We analyze the importance of flavor effects in models in which leptogenesis proceeds via the decay of Majorana electroweak triplets. We find that depending on the relative strengths of gauge and Yukawa reactions the $B-L$ asymmetry can be sizably enhanced, exceeding in some cases an order of magnitude level. We also discuss the impact that such effects can have for TeV-scale triplets showing that as long as the $B-L$ asymmetry is produced by the dynamics of the lightest such triplet they are negligible, but open the possibility for scenarios in which the asymmetry is generated above the TeV scale by heavier states, possibly surviving the TeV triplet related washouts. We investigate these cases and show how they can be disentangled at the LHC by using Majorana triplet collider observables and, in the case of minimal type III see-saw models even through lepton flavor violation observables.
We discuss scalar triplet leptogenesis in a specific left-right symmetric seesaw model. We show that the Majorana phases that are present in the model can be effectively used to saturate the existing upper limit on the CP-asymmetry of the triplets. We solve the relevant Boltzmann equations and analyze the viability of triplet leptogenesis. It is known for this kind of scenario that the efficiency of leptogenesis is maximal if there exists a hierarchy between the branching ratios of the triplet decays into leptons and Higgs particles. We show that triplet leptogenesis typically favors branching…
In the supersymmetric triplet (type-II) seesaw model, in which a single SU(2)_L-triplet couples to leptons, the high-energy neutrino flavour structure can be directly determined from the low-energy neutrino data. We show that even with such a minimal triplet content, leptogenesis can be naturally accommodated thanks to the resonant interference between superpotential and soft supersymmetry breaking terms.
We construct a supersymmetric version of the triplet Higgs model for neutrino masses, which can generate a baryon asymmetry of the Universe through lepton-number violation and is consistent with the gravitino constraints.
We present the various leptogenesis scenarios which may occur if, in addition to the ordinary heavy right-handed neutrinos, there exists a heavy scalar SU(2)_L triplet coupled to leptons. We show that the contributions of the right-handed neutrinos and the triplet to the lepton asymmetry are proportional to their respective contributions to the neutrino mass matrix. A consequence of the triplet contribution to the lepton asymmetry is that there is no more upper bound on the neutrino masses from leptogenesis due to the fact that the neutrino mass constraints do not necessarily induce asymmetry …
A simple and economical extension of the minimal standard electroweak gauge model (without right-handed neutrinos) by the addition of two heavy Higgs scalar triplets would have two significant advantages. \underline {Naturally} small Majorana neutrino masses would become possible, as well as leptogenesis in the early universe which gets converted at the electroweak phase transition into the present observed baryon asymmetry.
We reveal the origin of the CP violation required by the leptogenesis in variously popular seesaw models. Especially we clarify that in a pure type-I/III seesaw with two fermion singlets/triplets, a combined type-I+III seesaw with one fermion singlet and one fermion triplet, or a combined type-I/III+II seesaw with one fermion singlet/triplet and one Higgs triplet, the CP violation for the leptogenesis can exactly come from the imaginary part of the neutrino mass matrix in a special basis where the Yukawa couplings involving one fermion singlet/triplet are allowed to get rid of any CP phases. W…
We discuss leptogenesis in the context of type-II seesaw in the case in which in addition to the scalar electroweak triplet decays the lepton asymmetry is also induced by right-handed neutrino decays (mild hierarchical scenarios). We show that within this setup, depending on the relative sizes of the relevant parameters, one can identify three classes of generic models, each one with its own consequences for leptogenesis.
We present a flavour-covariant formalism for scalar triplet leptogenesis, which takes into account the effects of the different lepton flavours in a consistent way. Our main finding is that flavour effects can never be neglected in scalar triplet leptogenesis, even in the temperature regime where all charged lepton Yukawa interactions are out of equilibrium. This is at variance with the standard leptogenesis scenario with heavy Majorana neutrinos. In particular, the so-called single flavour approximation leads to predictions for the baryon asymmetry of the universe that can differ by a large a…
We study thermal leptogenesis induced by decays of a scalar SU(2)_L triplet. Despite the presence of gauge interactions, unexpected features of the Boltzmann equations make the efficiency close to maximal in most of the parameter space. We derive the maximal CP asymmetry in triplet decays, assuming that it is generated by heavier sources of neutrino masses: in this case successful leptogenesis needs a triplet heavier than 2.8 10^{10} GeV and does not further restrict its couplings, allowing detectable mu --> e gamma, tau --> mu gamma rates in the context of supersymmetric models. Triplet masse…
We extend the standard model by three types of inert fields including Majorana fermion singlets/triplets, real Higgs singlets/triplets and leptonic Higgs doublets. In the presence of a softly broken lepton number and an exactly conserved Z_2 discrete symmetry, these inert fields together can mediate a one-loop diagram for a Majorana neutrino mass generation. The heavier inert fields can decay to realize a successful leptogenesis while the lightest inert field can provide a stable dark matter candidate. As an example, we demonstrate the leptogenesis by the inert Higgs doublet decays. We also pe…
Leptogenesis appears to be a viable alternative to account for the baryon asymmetry of the universe through baryogenesis. In this context, we consider a scenario in which the standard model is extended with $S_3$ and $Z_2$ symmetry in addition to the two scalar triplets, two scalar doublets and three right handed neutrinos. Presence of scalar triplets and right-handed neutrinos in the scenarios of both type-I and type-II seesaw framework provide a different leptogenesis option and can help us to understand the matter-antimatter asymmetry with simple $S_3$ symmetry. We discuss the neutrino phen…
We consider the minimal supersymmetric triplet seesaw model as the origin of neutrino masses and mixing as well as of the baryon asymmetry of the Universe, which is generated through soft leptogenesis employing a CP violating phase and a resonant behavior in the supersymmetry breaking sector. We calculate the full gauge--annihilation cross section for the Higgs triplets, including all relevant supersymmetric intermediate and final states, as well as coannihilations with the fermionic superpartners of the triplets. We find that these gauge annihilation processes strongly suppress the resulting …
The leptogenesis with supersymmetric Higgs triplets is studied in the light of experimental verification in the TeV region. The lepton number asymmetry appears just after the inflation via multiscalar coherent evolution of Higgs triplets and antislepton on a flat manifold. If the Higgs triplet mass terms dominate over the negative thermal-log term for the Hubble parameter H comparable to the Higgs triplet mass M_Δ, the asymmetry is fixed readily to some significant value by the redshift and rotation of these scalar fields, providing the sufficient lepton-to-entropy ratio n_L / s \sim 10^-10. T…
In this paper, we consider the possibility of generating the observed baryon asymmetry of the Universe via leptogenesis in the context of triplet fermion mediated type-III seesaw model of neutrino mass. With a hierarchical spectrum of the additional fermions, the lower bound on the lightest triplet mass is $\sim 10^{10} {\rm~GeV}$ for successful leptogenesis, a couple of orders higher than that of the type-I case. We investigate the possibility of lowering this bound in the framework of two-Higgs-doublet models. We find that the bounds can be lowered down to $10^7$ GeV for a hierarchical spect…
We present and discuss constraints on supersymmetric type I seesaw models imposed by neutrino data, charged lepton flavor violation and thermal leptogenesis.
We study the thermal leptogenesis in the scenario where the standard model is extended to include one $SU(2)_{L}$ triplet Higgs boson, in addition to three generations of the right-handed neutrinos. And in the model we introduce the coupling between the Quintessence and the right-handed neutrinos, the triplet Higgs boson, so that the light neutrino masses vary during the evolution of the universe. Assuming that the lepton number asymmetry is generated by the decays of the lightest right-handed neutrino $N_{1}$, we find the thermal leptogenesis can be characterized by four model independent par…
We study the role played in leptogenesis by the equilibration of lepton flavors, as could be induced in supersymmetric models by off diagonal soft breaking masses for the scalar lepton doublets $\tilde m_{αβ}$, or more generically by new sources of lepton flavor violation. We show that if $\tilde m_{αβ}\gsim 1 $GeV and leptogenesis occurs below $\sim 100 $TeV, dynamical flavor effects are irrelevant and leptogenesis is correctly described by a one-flavor Boltzmann equation. We also discuss spectator effects in low scale leptogenesis by taking into account various chemical equilibrium condition…
We investigate a simple variant of type-II seesaw, responsible for neutrino mass generation, where the particle spectrum is extended with one singlet right-handed neutrino and an inert Higgs doublet, both odd under an additional $Z_2$ symmetry. While the role of the dark matter is played by the lightest neutral component of the inert Higgs doublet, its interaction with the Standard Model lepton doublets and the right-handed neutrino turns out to be crucial in generating the correct baryon abundance of the Universe through flavored leptogenesis from the decay of the $SU(2)_L$ scalar triplet, in…
We propose a UV completion of the inverse see-saw scenario using fermion SU(2) triplet representations. Within this framework, a variation of the standard thermal leptogenesis is achievable at the O(TeV) scale, owing to the presence of a viable dark matter candidate. This baryogenesis scenario is ruled out if a triplet fermion is observed at the LHC. The dark matter is given by the lightest neutral component of a complex scalar SU(2) triplet, with mass in the TeV range. The scalar sector, which is enriched in order to account for the small neutrino masses, is treated in detail and shows potent…
We study a model for leptogenesis in which the total CP asymmetries in the decays and scatterings involving the SU(2) singlet seesaw neutrinos $N_α$ vanish ($ε_{N_α}=0$). Leptogenesis is possible due to non-vanishing CP violating lepton flavor asymmetries, realizing a situation in which the baryon asymmetry is due exclusively to flavor effects. We study the production of a net lepton asymmetry by solving the Boltzmann equations specific to this model, and we show that successful leptogenesis can be obtained at a scale as low as the TeV. We also discuss constraints on the model parameter space …
In models with flavor symmetries in the leptonic sector leptogenesis can take place in a very different way compared to the standard leptogenesis scenario. We study the generation of a $B-L$ asymmetry in these kind of models in the flavor symmetric phase pointing out that successful leptogenesis requires (i) the right-handed neutrinos to lie in different representations of the flavor group; (ii) the flavons to be lighter at least that one of the right-handed neutrino representations. When these conditions are satisfied leptogenesis proceeds due to new contributions to the CP violating asymmetr…
I study variations of the standard leptogenesis scenario that can arise if an additional mass scale related to the breaking of some new symmetry is present below the mass $M_{N_1}$ of the lightest right-handed Majorana neutrino. I present a particular realization of this scheme that allows for leptogenesis at the TeV scale. In this realization the baryon asymmetry is exclusively due to flavor effects.
We argue that ΔL=2 neutrino spin flavor precession, induced by the primordial magnetic fields, could have a significant impact on the leptogenesis process that accounts for the baryon asymmetry of the universe. Although the extra galactic magnetic fields is extremely weak at present time (about 10^{-9} Gauss), the primordial magnetic filed at the electroweak scale could be quite strong (of order 10^{17} Gauss). Therefore, at this scale, the effects of the spin flavor precession are not negligible. We show that the lepton asymmetry may be reduced by 50% due to the spin flavor precession. In add…
We consider a smooth hybrid inflation scenario based on a supersymmetric SU(2)_L x SU(2)_R x U(1)_B-L model. The Higgs triplets involved in the model play a key role in inflation as well as in explaining the observed baryon asymmetry of the universe. We show that the baryon asymmetry can originate via non-thermal triplet leptogenesis from the decay of SU(2)_L triplets, whose tiny vacuum expectation values also provide masses for the light neutrinos.
A supersymmetric see-saw model obeying the flavor symmetry L_mu - L_tau, which naturally predicts quasi-degenerate neutrinos, is investigated. Breaking of the symmetry is introduced in the Dirac mass matrix because it is the most economic choice in the sense that all interesting low and high energy phenomenology is made possible: we analyze the predictions for the low energy neutrino observables, for leptogenesis and for lepton flavor violating decays such as mu \to e gamma, where the SPS benchmark points for the SUSY parameters are used. It is outlined how these decays in connection with the …
Lepton flavor violating processes such as μ\to 3e and μ\to e γare investigated with supersymmetric Higgs triplet pair Δand \bar Δin the light of neutrino masses and experimentally verifiable leptogenesis. The Higgs triplet mass M_Δis expected to be in the range of 1 - 100 TeV. The branching ratios of these charged lepton decays are evaluated in terms of M_Δand the coupling f L ΔL of Higgs triplet Δwith lepton doublet pairs L L, which is proportional to the neutrino mass matrix. They may be reached in the future collider experiments. In particular, the μ\to 3e decay would be observed indicating…
We review recent developments in leptogenesis on flavor effects. Their account discloses an important connection between the matter-antimatter asymmetry of the Universe and CP violation at low energies. Besides, they modify the upper bound on the neutrino masses holding in the unflavored case. In this respect, it is important to identify the exact condition for flavor effects to be relevant and for the `fully flavored' Boltzmann equations to be valid.
We study an extension of the supersymmetric standard model including a pair of electroweak triplet Higgs $Δ$ and ${\bar Δ}$. The neutrinos acquire Majorana masses mediated by these triplet Higgs fields rather than the right-handed neutrinos. The successful leptogenesis for baryogenesis can be realized after the inflation through the Affleck-Dine mechanism on a flat manifold consisting of $Δ$, ${\bar Δ}$, ${\tilde e}^c$ (anti-slepton), even if the triplet Higgs mass $M_Δ$ is much larger than the gravitino mass $m_{3/2} \sim 10^3 {\rm GeV}$. Specifically, due to the effects of the potential term…
Dirac leptogenesis (or Dirac neutrinogenesis), in which neutrinos are purely Dirac particles, is an interesting alternative to the standard leptogenesis scenario. In its supersymmetric version, the modified form of the superpotential required for successful baryogenesis contributes new, generically non-flavor-diagonal terms to the slepton and sneutrino mass matrices. In this work, we examine how current experimental bounds on flavor-changing effects in the lepton sector (and particularly the bound on Mu -> e Gamma) constrain Dirac leptogenesis and we find that it is capable of succeeding with …
The presence of flavor symmetries in the lepton sector may have several consequences for the generation of the baryon asymmetry of the Universe via leptogenesis. We review the mechanism in general type-I, type-II and type-III seesaw models. We then turn to the discussion of the cases when the asymmetry is generated in the context of seesaw models extended with flavor symmetries, before or after flavor symmetry breaking. Finally we explain how the interplay between type-I and type-II seesaws can (or not) lead to viable models for leptogenesis even when there is an exact mixing pattern enforced …
We study the constraints on a minimal supersymmetric seesaw model imposed by neutrino data, charged lepton flavor violation, thermal leptogenesis and perturbativity. We show that it is possible to constrain the three heavy Majorana neutrino masses as well as the complex Yukawa coupling matrix. Our results provide a first step towards a seesaw benchmark model for further phenomenological studies and model building.
I suggest a new particle model to integrate the fermion flavor, the TeV scale Leptogenesis and cold dark matter. The model has a local gauge symmetry $U(1)_{B-L}$ at the TeV scale and a flavor family symmetry SO(3), in addition, it also contains the fourth generation fermions in which including a cold dark matter neutrino. The model can simultaneously account for the fermion masses and flavor mixings, and the baryon asymmetry and cold dark matter. It not only excellently fits all the current experimental data, but also predicts some new results which are promising to be test in future experime…
We study how lepton flavor violation (LFV) is related to the reactor angle $θ_{13}$, LHC/dark matter (DM) signal with a successful leptogenesis in a radiative seesaw model through $A_4$ flavor symmetry breaking, in the light of the deviation of tri-bimaximal mixing (TBM) angles and the recent precision oscillation data. To do this, we consider the normal mass spectrum of light neutrino giving a successful leptogenesis at electroweak (EW) scale or more with a relatively large $\sinθ_{13}\simeq{\cal O}(0.1)$, where a successful leptogenesis requires LHC/DM signal $m_{-}\lesssim$ a few keV in our…
The neutral component of an inert scalar multiplet with hypercharge can provide a stable dark matter particle when its real and imaginary parts have a splitting mass spectrum. Otherwise, a tree-level dark matter-nucleon scattering mediated by the $Z$ boson will be much above the experimental limit. In this paper we focus on a mixed inert scalar triplet dark matter scenario where a complex scalar triplet with hypercharge can mix with another real scalar triplet without hypercharge through their renormalizable coupling to the standard model Higgs doublet. We consider three specified cases that c…
The See-Saw mechanism provides a nice way to explain why neutrino masses are so much lighter than their charged lepton partners. It also provides a nice way to explain baryon asymmetry in our universe via the leptogenesis mechanism. In this talk we review leptogenesis and LHC physics in a See-Saw model proposed in 1989, now termed the Type III See-Saw model. In this model, $SU(2)_L$ triplet leptons are introduced with the neutral particles of the triplets playing the role of See-Saw. The triplet leptons have charged partners with standard model gauge interactions resulting in many new features…
We consider leptogenesis in a minimal S_3 extension of the standard model with an additional Z_2 symmetry in the leptonic sector. It is found that the CP phase appearing in the neutrino mixing is the same as that for the CP asymmetries responsible for leptogenesis. Because of the discrete S_3 x Z_2 flavor symmetries, the CP asymmetries are strongly suppressed. We therefore assume that the resonant enhancement of the CP asymmetries takes place to obtain a realistic size of baryon number asymmetry in theuniverse. Three degenerate right-handed neutrino masses of O(10) TeV are theoretically expect…
Towards Testable Type-III Leptogenesis in Non-Standard Early Universe Scenarios
Department of Physics and Astronomical Science, Central University of Himachal Pradesh（喜马偕尔邦中央大学物理与天文科学系）；Department of Physics, Pragjyotish College（普拉吉约提什学院物理系）
We demonstrate a unified scenario for neutrino mass, baryon asymmetry, dark matter and inflation. In addition to a fermion triplet for the so-called minimal dark matter, we extend the standard model by three heavy fields including a scalar singlet, a fermion triplet and a fermion singlet/Higgs triplet. The heavy scalar singlet, which is expected to drive an inflation, and the dark matter fermion triplet are odd under an unbroken $Z_2^{}$ discrete symmetry, while the other fields are all even. The heavy fermion triplet offers a tree-level type-III seesaw and then mediates a three-body decay of …
We study leptogenesis from the out-of-equilibrium decays of the lightest heavy neutrino $N_1$ in the medium (low) temperature regime, $T\lsim 10^{12}$ GeV ($10^{10}$ GeV), where the rates of processes mediated by the $τ$ (and $μ$) Yukawa coupling are non negligible, implying that the effects of lepton flavors must be taken into account. We find important quantitative and qualitative differences with respect to the case where flavor effects are ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of magnitude; (ii) The sign of the asymmetry can be opposite to what one wou…
We investigated thermal leptogenesis scenarios in the left-right symmetric extension of the standard model. In the SO(10) GUT framework, we impose the D-parity realization below GUT scale. These two conditions makes our model more restrictive and predictive. In such a case, a D-parity odd singlet in the 4-index antisymmetric tensor representation of SO(10) have a critical role. This singlet have prospects of causing a very large mass hierarchy between SU(2)L and SU(2)R triplet scalars. We test our model by computing baryogenesis via leptogenesis. The heavy right-handed neutrinos N's and the SU…
We formulate three-flavor type-I leptogenesis in the $μτ$ basis which is convenient because in the three-flavor regime, both $μ$ and $τ$ charged lepton Yukawa interactions are in thermal equilibrium and the thermal bath is symmetric under the exchange $μ\leftrightarrow τ$. We apply this formalism to models with $μτ$-reflection $\mathsf{CP}^{μτ}$ symmetry. We confirm the previous result that leptogenesis fails in the three-flavor regime with exact $\mathsf{CP}^{μτ}$ symmetry. Allowing $\mathsf{CP}^{μτ}$ symmetry to be broken to various degrees, we show that leptogenesis can be successful in the…
We propose a minimal $A_4$ flavor symmetric model, assisted by $Z_2 \times Z_3$ symmetry, which can naturally takes care of the appropriate lepton mixing and neutrino masses via Type-I seesaw. It turns out that the framework, originated due to a specific flavor structure, favors the normal hierarchy of light neutrinos and simultaneously narrows down the range of Dirac CP violating phase. It predicts an interesting correlation between the atmospheric mixing angle and the Dirac CP phase too. While the flavor structure indicates an exact degeneracy of the right handed neutrino masses, renormaliza…
We study thermal leptogenesis from decays of the electroweak triplets that mediate neutrino masses in type-II and type-III see-saw. We find that Sommerfeld corrections reduce the baryon asymmetry by ~30%, and that successful leptogenesis needs triplets heavier than 1.6 TeV, beyond the discovery reach of LHC.
Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed neutrinos or extra triplets, it also provides a compelling framework for baryogenesis via leptogenesis. We derive in this context the full network of Boltzmann equations for studying leptogenesis in the flavored regime. To this end we determine the relations which hold among the chemical potentials of the various particle species in the thermal bath. This takes into account the SM Yukawa intera…
Recently it has been found that introducing a triplet Higgs to the standard model could provide a feasible leptogenesis to generate the baryon asymmetry of our universe, providing that the inflation is driven by the mixing state of the triplet Higgs and SM Higgs. In this work, we survey the viable parameter space satisfying the vacuum stability and perturbativity in this model. We find that the introduction of the triplet Higgs would also ameliorate the problem of the Higgs vacuum instability. We present two representative parameter regions where the origin of neutrino masses, baryon asymmetry…
We have proposed a new minimal extension of the Standard Model with a heavy Majorana fermion triplet($Σ$) and an extra scalar doublet($η$) so that the seesaw mechanism is radiative and can be accessible at upcoming accelerators. The origin of neutrino mass via the famous seesaw mechanism through the heavy Majorana fermion triplet has been discussed. We have proposed a mechanism of leptogenesis by the decay of the lightest neutral component of the fermion triplet into a Standard Model lepton doublet and an extra Higgs doublet. The important thing is that the leptogenesis scenario discussed in t…
We propose a simple ansatz for neutrino phenomenology, in which the relevant lepton mass matrices take the universal Fritzsch-like form and the seesaw relation holds under a particular condition. There exist six textures of this nature, but their consequences on neutrino oscillations are exactly the same. We show that our scenario is viable to account for the cosmological baryon number asymmetry via thermal leptogenesis. Its predictions for the lepton-flavor-violating decays μ-> eγ, tau -> μγand τ-> eγare also presented. We find that the branching ratios of these rare processes depend strongly…
In this paper, we consider a chaotic inflation model where the role of inflaton is played by the Higgs triplet in type II seesaw mechanism for generating the small masses of left-handed neutrinos. Leptogenesis could happen after inflation. This model is constructed without introducing supersymmetry (SUSY).
We investigate the resonant leptogenesis scenario in the minimally $U(1)_{B-L}$ extended standard model with minimal flavor violation. In our model, the $U(1)_{B-L}$ gauge symmetry is broken at the TeV scale and standard model singlet neutrinos gain Majorana masses of order TeV. In addition, we introduce a flavor symmetry on the singlet neutrinos at a scale higher than TeV. The flavor symmetry is explicitly broken by the neutrino Dirac Yukawa coupling, which induces splittings in the singlet neutrino Majorana masses at lower scales through renormalization group evolutions. We call this setup "…
In thermal leptogenesis, the cosmic matter-antimatter asymmetry is produced by CP violation in the decays N --> l + Φof heavy right-handed Majorana neutrinos N into ordinary leptons l and Higgs particles Φ. If some charged-lepton Yukawa couplings are in equilibrium during the leptogenesis epoch, the l interactions with the background medium are flavor sensitive and the coherence of their flavor content defined by N --> l+Φis destroyed, modifying the efficiency of the inverse decays. We point out, however, that it is not enough that the flavor-sensitive processes are fast on the cosmic expansio…
We investigate a flavored washout effect due to the decay of the lightest right-handed neutrino, assuming that there is non-vanishing initial lepton asymmetry and the decay of the lightest right-handed neutrinos gives negligible contribution to the asymmetry. We figure out general features of the washout effect. It is shown that there is a novel parameter region where an effect that is negligible in most cases plays a critical role and a sizable lepton asymmetry can survive against the washout process even in a strong washout region.
