is constant inside. Numerical estimation gives two kinds of solutions: One which has a small binding energy, and hence the para-($ J=0 $) and ortho-($ J=1 $) monopoliums have degenerate masses. For the parameter choices considered, they both have $ \mathcal{O}(1-10) $ TeV masses and are very short-lived. The other solution has a small monopole mass and large binding energy, with an illustrative example of parameter choices giving a 750 GeV para-monopolium and 1.4 TeV ortho-monopolium. The production rate of the former is one order of magnitude smaller than the announced enhancement, but they may be the target of future LHC searches and the 100 TeV colliders.

hep-ph↗

arXiv2016

Heavy Leptonium as the Origin of the 750 GeV Diphoton Excess

We propose a hypothetical heavy leptonium, the scalar bound state of an exotic lepton-antilepton pair, as a candidate for the recent 750 GeV resonance in the early LHC Run 2 data. Such a para-leptonium is dominantly produced via photon-photon fusion at the LHC and decays into a photon pair with a significant branching fraction. In addition, our model predicts a companion spin-1 ortho-leptonium bound state, which can decay to $W^+W^-$, $f\bar{f}$ and three photons. Under the LHC and the electroweak precision observables bounds, we find that the observed excess of 750 GeV diphoton events can be explained within $2σ$ accuracy for $Y_{L} \approx 4.8 - 7.2$ for the minimal case in our scenario. The observation of the ortho-leptonium in the dilepton channel will be the smoking gun for our scenario.

hep-ph↗

arXiv2016

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 ($γγ\to {\cal A}$) 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 ($Γ_{tot} \leqslant 45$ 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 $q\bar{q} \to {\cal A}γ\to γγγ$ can potentially produce a sizeable number of three photon events at future LHC and $ e^{+} e^{-} $ colliders. However, the rare decay $Z\to\mathcal{A}^*γ\to γγγ$ is found to be too small to be probed at the LHC.

hep-ph↗

arXiv2016

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.

gr-qc↗

arXiv2015

Generating Luminous and Dark Matter During Inflation

We propose a new mechanism for generating both luminous and dark matter during cosmic inflation. According to this mechanism, ordinary and dark matter carry common charge which is associated with an anomalous $ U(1)_{X} $ group. Anomaly terms source $ \mathcal{CP} $ and $ U(1)_{X} $ charge violating processes during inflation, producing corresponding non-zero Chern-Simons numbers which are subsequently reprocessed into baryon and dark matter densities. The general framework developed is then applied to two possible extensions of the Standard Model with anomalous gauged $B$ and $B-L$, each with an additional dark matter candidate.

hep-ph↗