Leptoflavorgenesis: baryon asymmetry of the Universe from lepton flavor violation

Abstract

Charged-lepton flavor violation (CLFV) is a smoking-gun signature of physics beyond the Standard Model. The discovery of CLFV in upcoming experiments would indicate that CLFV processes must have been efficient in the early Universe at relatively low temperatures. In this letter, we point out that such efficient CLFV interactions open up new ways of creating the baryon asymmetry of the Universe. First, we revisit the two-loop corrections from charged-lepton Yukawa interactions to the chemical transport in the Standard Model plasma, which imply that nonzero lepton flavor asymmetries summing up to B − L = 0 are enough to generate the baryon asymmetry. Then, we describe two scenarios of what we call leptoflavorgenesis, where efficient CLFV processes are responsible for the generation of primordial lepton flavor asymmetries that are subsequently converted to a baryon asymmetry by weak sphaleron processes. Here, the conversion factor from lepton flavor asymmetry to baryon asymmetry is suppressed by charged-lepton Yukawa couplings squared, which provides a natural explanation for the smallness of the observed baryon-to-photon ratio.Introduction. -The Standard Model (SM) of particle physics has been established observationally after the discovery of Higgs boson. Its classical action enjoys the accidental global symmetry U (1)corresponding to the conservation of the baryon charge B and the flavored lepton charges L e,µ,τ . Quantum mechanically, U (1) B +L is violated by the chiral anomaly [1].Although suppressed in the vacuum, B + L violation by means of weak sphaleron processes is efficient at temperatures 10 2 GeV T 10 12 GeV [2-5]. Also, the discovery of neutrino oscillations revealed that the lepton flavor symmetries, U (1) L e −L µ × U (1) L µ −L τ , are violated [6-10], which further implies the violation of U (1) B −L if neutrinos are Majorana fermions [11]. However, such interactions are so feeble that they could be inefficient up to T B −L ∼ 10 13 GeV, depending on possible UV completions of the neutrino sector.Charged-lepton flavor violation (CLFV) is currently attracting a lot of attention [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], since its discovery would undoubtedly imply physics beyond the SM (plus massive neutrinos), enabling us to probe new physics at extremely high energy scales, such as O 10 8 GeV by µ → eγ [13] and O 10 9 GeV by µ → ea, where a is a pseudo-Nambu-Goldstone boson like an axion or familon [22,28]. 1 This is because CLFV induced by the SM neutrino masses is extremely suppressed by the GIM mechanism [49]. Furthermore, if CLFV should be observed in upcoming experiments, we would learn that CLFV interactions must have been efficient at relatively low temperatures in the early Universe. For instance, the discovery of µ → eγ would imply that U (1) L e −L µ violating interactions are efficient at T 1 Anomalies and hints of lepton flavor universality violation in observables such as rare B meson decays [29][30][31] (see also Refs. [32,33]) and the anomalous magnetic moment ...

Early-Universe Model Building

“…More recently, a mechanism named wash-in leptogenesis [779] pointed out that the B − L asymmetry can be generated by CP violation coming from the aforementioned chiral fermions with the aid of lepton-number-violating interactions of the right-handed neutrinos, so that the annihilation of the hypermagnetic helicity and baryon asymmetry is safely avoided. The additional effects of charged-lepton flavor violation are included in wash-in leptoflavorgenesis [780].…”

“…Subsequently, the B − L asymmetry will be converted to B asymmetry via the EW sphaleron process [403]. Considering the effect of B − L and/or lepton flavor violating interactions, if they exist and are efficient after the dissipation of the AD field, may also be necessary [779,780].…”

“…Most recently, a mechanism called spontaneous leptoflavorgenesis[780] enables a non-zero baryon asymmetry to be produced from a large lepton flavor asymmetry even if the total B − L vanishes. Although the large lepton favor asymmetry may in principle result from an axion rotation, a rigorous study has not yet been carried out to show viable parameter space.…”

Cosmic Perturbations from a Rotating Field

“…MeV [79,80]. The large lepton flavor charge leads to non-zero baryon asymmetry even if B − L = 0 [81].…”

Data-driven analysis of a SUSY GUT of flavour

“…[34], it has been shown that these parameters need to be varied simultaneously in order to cover all phenomenological aspects, in particular since cancellations between different contributions may occur. Moreover, it has been demonstrated that a model may feature a reasonable amount of flavour violation while satisfying the stringent constraints of rare decays such as b → sγ or µ → eγ while sufficient lepton flavour violation may also address baryon asymmetry in the universe [38]. It is therefore interesting to pursue the study of GUT implementations of flavour violation, e.g., via flavour symmetries, in the context of low-energy and precision constraints as well as TeV-scale phenomenology.…”