γ\gamma-ray and ultra-high energy neutrino background suppression due to solar radiation

The Sun emits copious amounts of photons and neutrinos in an approximately spatially isotropic distribution. Diffuse $\gamma$-rays and ultra-high energy (UHE) neutrinos from extragalactic sources may subsequently interact and annihilate with the emitted solar photons and neutrinos respectively. This will in turn induce an anisotropy in the cosmic ray background due to attenuation of the $\gamma$-ray and UHE neutrino flux by the solar radiation. Measuring this reduction, therefore, presents a simple and powerful astrophysical probe of electroweak interactions. In this letter we compute such anisotropies, which at the Earth (Sun) can be $\simeq 2\times 10^{-3}\,(0.5)\%$ and $\simeq 1\times 10^{-16}\,(2\times 10^{-14})\%$ for TeV scale $\gamma$-rays and PeV scale UHE neutrinos respectively. We briefly discuss exciting observational prospects for experiments such as the Fermi Gamma-Ray Space Telescope Large Area Telescope (Fermi LAT), High Energy Stereoscopic System (H.E.S.S), High-Altitude Water Cherenkov (HAWC) detector and IceCube. The potential for measuring $\gamma$-ray attenuation at orbital locations of other active satellites such as the Parker Solar Probe and James Webb Space Telescope is also explored.Comment: 6 pages, 3 figure

Exploring Extended Scalar Sectors, Neutrinos and Flavour Anomalies

The best current theory describing the fundamental interactions of matter in our universe is the Standard Model of Particle Physics. However, it leaves many important physical questions unanswered. These include, providing an explanation for the predominance of matter over antimatter, the origin of neutrino masses, unification of quantum gauge fields at high energy scales as well as flavour violation as hinted at by results of recent experiments. This thesis focuses on providing explanations for these questions whilst outlining solutions that predict phenomena that can be tested in collider searches and cosmological observables. We begin with a presentation of a dedicated search for new Higgs particles at the Large Hadron Collider. The physics analysis, performed with data drawn from the ATLAS experiment, focuses on Two-Higgs-Doublet models, which provide an elegant explanation for the abundance of matter over antimatter in our universe through an early universe cosmological phase transition. We then explicitly calculate such a phase transition dynamically and the speed with which it propagates in the early universe plasma for a particular extended scalar potential. Such transitions produce compelling phenomenology such as gravitational waves that could be detected at interferometer experiments such as LIGO. Beyond this, we explore the phenomena of CP violation which is a necessary condition for generation of matter-antimatter asymmetry. Here, we calculate novel CP properties of fermions such as the CP asymmetry in the neutrino and top quark transition dipole moments. Such properties directly affect their respective decay rates for several interesting channels. Finally, we explore grand unified field theories that yield exotic low energy phenomenology and thereby provide UV complete explanations for tensions in the flavour sector. These tensions provide some of the most compelling experimental evidence yet for physics beyond the Standard Model

Cosmological parameters from Planck data in SU(2)CMB_{\rm CMB}, their local Λ\LambdaCDM values, and the modified photon Boltzmann equation

A review of the spatially flat cosmological model SU(2)$_{\rm CMB}$, minimally induced by the postulate that the Cosmic Microwave Background (CMB) is subject to an SU(2) rather than a U(1) gauge principle, is given. Cosmological parameter values, which are determined from the Planck CMB power spectra at small angular scales, are compared to their values in spatially flat $\Lambda$CDM from both local and global extractions. As a global model SU(2)$_{\rm CMB}$ leans towards local $\Lambda$CDM cosmology and is in tension with some global $\Lambda$CDM parameter values. We present spectral antiscreening / screening effects in SU(2)$_{\rm CMB}$ radiance within the Rayleigh-Jeans regime in dependence on temperature and frequency. Such radiance anomalies can cause CMB large-angle anomalies. Therefore, it is pointed out how SU(2)$_{\rm CMB}$ modifies the Boltzmann equation for the perturbations of the photon phase space distribution at low redshift and why this requires to the solve the $\ell$-hierarchy on a comoving momentum grid ($q$-grid) for all $z$.Comment: 9 pages, 7 figure

Dark Matter spikes around Sgr A* in γ\gamma-rays

We use H.E.S.S. $\gamma$-ray observations of Sgr A* to derive novel limits on the Dark Matter (DM) annihilation cross-section. We quantify their dependence on uncertainties i) in the DM halo profile, which we vary from peaked to cored, and ii) in the shape of the DM spike around Sgr A*, dynamically heated by the nuclear star cluster. For peaked halo profiles and depending on the heating of the spike, our limits are the strongest existing ones for DM masses above a few TeV. Our study contributes to assessing the influence of the advancements in our knowledge of the Milky Way on determining the properties of DM particles.Comment: Published in JCAP, added discussion on energy resolution impact for DM annihilation into photons channe

CP violation in neutral lepton transition dipole moment

The CP violation in the neutrino transition electromagnetic dipole moment is discussed in the context of the Standard Model with an arbitrary number of right-handed singlet neutrinos. A full one-loop calculation of the neutrino electromagnetic form factors is performed in the Feynman gauge. A non-zero CP asymmetry is generated by a required threshold condition for the neutrino masses along with non-vanishing CP violating phases in the lepton flavour mixing matrix. We follow the paradiagm of CP violation in neutrino oscillations to parametrise the flavour mixing contribution into a series of Jarlskog-like parameters. This formalism is then applied to a minimal seesaw model with two heavy right-handed neutrinos denoted N1 and N2. We observe that the CP asymmetries for decays into light neutrinos N → νγ are extremely suppressed, maximally around 10−17. However the CP asymmetry for N2 → N1γ can reach of order unity. Even if the Dirac CP phase δ is the only source of CP violation, a large CP asymmetry around 10−5–10−3 is comfortably achieved

Planck Constraints and Gravitational Wave Forecasts for Primordial Black Hole Dark Matter Seeded by Multifield Inflation

We perform a Markov Chain Monte Carlo (MCMC) analysis of a simple yet generic multifield inflation model characterized by two scalar fields coupled to each other and nonminimally coupled to gravity, fit to Planck 2018 cosmic microwave background (CMB) data. In particular, model parameters are constrained by data on the amplitude of the primordial power spectrum of scalar curvature perturbations on CMB scales $A_s$, the spectral index $n_s$, and the ratio of power in tensor to scalar modes $r$, with a prior that the primordial power spectrum should also lead to primordial black hole (PBH) production sufficient to account for the observed dark matter (DM) abundance. We find that $n_s$ in particular controls the constraints on our model. Whereas previous studies of PBH formation from an ultra-slow-roll phase of inflation have highlighted the need for at least one model parameter to be highly fine-tuned, we identify a degeneracy direction in parameter space such that shifts by $\sim 10\%$ of one parameter can be compensated by comparable shifts in other parameters while preserving a close fit between model predictions and observations. Furthermore, we find this allowed parameter region produces observable gravitational wave (GW) signals in the frequency ranges to which upcoming experiments are projected to be sensitive, including Advanced LIGO and Virgo, the Einstein Telescope (ET), Cosmic Explorer (CE), DECIGO, and LISA.Comment: 27 pages, 10 figures, 2 tables. Minor edits and references added to match published version (forthcoming in Physical Review D), including an additional appendix to discuss effects on the power spectrum from a phase of ultra-slow-roll evolutio