Number Violation Research Articles

Baryogenesis via leptogenesis: Spontaneous B and L violation

In order to address the baryon asymmetry in the Universe one needs to understand the origin of baryon (B) and lepton (L) number violation. In this article, we discuss the mechanism of baryogenesis via leptogenesis to explain the matter-antimatter asymmetry in theories with spontaneous breaking of baryon and lepton number. In this context, a lepton asymmetry is generated through the out-of-equilibrium decays of right-handed neutrinos at the high-scale, while local baryon number must be broken below the multi-TeV scale to satisfy the cosmological bounds on the dark matter relic density. We demonstrate how the lepton asymmetry generated via leptogenesis can be converted in two different ways: a) in the theory predicting Majorana dark matter the lepton asymmetry is converted into a baryon asymmetry, and b) in the theory with Dirac dark matter the decays of right-handed neutrinos can generate lepton and dark matter asymmetries that are then partially converted into a baryon asymmetry. Consequently, we show how to explain the matter-antimatter asymmetry, the dark matter relic density and neutrino masses in theories for local baryon and lepton number.

The NA62 experiment at CERN

is one of the theoretically cleanest meson decay where to look for indirect effects of new physics complementary to LHC searches. The NA62 experiment at CERN SPS is designed to measure the branching ratio of this decay with 10% precision. NA62 took data in 2014 and 2015 and will accumulate kaon decays till the end of 2018. The quality of data acquired in view of the final measurement will be presented. The experiment is also collecting data to search for exotic processes, like Lepton Flavour and Number violation and Axions.

Baryon asymmetry from primordial black holes

We propose a new scenario of the baryogenesis from primordial black holes (PBH). Assuming presence of microscopic baryon (or lepton) number violation and a CP violating operator such as $\partial_\alpha F(\mathcal{R_{....}} ) J^\alpha$, where $F(\mathcal{R_{....}})$ is a scalar function of the Riemann tensor, time evolution of an evaporating black hole generates baryonic (leptonic) chemical potential at the horizon; consequently PBH enumerates asymmetric Hawking radiation between baryons (leptons) and anti-baryons (leptons). Though the operator is higher dimensional and largely suppressed by a high mass scale $M_*$, we show that sufficient amount of asymmetry can be generated for a wide range of parameters of the PBH mass $M_{\rm PBH}$, its abundance $\Omega_{\rm PBH}$, and the scale $M_*$.

μ − – e + conversion in upcoming LFV experiments

We present an illustrative discussion of the physics potential of $\mu^-$- $e^+$ conversion. We point out that this process, although much less frequently studied than the related but much more popular processes of $\mu^-$- $e^-$ conversion and neutrinoless double beta decay, in fact is a promising alternative possibility to detect both lepton flavour and number violation. However, for this goal to be reached, a combined effort of experiments and theory, both in nuclear and particle physics, is necessary to advance. The aim of this paper is to be an "appetiser" to trigger such an initiative.

Phi-features reloaded: An event-related potential study on person and number agreement processing

ABSTRACTLinguistic analysis claims that verb agreement is composed of distinct phi-features such as person and number, but are these different phi-features processed distinctly or similarly? We used a sentence grammaticality task to explore the electrophysiological responses of Basque speakers when processing subject–verb person and number phi-feature agreement violations. We generated grammatical structures (grammatical control) and ungrammatical structures in which the verb disagreed with the subject in person (person violation), in number (number violation), or in both person and number features (person+number violation). Behavioral data revealed that, overall, participants were faster and more accurate detecting person and person+number violations than violations involving only number. Event-related potential responses revealed a N400–P600 pattern for all violation types. Person and person+number violations elicited larger P600 effects than number violations. These findings reveal different costs related to the processing of person and number phi-feature agreement and indicate that these features are distinct components of agreement computation.

Flavour covariant transport equations: An application to resonant leptogenesis

We present a fully flavour-covariant formalism for transport phenomena, by deriving Markovian master equations that describe the time-evolution of particle number densities in a statistical ensemble with arbitrary flavour content. As an application of this general formalism, we study flavour effects in a scenario of resonant leptogenesis (RL) and obtain the flavour-covariant evolution equations for heavy-neutrino and lepton number densities. This provides a complete and unified description of RL, capturing three distinct physical phenomena: (i) the resonant mixing between the heavy-neutrino states, (ii) coherent oscillations between different heavy-neutrino flavours, and (iii) quantum decoherence effects in the charged-lepton sector. To illustrate the importance of this formalism, we numerically solve the flavour-covariant rate equations for a minimal RL model and show that the total lepton asymmetry can be enhanced by up to one order of magnitude, as compared to that obtained from flavour-diagonal or partially flavour off-diagonal rate equations. Thus, the viable RL model parameter space is enlarged, thereby enhancing further the prospects of probing a common origin of neutrino masses and the baryon asymmetry in the Universe at the LHC, as well as in low-energy experiments searching for lepton flavour and number violation. The key new ingredients in our flavour-covariant formalism are rank-4 rate tensors, which are required for the consistency of our flavour-mixing treatment, as shown by an explicit calculation of the relevant transition amplitudes by generalizing the optical theorem. We also provide a geometric and physical interpretation of the heavy-neutrino degeneracy limits in the minimal RL scenario. Finally, we comment on the consistency of various suggested forms for the heavy-neutrino self-energy regulator in the lepton-number conserving limit.

τ→μηin supersymmetric models

The existence of large ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{-}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ mixing suggests the likelihood of large smuon-stau mixing in supersymmetric models, leading to \ensuremath{\mu} and \ensuremath{\tau} number violation. In addition to interesting signatures in slepton and neutralino production and decay, this will lead to rare \ensuremath{\tau} decays, such as $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}\ensuremath{\gamma}.$ Recently, it has been pointed out that the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}3\ensuremath{\mu}$ branching ratio could be substantial in the large $\mathrm{tan}\ensuremath{\beta}$ region of parameter space, due to an induced $\ensuremath{\mu}\ensuremath{-}\ensuremath{\tau}$-Higgs vertex. In this paper, another signature, $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}\ensuremath{\eta}$ is considered. In the large $\mathrm{tan}\ensuremath{\beta}$ region, it is shown that the branching ratio of $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}\ensuremath{\eta}$ is 8.4 times the branching ratio of $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}3\ensuremath{\mu},$ independent of any unknown parameters, and it will thus give the most stringent bound on Higgs-mediated lepton flavor violation, and may provide its first signature. In the other regions of parameter space, where $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}\ensuremath{\gamma}$ is the most prominent decay, the branching ratio for $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}\ensuremath{\eta}$ is always substantially lower.

Trio coherent states

Novel states called trio coherent states are introduced and studied. It is shown that these states possess inherent nonclassical properties such as sub-Poissonian number distributions and violation of Cauchy-Schwarz inequalities. Concerning squeezing, though the usual multimode squeezing is absent, a new type of higher-order multimode squeezing may occur in a trio coherent state. Finally, an experimental scheme is proposed to generate the introduced trio coherent state.

Explicit R-parity breaking in supersymmetric models

Supersymmetric models generally invoke R parity to ensure that baryon and lepton numbers are symmetries of the renormalizable operators of the low-energy effective theory. The phenomenology of lepton-number violation is analyzed in low-energy models in which R parity is explicitly broken by superrenormalizable operators. Constraints on lepton-number violating parameters are found to be mild. The photino is able to decay, avoiding a stringent cosmological lower bound on its mass. Alternatives to R parity are considered in the context of an SU(5) grand unified model coupled to N=1 supergravity. One possibility, θ parity, leads to new mechanisms for baryon- number violation in addition to lepton-number violation.