We have shown that non-zero U_{e3} is generated in a see-saw type softly broken A_4 symmetric model through a single parameter perturbation in m_D in a single element. We have explored all possible 9 cases to study the neutrino mixing angles considering the best fitted values of Δm_{\odot}^2 and Δm_{atm}^2 with all parameters real. We have extended our analysis for the complex case and demonstrated large low energy CP violation (J_{CP}\simeq 10^{-2}) and m_{ee} in addition to mixing and mass pattern. We have also investigated leptogenesis and for a reasonable choice of model parameters compatible with low energy data, WMAP value of baryon asymmetry 6\times 10^{-10} is obtained for right handed neutrino mass scale M_0\simeq 10^{13} GeV. We have obtained a relation among the phases responsible for leptogenesis and have shown that these phases also have correlations with low energy CP violating phases.
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…
In some classes of flavour models based on unified theories with a type I see-saw mechanism, the prediction for the mass of the lightest right-handed neutrino is in conflict with the lower bound from the requirement of successful thermal leptogenesis. We investigate how lifting the absolute neutrino mass scale by adding a type II see-saw contribution proportional to the unit matrix can solve this problem. Generically, lifting the neutrino mass scale increases the prediction for the mass of the lightest right-handed neutrino while the decay asymmetry is enhanced and washout effects are reduced,…
Neutrino oscillations data indicates that neutrino mixings are consistent with an apparent $ν_μ- ν_τ$ exchange symmetry in neutrino mass matrix. We observe that in the mininimally extended standard model with the see-saw mechanism, one can impose $μ\leftrightarrowτ$ symmetry at the tree level on all Lagrangian terms, but for the mass difference among $μ$ and $τ$ leptons. In the absence of any new extra physics, this mass difference becomes the only source for the breaking of such a symmetry, which induces, via radiative corrections, small but predictable values for $θ_{13}$, and for the deviat…
We analyze the most general version of the supersymmetric minimal see-saw model with only two right-chiral neutrinos which are degenerate in masses at the scale of Grand Unification. We study the renormalization effects that give rise to non-zero CP asymmetries in the decays of these neutrinos and find that their resonant enhancement due to small mass splitting is partly compensated by other RG effects in the running of the neutrino Yukawa couplings. In spite of this compensation, the CP asymmetries can be large enough for successful thermal leptogenesis. Moreover, they depend very weakly on t…
In the Type I see-saw model, the naturalness requirement that corrections to the electroweak $μ$ parameter not exceed 1 TeV results in a rough bound on the lightest right-handed neutrino mass, $M_{N_1}\lesssim 3\times 10^7$ GeV. In this letter we derive generic bounds applicable in any three-flavour Type I see-saw model. We find $M_{N_1}\lesssim 4\times 10^7$ GeV and $M_{N_2}\lesssim 7\times 10^7$ GeV. In the limit of one massless neutrino, there is no naturalness bound on $M_{N_3}$ in the Poincare protected decoupling limit. Our results confirm that no Type I see-saw model can explain the obs…
In this paper, we derive the relationship between the weak basis invariants (WB) related to CP violation responsible for leptogenesis and CP violation relevant at low energy. We examine all the experimental viable cases of Frampton-Glashow and Yanagida (FGY) model, in order to construct the WB invariants in terms of left handed Majorana neutrino mass matrix elements, and thus finding the necessary and sufficient condition for CP conservation. Further for all the viable FGY texture zeros, we have shown the explicit dependence of WB invariants on Dirac type and Majorana type CP violating phases.…
The presence of the triplet $Δ_{L}$ in left-right symmetric theories leads to type-II see-saw mechanism for the neutrino masses. In these models, assuming a normal mass hierarchy for the heavy Majorana neutrinos, we derive a lower bound on the mass of the lightest of heavy Majorana neutrino from the leptogenesis constraint. From this bound we establish a consistent picture for the hierarchy of heavy Majorana neutrinos in a class of left right symmetric models in which we identify the neutrino Dirac mass matrix with that of Fritzsch type charged lepton mass matrix. It is shown that these values…
We consider the see-saw mechanism for hierarchical Dirac and Majorana neutrino mass matrices m_D and M_R, including the CP violating phases. Simple arguments about the structure of the neutrino mass matrix and the requirement of successful leptogenesis lead to the situation that one of the right-handed Majorana neutrinos is much heavier than the other two, which in turn display a rather mild hierarchy. It is investigated how for the neutrino mixing one small and two large angles are generated. The mixing matrix element |U_{e3}|^2 is larger than 10^{-3} and a characteristic ratio between the br…
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…
The related issues of Majorana CP violation in the lepton sector and leptogenesis are investigated in detail in two rather generic supersymmetric models with type I see-saw mechanism of neutrino mass generation and A_4 flavour symmetry, which naturally lead at leading order to tri-bimaximal neutrino mixing. The neutrino sector in this class of models is described at leading order by just two real parameters and one phase. This leads, in particular, to significant low energy constraints on the Majorana phases α_{21} and α_{31} in the PMNS matrix, which play the role of leptogenesis CP violating…
We discuss non-perturbative corrections to the neutrino sector, in the context of a D-brane Pati-Salam-like model, that can be obtained as a simple alternative to $SO(10)$ GUT's in theories with open and unoriented strings. In such D-brane models, exotic stringy instantons can correct the right-handed neutrino mass matrix in a calculable way, thus affecting mass hierarchies and modifying the see-saw mechanism to what we name exotic see-saw. For a wide range of parameters, a compact spectrum of right-handed neutrino masses can occur that gives rise to a predictive scenario for low energy observ…
A possible interplay of both terms in the type II see-saw formula is illustrated by presenting a novel way to generate deviations from exact bimaximal neutrino mixing. In type II see-saw mechanism with dominance of the non-canonical SU(2)_L triplet term, the conventional see-saw term can give a small contribution to the neutrino mass matrix. If the triplet term corresponds to the bimaximal mixing scheme in the normal hierarchy, the small contribution of the conventional see-saw term naturally generates non-maximal solar neutrino mixing. Atmospheric neutrino mixing is also reduced from maximal,…
The LFV charged lepton decays mu to e + gamma, tau to e + gamma and tau to mu + gamma and thermal leptogenesis are analysed in the MSSM with see-saw mechanism of neutrino mass generation and soft SUSY breaking with universal boundary conditions. The case of hierarchical heavy Majorana neutrino mass spectrum, M_1 << M_2 << M_3, is investigated. Leptogenesis requires M_1 > 10^9 GeV. Considering the natural range of values of the heaviest right-handed Majorana neutrino mass, M_3 > 5*10^{13} GeV, and assuming that the soft SUSY breaking universal gaugino and/or scalar masses have values in the ran…
In this present work, we uphold the standard model (SM) augmented with two right-handed (RH) neutrinos along with two singlet neutral fermions to generate active neutrino masses via (2,2) inverse see-saw mechanism. All entries of the neutrino mass matrix are taken to be complex to make this study a general one. We also investigate if the parameter points compatible with the neutrino oscillation data simultaneously satisfy the experimental bounds coming from the lepton flavour violating (LFV) decays : $μ\to e γ,~ τ\to e γ, ~ τ\to μγ$. This study also explores the prospect of producing the baryo…
We study constraints on neutrino properties from texture zeros in bi-large mixing See-Saw mass matrix and also from leptogenesis. Texture zeros may occur in the light (class a)) or in the heavy (class b)) neutrino mass matrices. Each of these two classes has 5 different forms which can produce non-trivial three generation mixing with at least one texture zero. We find that two types of texture zero mass matrices in both class a) and class b) can be consistent with present data on neutrino masses, mixing and produce the observed baryon asymmetry of the universe. None of the neutrinos can have z…
A novel scenario of leptogenesis is investigated in the supersymmetric neutrino see-saw model. The right-handed sneutrino $ {\tilde N} $ and the $ ϕ$ field in the $ {\tilde L} H_u $ direction of the slepton and Higgs doublets start together coherent evolution after the inflation with right-handed neutrino mass $ M_N $ smaller than the Hubble parameter of inflation. Then, after some period the motion of $ {\tilde N} $ and $ ϕ$ is drastically changed by the cross coupling $ M_N h_ν{\tilde N}^* ϕϕ$ from the $ M_N N N $ and $ h_νN L H_u $ terms, and the significant asymmetries of $ {\tilde N} $ an…
In the light of recent discovery of nonzero $θ_{13}$, we have analyzed the Altarelli-Feruglio $A_4$ flavor symmetry model extended with additional flavon. The inclusion of the new field leads to the deviation from exact tri-bimaximal neutrino mixing pattern in the context of type-I see-saw by producing a nonzero $θ_{13}$ consistent with the recent experimental results at the leading order. A sum rule for light neutrino masses is also obtained in this context. The set-up constraints the two Majorana phases involved in the lepton mixing matrix in terms of $A_4$ parameter space. We have shown tha…
We discuss the relation between leptogenesis and the MNS phases in the class of see-saw models called light sequential dominance in which the right-handed neutrinos dominate sequentially, with the dominant right-handed neutrino being the lightest one. The heaviest right-handed neutrino then decouples, leaving effectively two right-handed neutrinos. Light sequential dominance is motivated by SO(10) models which predict three right-handed neutrinos. With an approximate Yukawa texture zero in the 11 position there are only two see-saw phases which are simply related to the MNS phase measurable at…
The see-saw mechanism to generate small neutrino masses is reviewed. After summarizing our current knowledge about the low energy neutrino mass matrix we consider reconstructing the see-saw mechanism. Low energy neutrino physics is not sufficient to reconstruct see-saw, a feature which we refer to as ``see-saw degeneracy''. Indirect tests of see-saw are leptogenesis and lepton flavor violation in supersymmetric scenarios, which together with neutrino mass and mixing define the framework of see-saw phenomenology. Several examples are given, both phenomenological and GUT-related. Variants of the…
Assuming only a hierarchical structure of the heavy Majorana neutrino masses and of the neutrino Dirac mass matrix m_D of the see-saw mechanism, we find that in order to produce the observed baryon asymmetry of the Universe via leptogenesis, the scale of m_D should be given by the up-quark masses. Lepton flavor violating decays μ\to e + γ, τ\to μ+ γand τ\to e + γare considered and a characteristic relation between their decay rates is predicted. The effective Majorana mass in neutrinoless double beta decay depends on the CP violating phase controlling the leptogenesis if one of the heavy Major…
The running of neutrino parameters in see-saw models and its implications for leptogenesis and for testing predictions of mass models with future precision experiments are discussed using analytical approximations as well as numerical results.
Neutrino Physics is a mature branch of science with all the three neutrino mixing angles and two mass squared differences determined with high precision. Inspite of several experimental verifications of neutrino oscillations and precise measurements of two mass squared differences and the three mixing angles, the unitarity of the leptonic mixing matrix is not yet established, leaving room for the presence of small non-unitarity effects. Deriving the bounds on these non-unitarity parameters from existing experimental constraints, on cLFV decays such as, $ μ\rightarrow eγ$, $ μ\rightarrow τγ$, $…
In models with flavour symmetries added to the gauge group of the Standard Model the CP-violating asymmetry necessary for leptogenesis may be related with low-energy parameters. A particular case of interest is when the flavour symmetry produces exact Tri-Bimaximal lepton mixing leading to a vanishing CP-violating asymmetry. In this paper we present a model-independent discussion that confirms this always occurs for unflavoured leptogenesis in type I see-saw scenarios, noting however that Tri-Bimaximal mixing does not imply a vanishing asymmetry in general scenarios where there is interplay be…
Motivated by the recent results from Daya Bay, Reno and Double Chooz Collaborations, we study the consequences of small departures from exact $μ-τ$ symmetry in the neutrino sector, to accommodate a non-vanishing value of the element $V_{e3}$ from the leptonic mixing matrix. Within the see-saw framework, we identify simple patterns of Dirac mass matrices that lead to approximate $μ-τ$ symmetric neutrino mass matrices, which are consistent with the neutrino oscillation data and lead to non-vanishing mixing angle $V_{e3}$ as well as precise predictions for the CP violating phases. We also show th…
In this talk we show how a natural neutrino mass hierarchy can follow from the type I see-saw mechanism, and a natural neutrino mass degeneracy from the type II see-saw mechanism, where the bi-large mixing angles can arise from either the neutrino or charged lepton sector. We summarize the phenomenological implications of such natural models, and discuss the model building applications of the approach, focussing on the $SU(3)\times SO(10)$ model. We also show that in such type II models the leptogenesis asymmetry parameter becomes proportional to the neutrino mass scale, in sharp contrast to t…
The masses and mixing of the light left-handed neutrinos can be related to those of the heavy right-handed neutrinos in left-right symmetric theories. Properties of the light neutrinos are measured in terrestrial experiments and the CP-violating decays of their heavy counterparts produce a baryon asymmetry via the well-known leptogenesis mechanism. The left-handed Higgs triplet, present in left-right symmetric theories, modifies the usual see-saw formula. It is possible to relate the lepton asymmetry to the light neutrino parameters when the triplet and the top quark through the usual see-saw …
A discrepancy between the experimental and theoretical results was reported for the anomalous magnetic moment of the muon. In leptogenesis scenarios which are due to a decay of right-handed neutrinos, this anomaly leads to large violations of lepton flavour within the framework of supersymmetric see-saw models. It is shown that for a hierarchical right-handed neutrino mass spectrum, we generically expect to observe μ\to e γin the near future experiment.
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.
The minimal Type I see-saw model cannot explain the observed neutrino masses and the baryon asymmetry of the Universe via hierarchical thermal leptogenesis without ceding naturalness. We show that this conclusion can be avoided by adding a second Higgs doublet with $\tanβ\gtrsim 4$. The models considered naturally accommodate a SM-like Higgs boson, and predict TeV-scale scalar states and low- to intermediate-scale hierarchical leptogenesis with $10^3\text{ GeV}\lesssim M_{N_1}\lesssim 10^8\text{ GeV}$.
Leptogenesis in left-right symmetric theories is studied. The usual see-saw mechanism is modified by the presence of a left-handed Higgs triplet. A simple connection between the properties of the light left-handed and heavy right-handed neutrinos is found. Predictions of this scenario for neutrinoless double beta decay and terrestrial CP violation in long-baseline experiments are given. These observables can in principle distinguish different realizations of the model.
We explore low-scale leptogenesis in a class of supersymmetric SO(10) models using extra singlet neutrinos and the Higgs representations {126}_H\oplus {\ovl{126}}_H as well as {16}_H \oplus {\bar {16}}_H. A singlet neutrino, which can be as light as 10^5-10^6 GeV, decays through its small mixings with right-handed neutrinos creating a lepton asymmetry which is shown to be flavor dependent. While the doublet vacuum expectation value in {\ovl{16}}_H triggers the generation of desired mixings, it also induces a large RH triplet vev that breaks the LR intermediate gauge symmetry and gives large RH…
It is shown that the requirement of preservation of baryon asymmetry does not rule out a scale for leptogenesis as low as 10 TeV. The conclusions are compatible with see-saw mechanism if for example the pivot mass scale for neutrinos is $\approx 10^{-2}$ that of the charged leptons. We explore the parameter space $\tilde{m}_1$-$M_1$ of relevant light and heavy neutrino masses by solving Boltzmann equations. A viable scenario for obtaining baryogenesis in this way is presented in the context of gauged $B-L$ symmetry.
We propose an SO(10) grand unified theory which has the simplest Higgs structure discussed so far in the literature. We include only two Higgs scalars, a 210-plet and a 16-plet. In addition to the regular fermions we include one singlet, whose mass term breaks chiral symmetry, so that fermions can get masses. All fermions acquire see-saw masses, since there are no Higgs bi-doublets. Required neutrino masses with large mixing as well as leptogenesis are possible in this model.
The usual see-saw formula is modified by the presence of two Higgs triplets in left-right symmetric theories. The contribution from the left-handed Higgs triplet to the see-saw formula can dominate over the conventional one when the neutrino Dirac mass matrix is identified with the charged lepton or down quark mass matrix. In this case an analytic calculation of the lepton asymmetry, generated by the decay of the lightest right-handed Majorana neutrino, is possible. For typical parameters, the out-of-equilibrium condition for the decay is automatically fulfilled. The baryon asymmetry has the c…
We discuss the effect of the neutrino mass scale on baryogenesis via the out-of-equilibrium decay of the lightest right-handed (s)neutrinos in type II see-saw models. We calculate the type II contributions to the decay asymmetries for minimal scenarios based on the Standard Model and on the Minimal Supersymmetric Standard Model, where the additional direct mass term for the neutrinos arises from a Higgs triplet vacuum expectation value. The result in the supersymmetric case is new and we correct the previous result in the scenario based on the Standard Model. We confirm and generalize our resu…
We consider a model of dynamical neutrino masses via the see-saw mechanism. Nambu-Goldstone bosons (majorons) arise associated with the formation of the heavy right-handed majorana masses. These bosons then acquire naturally soft masses (become pNGB's) at loop level via the Higgs-Yukawa mass terms. These models, like the original neutrino pNGB quintessence schemes of the 1980's that proceed through the Dirac masses, are natural, have cosmological implications through mass varying neutrinos, long range forces, and provide a soft potential for dark energy. We further argue that these models can …
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 …
We show that the neutrino models, as suggested by Low, which have an additional Abelian family symmetry and a real Higgs singlet to the default see-saw do not hinder the possibility of successful thermal leptogenesis. For these models (neglecting radiative effects), we have investigated the situation of strong washout in both the one-flavor approximation and when flavor effects are included. The result is that while such models predict that theta_{13}=0 and that one light neutrino to be massless, they do not modify or provide significant constraints on the typical leptogenesis scenario where t…
Effects of the lightest neutrino mass in "flavoured" leptogenesis when the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana phases in the neutrino mixing matrix $U$ are discussed. The type I see-saw scenario with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The "orthogonal" parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix $R$, is employed. Results for light neutrino mass spectrum with normal and inverted ordering (hier…
The leptogenesis is studied in the neutrino mass matrix with two zeros, which reduces the number of independent phases of the CP violation. These texture zeros are decomposed into the Dirac neutrino mass matrix and the right-handed Majorana one in the see-saw mechanism. It is found that there are six textures for the Dirac neutrino mass matrix, among which one texture with three zeros has three phases, three textures with four zeros have two phases, and two textures with five zeros have only one phase in the basis with the real right-handed Majorana mass matrix. The relation between the leptog…
We explain why the see-saw picture and leptogenesis make it particularly interesting to find out whether neutrinos are their own antiparticles, and whether their oscillations violate CP.
We derive the most minimal see-saw texture from an extra-dimensional dynamics. It predicts theta_13 = 0.078 \pm 0.015 and m_ee = 2.6 \pm 0.4 meV. Assuming thermal leptogenesis, the sign of the CP-phase measurable in neutrino oscillations, together with the sign of baryon asymmetry, determines the order of heavy neutrino masses. Unless heavy neutrinos are almost degenerate, successful leptogenesis fixes the lightest mass. Depending on the sign of the neutrino CP-phase, the supersymmetric version of the model with universal soft terms at high scale predicts BR(mu --> e gamma) or BR(tau --> mu ga…
We consider the see-saw mechanism within a non-supersymmetric SO(10) model. By assuming the SO(10) quark-lepton symmetry, and after imposing suitable conditions that ensure that the right-handed (RH) neutrino masses are at most mildly hierarchical (compact RH spectrum) we obtain a surprisingly predictive scenario. The absolute neutrino mass scale, the Dirac and the two Majorana phases of the neutrino mixing matrix remain determined in terms of the set of already measured low energy observables, modulo a discrete ambiguity in the signs of two neutrino mixing angles and of the Dirac phase. The R…
The CP-violation necessary for the generation of the baryon asymmetry of the Universe in the "flavoured" leptogenesis scenario can arise from the "low energy" PMNS neutrino mixing matrix and/or from the "high energy" part of neutrino Yukawa couplings, which can mediate CP-violating phenomena only at some high energy scale. The possible interplay between these two types of CP-violation is discussed. The type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The analysis shows that there exist regions in the leptogenesis parameter space …
Our present work explores the possibility of neutrino mass generation through {\em Type-I see-saw} mechanism and provides an explanation of the baryon asymmetry of the Universe via thermal leptogenesis in the framework of $Z_3$-symmetric three Higgs doublet model (3HDM) augmented with three right-handed neutrinos. Here the thermal leptogenesis is initiated by the out-of-equilibrium decay of the lightest heavy neutrino $N_1$. The constraints arising out of the scalar sector put strong bound on the model parameter $\tan β$, which in turn takes part in the computation of the lepton asymmetry $ε$.…
Grand unified theories where the neutrino mass is given by Type II seesaw have the potential to provide interesting connections between the neutrino and charged fermion sectors. We explore the possibility of having a dominant Type II seesaw contribution in supersymmetric SO(10). We show that this can be achieved in the model where symmetry breaking is triggered by 54 and 45-dimensional representations, without the need for additional fields other than those already required to have a realistic charged fermion mass spectrum. Physical consequences, such as the implementation of the BSV mechanism…
The scaling hypothesis postulates proportionality of two columns of the Majorana neutrino mass matrix in the flavor basis. This Ansatz was shown to lead to an inverted hierarchy and U_{e3} = 0. We discuss theoretical and phenomenological properties of this hypothesis. We show that (i) the neutrino mass matrix with scaling follows as a consequence of a generalized mu-tau symmetry imposed on the type-I see-saw model; (ii) there exists a unique texture for the Dirac mass matrix m_D which leads to scaling for arbitrary Majorana matrix M_R in the context of the type-I see-saw mechanism; (iii) unlik…
We make an analytic and numerical study of leptogenesis in the framework of the (Supersymmetric) Standard Model plus the see-saw mechanism with a U(1) family symmetry and single right-handed neutrino dominance. In presenting our analytic and numerical results we make a clear distinction between the theoretically clean asymmetry parameter $ε_1$ and the baryon asymmetry $Y_B$. In calculating $Y_B$ we propose and use a fit to the solutions to the Boltzmann equations which gives substantially more reliable results than parametrisations previously used in the literature. Our results show that there…
It is well-known that thermal leptogenesis through the decays of the lightest right-handed neutrinos encounters serious difficulties when SO(10)-inspired mass conditions are imposed on the Dirac neutrino mass matrix and light neutrino masses are generated through the type I see-saw mechanism. We show that these can be circumvented when the production from the next-to-lightest right-handed neutrinos and flavor effects are properly taken into account. Some conditions on the low energy parameters have to be satisfied in order for inverse processes involving the lightest right-handed neutrino not …
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 sc…
We revisit leptogenesis in the minimal non-supersymmetric type I see-saw mechanism with two right-handed (RH) neutrinos, including flavour effects and allowing both RH neutrinos N_1 and N_2 to contribute, rather than just the lightest RH neutrino N_1 that has hitherto been considered. By performing scans over parameter space in terms of the single complex angle z of the orthogonal matrix R, for a range of PMNS parameters, we find that in regions around z \sim \pm π/2, for the case of a normal mass hierarchy, the N_2 contribution can dominate the contribution to leptogenesis, allowing the light…
Taking into account the recent progress in the understanding of the lepton flavour effects in leptogenesis, we investigate in detail the possibility that the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana CP-violating phases in the PMNS neutrino mixing matrix U, and thus is directly related to the low energy CP-violation in the lepton sector (e.g., in neutrino oscillations, etc.). We first derive the conditions of CP-invariance of the neutrino Yukawa couplings lambda in the see-saw Lagrangian, and of the complex…
If the expectation value of the right-handed (rhd) sneutrino comes to dominate the universe, its decay naturally leads to successful leptogenesis, as well as significant dilution of dangerous inflationary relics, such as the gravitino. The resulting baryon asymmetry is independent of other cosmological initial conditions. This attractive variant of leptogenesis requires at least one of the rhd neutrinos to have small Yukawa coupling and to have mass ~ 10^6 GeV, much smaller than the grand unified (GUT) scale. We show that these features naturally arise in the context of independently motivated…
We study the symmetric 2-zero texture of the neutrino mass matrix, which is obtained from the symmetric Dirac neutrino mass matrix with 2-zeros and right-handed Majorana neutrino mass matrix with the general form via the see-saw mechanism, for the SUSY SO(10) GUT model including the Pati-Salam symmetry. We show that the only one texture in our model, having degenerate mass spectrum for the 1st and 2nd generation of right-handed Majorana neutrino, can simultaneously explain the current neutrino experimental data, lepton flavor violating processes and baryon asymmetry of the Universe. Within suc…
Flavor effects in leptogenesis reduce the region of the see-saw parameter space where the final predictions do not depend on the initial conditions, the strong wash-out regime. In this case we show that the lowest bounds holding on the lightest right-handed (RH) neutrino mass and on the reheating temperature for hierarchical heavy neutrinos, do not get relaxed compared to the usual ones in the one-flavor approximation, M_1 (T_reh) \gtrsim 3 (1.5) x 10^9 GeV. Flavor effects can however relax down to these minimal values the lower bounds holding for fixed large values of the decay parameter K_1.…
The gravitino problem gives a severe constraint on the thermal leptogenesis scenario. This problem leads us to consider some alternatives to it if we try to keep the gravitino mass around the weak scale $m_{3/2} \sim 100$ GeV. We consider, in this paper, the non-thermal leptogenesis scenario in the framework of a minimal supersymmetric SO(10) model. Even if we start with the same minimal SO(10) model, we have different predictions for low-energy phenomenologies dependent on the types of seesaw mechanism. This is the case for leptogenesis: it is shown that the type-I see-saw model gives a consi…
We analyse within the "flavoured" leptogenesis scenario of baryon asymmetry generation, the interplay of the "low energy" CP-violation, originating from the PMNS neutrino mixing matrix $U$, and the "high energy" CP-violation which can be present in the matrix of neutrino Yukawa couplings, $λ$, and can manifest itself only in "high" energy scale processes. The type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The "orthogonal" parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix $R$,…
We make a general analysis of neutrino phenomenology for the case neutrino masses are generated by the see-saw mechanism with just two right handed neutrinos. We find general constraints on leptogenesis and lepton flavour violating processes. We also analyse the predictions following from a nontrivial texture zero structure.
