arXiv subjects

K. Moffat

Publications and source records attributed to K. Moffat.

6 recordsLinked to original sources

arXiv2021

Flavoured Resonant Leptogenesis at Sub-TeV Scales

We consider sub-TeV scale flavoured resonant leptogenesis within the minimal type-I seesaw scenario with two right-handed singlet neutrinos $N_{1,2}$ forming a pseudo-Dirac pair, concentrating on the case of masses of the pseudo-Dirac pair having values $M_{1,2} \lesssim 100$ GeV. The case when the CP violating asymmetries in the individual lepton charges $L_l$, $l=e,μ,τ$, and in the total lepton charge $L$ of the Universe are generated in $1 \leftrightarrow 2$ decay processes is investigated. We show that successful leptogenesis is possible for $M_{1,2}$ lying in the interval $M_{1,2} = (0.3 - 100)$ GeV. Our results show also, in particular, that for vanishing initial $N_{1,2}$ abundance, flavour effects can play an important role in the generation of the baryon asymmetry, leading to an enhancement of the asymmetry by a factor up to $\sim 300$ with respect to the "unflavoured" leptogenesis scenario.

hep-ph↗

arXiv2021

Aspects of High Scale Leptogenesis with Low-Energy Leptonic CP Violation

Using the density matrix equations (DME) for high scale leptogenesis based on the type I seesaw mechanism, in which the CP violation (CPV) is provided by the low-energy Dirac or/and Majorana phases of the neutrino mixing (PMNS) matrix, we investigate the 1-to-2 and the 2-to-3 flavour regime transitions, where the 1, 2 and 3 leptogenesis flavour regimes in the generation of the baryon asymmetry of the Universe $η_B$ are described by the Boltzmann equations. Concentrating on the 1-to-2 flavour transition we determine the general conditions under which $η_B$ goes through zero and changes sign in the transition. Analysing in detail the behaviour of $η_B$ in the transition in the case of two heavy Majorana neutrinos $N_{1,2}$ with hierarchical masses, $M_1 \ll M_2$, we find, in particular, that i) the Boltzmann equations in many cases fail to describe correctly the generation of $η_B$ in the 1, 2 and 3 flavour regimes, ii) the 2-flavour regime can persist above (below) $\sim 10^{12}$ GeV ($\sim 10^9$ GeV), iii) the flavour effects in leptogenesis persist beyond the typically considered maximal for these effects leptogenesis scale of $10^{12}$ GeV. We further determine the minimal scale $M_{1\text{min}}$ at which we can have successful leptogenesis when the CPV is provided only by the Dirac or Majorana phases of the PMNS matrix as well as the ranges of scales and values of the phases for having successful leptogenesis. We show, in particular, that when the CPV is due to the Dirac phase $δ$, there is a direct relation between the sign of $\sin δ$ and the sign of $η_B$ in the regions of viable leptogenesis in the case of normal hierarchical light neutrino mass spectrum; for the inverted hierarchical spectrum the same result holds for $M_1 \lesssim 10^{13}$ GeV. The considered scenarios of leptogenesis are testable and falsifiable in low-energy neutrino experiments.

hep-ph↗

arXiv2019

Leptogenesis in the Neutrino Option

We examine the compatibility between the Neutrino Option, in which the electroweak scale is generated by PeV mass type I seesaw Majorana neutrinos, and leptogenesis. We find the Neutrino Option is consistent with resonant leptogenesis. Working within the minimal seesaw scenario with two heavy Majorana neutrinos $N_{1,2}$, which form a pseudo-Dirac pair, we explore the viable parameter space. We find that the Neutrino Option and successful leptogenesis are compatible in the cases of a neutrino mass spectrum with normal (inverted) ordering for $1.2 \times 10^6 < M \text{ (GeV)} < 8.8 \times 10^6$ ($2.4 \times 10^6 < M \text{ (GeV)} < 7.4 \times 10^6$), with $M = (M_1 + M_2)/2$ and $M_{1,2}$ the masses of $N_{1,2}$. Successful leptogenesis requires that $ΔM/M \equiv (M_2 - M_1)/M \sim 10^{-8}$. We further show that leptogenesis can produce the baryon asymmetry of the Universe within the Neutrino Option scenario when the requisite CP violation in leptogenesis is provided exclusively by the Dirac or Majorana low energy CP violation phases of the PMNS matrix.

hep-ph↗

arXiv2019

Leptogenesis from Low Energy $CP$ Violation

We revisit the possibility of producing the observed baryon asymmetry of the Universe via thermal leptogenesis, where $CP$ violation comes exclusively from the low-energy phases of the neutrino mixing matrix. We demonstrate the viability of thermal flavoured leptogenesis across seven orders of magnitude $\left(10^{6}<T \text{ (GeV)}< 10^{13}\right)$, using modern numerical machinery, where the lower bound can be reached only if flavour effects are taken into account and its value depends on the allowed degree of cancellation between the tree-level and radiative contributions to the light neutrino masses. At very high scales $\left( T \gg 10^{12} \text{ GeV} \right)$, we clarify that thermal leptogenesis is sensitive to the low-energy phases, in contradiction with what is usually claimed in the literature. In particular we demonstrate that Majorana-phase leptogenesis is in general viable while Dirac-phase leptogenesis requires some level of fine-tuning.

hep-ph↗

arXiv2018

Three-Flavoured Non-Resonant Leptogenesis at Intermediate Scales

Leptogenesis can successfully explain the matter-antimatter asymmetry via out-of-equilibrium decays of heavy Majorana neutrinos in the early Universe. In this article, we focus on non-resonant thermal leptogenesis and the possibility of lowering its scale. In order to do so, we calculate the lepton asymmetry produced from the decays of one and two heavy Majorana neutrinos using three-flavoured density matrix equations in an exhaustive exploration of the model parameter space. We find regions of the parameter space where thermal leptogenesis is viable at intermediate scales, $T\sim 10^{6}$ GeV. However, the viability of thermal leptogenesis at such scales requires a certain degree of cancellation between the tree and one-loop level contribution to the light neutrino mass matrix and we quantify such fine-tuning.

hep-ph↗

arXiv2017

Equivalence between massless neutrinos and lepton number conservation in fermionic singlet extensions of the Standard Model

We discuss the most general necessary and sufficient condition for three massless light neutrinos in variants of the type I seesaw mechanism in which we introduce an arbitrary number of fermionic gauge singlets. We find that having massless light neutrinos is equivalent to enforcing the conservation of lepton number. As a consequence, any symmetry that leads to massless light neutrinos will contain as an unbroken subgroup a conserved lepton number. This will be important for searches for heavy sterile neutrinos since in general the light neutrino masses will be proportional to small lepton number violating parameters that will also suppress lepton number violating signatures.

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