The possibility to explain the baryon asymmetry in the Universe through the leptogenesis mechanism in the context of Adjoint SU(5) is investigated. In this model the neutrino masses are generated through the Type I and Type III seesaw mechanisms, and the field responsible for the Type III seesaw, called rho_3, generates the B-L asymmetry needed to satisfy the observed value of the baryon asymmetry in the Universe. We find that the CP asymmetry originates only from the vertex correction, since the self-energy contribution is not present. When neutrino masses have a normal hierarchy, successful leptogenesis is possible for 10^{11} GeV < M_{ρ_3}^{NH} < 4 10^{14} GeV. When the neutrino hierarchy is inverted, the allowed mass range changes to 2 10^{11} GeV < M_{ρ_3}^{IH} < 5 10^{11} GeV. These constraints make possible to rule out a large part of the parameter space in the theory which was allowed by the unification of gauge interactions and the constraints coming from proton decay.
We discuss how leptogenesis can explain the observed baryon asymmetry and summarize attempts of testing leptogenesis. We first perform estimates and discuss the main physics, and later outline the techniques that allow to perform precise computations.
We discuss the baryogenesis via leptogenesis mechanism within the supersymmetric and nonsupersymmetric SO(10) models. We find that the nonsupersymmetric model, endowed with an intermediate scale, is generally favoured, unless some fine tuning occurs in the supersymmetric case.
Leptogenesis in supersymmetric model is discussed comprehensively and in detail. In the first half, we discuss several leptogenesis mechanisms by the decay of heavy right-handed neutrino, which include the standard thermal leptogenesis, leptogenesis via inflaton decay, and leptogenesis from the coherent oscillation of the right-handed sneutrino. In the second half, we perform a detailed analysis on the leptogenesis via the LHu flat direction (Affleck-Dine leptogenesis).
We present a new mechanism for baryogenesis: at preheating after inflation fermions acquire a varying mass by their coupling to a time dependent field. Their CP-violating mass matrix can generate a charge asymmetry to be transformed into a lepton asymmetry through decay into standard model particles and heavy Majorana neutrinos. In a concrete model of hybrid inflation we compare ``coherent baryogenesis'' with nonthermal leptogenesis by perturbative decay of the inflation condensates.
Baryogenesis by heavy-neutrino decay and sphaleron reprocessing of both baryon and lepton number is reconsidered, paying special attention to the flavour structure of the general evolution equations and developing an approximate but sufficiently accurate analytic solution to the prototype evolution equation. Two different models of neutrino masses are examined, based on an Abelian U(1) or a non-Abelian U(2) family symmetry. We show that a consistent picture of baryogenesis can emerge in both cases, although with significant differences.
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 review the production of the matter-antimatter asymmetry in the early Universe, that is baryogenesis, in out-of-equlibrium conditions induced by decays of heavy particles or by the presence of phase boundaries. The most prominent examples are given by leptogenesis and electroweak baryogenesis, respectively. For both cases, we derive the equations that govern the production of the asymmetries. We first use intuitive arguments based on classical fluid equations in combination with quantum-field-theoretical effects of CP-violation. As for a more thorough approach that is well-suited for system…
Right-handed neutrinos offer an elegant solution to two well established phenomena beyond the Standard Model (SM) - masses and oscillations of neutrinos, as well as the baryon asymmetry of the Universe. It is also a minimalistic solution since it requires only singlet Majorana fermions to be added to the SM particle content. If these fermions are nearly degenerate, the mass scale of right-handed neutrinos can be very low and accessible by the present and planned experiments. There are at least two well studied mechanisms of the low-scale leptogenesis: baryogenesis via oscillations and resonant…
An SO(10) grand unified model considered previously by the authors featuring lopsided down quark and charged lepton mass matrices is successfully predictive and requires that the lightest two right-handed Majorana neutrinons be nearly degenerate in order to obtain the LMA solar neutrino solution. Here we use this model to test its predictions for baryogenesis through resonant-enhanced leptogenesis. With the conventional type I seesaw mechanism, the best predictions for baryogenesis appear to fall a factor of three short of the observed value. However, with a proposed type III seesaw mechanism …
By demanding a compact spectrum for the right-handed neutrinos and an approximate quark-lepton symmetry inspired from SO(10) gauge unification (assuming a Dirac neutrino mass matrix close to the up quark mass matrix), we construct a {\it fine tuning} scenario for baryogenesis via leptogenesis. We find two solutions with a normal hierarchy, with the lightest neutrino mass $m_1$ different from zero, providing an absolute scale for the spectrum. In the approximations of the model, there are three independent CP phases : $δ_L$ (that we take of the order of the quark Kobayashi-Maskawa phase) and th…
In the context of GUT baryogenesis models, a well-known theorem asserts that CPT conservation and the unitarity of S-matrix require that the lowest order contribution that leads to the generation of a non-zero net CP-violation via the decay of a heavy particle must be to $\mathcal{O}({α_\slashed{B}}^3)$, where $α_\slashed{B}$ is a baryon number (B) violating coupling. We revisit this theorem (which holds for lepton number (L) violation, and hence for leptogenesis as well) and examine its implications for models where the particle content allows the heavy particle to also decay via modes which …
We investigate the consequences of a generalized $\mathbb{Z}_2\times\mathbb{Z}_2$ symmetry on a scaling neutrino Majorana mass matrix. It enables us to determine definite analytical relations between the mixing angles $θ_{12}$ and $θ_{13}$, maximal CP violation for the Dirac type and vanishing for the Majorana type. Beside the other testable predictions on the low energy neutrino parameters such as $ββ_{0ν}$ decay matrix element $|M_{ee}|$ and the light neutrino masses $m_{1,2,3}$, the model also has intriguing consequences from the perspective of leptogenesis. With the assumption that the req…
We investigate the influence of primordial perturbations of the energy density and space--time metric on the generation of the lepton and baryon asymmetries. In the weak and strong washout regimes baryon isocurvature perturbations with amplitudes of the same order as those of the CMB perturbations are generated on scales of order of the respective Hubble scale. They are, however, completely washed out by baryon and photon diffusion at the later stages of the universe's evolution.
Affleck-Dine leptogenesis after thermal inflation along the $LH_u$ direction requires $m_L^2+m_{H_u}^2 < 0$ up to the AD scale ($|L|\simeq |H_u|\sim 10^9$ GeV). We renormalised this condition from the AD scale to the soft supersymmetry breaking scale by solving the renormalisation group equations perturbatively in the Yukawa couplings to obtain a semi-analytic constraint on the soft supersymmetry breaking parameters. We also used a fully numerical method to renormalise the baryogenesis condition and constrained the Minimal Supersymmetric Cosmological Model using the resulting baryogenesis cond…
In this paper, we examine how gauge interactions can dilute the lepton asymmetry in lepton induced baryogenesis. Constraints imposed on Majorana masses keep this dilution at an acceptable level.
The evidence for neutrino oscillations leads to small neutrino masses, which can be realized by means of the seesaw mechanism. In this framework, baryogenesis may be achieved from leptogenesis.
We use $S_4$ discrete group to construct a neutrino flavour model which leads to $TM_1$ mixing and is consistent with the neutrino oscillation data. Using the model's constrained parameter space, we predict the values of Dirac $CP$ phase and the light neutrino mass as $-1<\sin δ<-0.9$ and $1.7<m_1 (\text{meV})<5.5$ respectively. We thoroughly examine the usefulness of this model in explaining the observed baryon asymmetry of the Universe. Near-maximal breaking of CP symmetry (arising due to the $\text{TM}_1$ constraint) helps us in generating adequate baryon asymmetry through leptogenesis. We …
A brief overview of the phenomenology related to the seesaw mechanism and the baryogenesis via leptogenesis is presented. In particular, it is explained how large but not maximal lepton mixing can be achieved within the type II seesaw mechanism. Moreover, the consequences for leptogenesis are explored, including flavor effects.
We bring the theoretical issue of whether two important cosmological demands, baryon asymmetry and degenerate neutrinos as hot dark matter, can be compatible in the context of the seesaw mechanism. To realize leptogenesis with almost degenerate Majorana neutrinos without severe fine-tuning of parameters, we propose the hybrid seesaw mechanism with a heavy Higgs triplet and right-handed neutrinos. Constructing a minimal hybrid seesaw model with SO(3) flavor symmetry for the neutrino sector, we show that the mass splittings for the atmospheric and solar neutrino oscillations which are consistent…
We investigate baryogenesis via leptogenesis and generation of neutrino masses and mixings through the Type I plus Type III seesaw plus an one-loop mechanism in the context of Renormalizable Adjoint SU(5) theory. One light neutrino remains massless, because the contributions of three heavy Majorana fermions ρ_0, ρ_3 and ρ_8 to the neutrino mass matrix are not linearly independent. However none of these heavy fermions is decoupled from the generation of neutrino masses. This opens a new range in parameter space for successful leptogenesis, in particular, allows for inverted hierarchy of the neu…
Particle-antiparticle perturbation superhorizon crossing: baryogenesis, leptogenesis, magnetogenesis and darkogenesis
ICRANet（国际相对论天体物理中心）；Sapienza University of Rome（罗马大学）；INFN, Sezione di Perugia（意大利国家核物理研究所佩鲁贾分部）；ICTP-AP, University of Chinese Academy of Sciences（中国科学院大学理论物理与应用物理研究中心）
Interactions that manifest themselves as lepton number violating processes at low energies in combination with sphaleron transitions typically erase any pre-existing baryon asymmetry of the Universe. We demonstrate in a model independent approach that the observation of neutrinoless double beta decay would impose a stringent constraint on mechanisms of high-scale baryogenesis, including leptogenesis scenarios. Further, we discuss the potential of the LHC to model independently exclude high-scale leptogenesis scenarios when observing lepton number violating processes. In combination with the ob…
Seven types of leptogenesis models which can lead to a successful explanation of baryogenesis are presented. Emphasis is put on the conditions which need to be fulfilled by the neutrino masses as well as by the heavy state masses. The model dependence of these conditions is discussed.
How is CP violation of low energy related to CP violation required from baryon number asymmetry ? We give an example which shows a direct link between CP violation of neutrino oscillation and baryogenesis through leptogenesis.
We propose an extension of the standard model (SM) by including a dark sector comprising of three generations of heavy right-handed neutrinos, a singlet scalar and a singlet Dirac fermion, where the latter two particles are stable and are viable candidates of dark matter (DM). In the early Universe, the CP-violating out-of-equilibrium decay of heavy right-handed neutrinos to singlet Dirac fermion and scalar in the dark sector generates a net DM asymmetry. The latter is then transported to the visible sector via a dimension eight operator which conserves $B-L$ symmetry and is in thermal equilib…
A framework based on an effective symmetry that is either G(224)= SU(2)_L x SU(2)_R xSU(4)^c or SO(10) has been proposed (a few years ago) that successfully describes the masses and mixings of all fermions including neutrinos, with seven predictions, in good accord with the data. Baryogenesis via leptogenesis is considered within this framework by allowing for natural phases (~ 1/20-1/2) in the entries of the Dirac and Majorana mass-matrices. It is shown that the framework leads quite naturally, for both thermal as well as non-thermal leptogenesis, to the desired magnitude for the baryon asymm…
I propose a new mechanism for baryogenesis, in which the out-of-equilibrium condition is not neccessary. When the electroweak symmetry is broken spontaneously, left-handed neutrinos may get Majorana masses containing $CP-$violating phases. This induces a lepton asymmetry spontaneously, which is then converted to a baryon asymmetry in the presence of the sphaleron field.
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 demon…
We review the scenario of baryogenesis through leptogenesis induced by the out-of-equilibrium decays of heavy neutrinos. We pay special attention to the resonant phenomenon of CP violation through mixing of two nearly degenerate heavy Majorana neutrinos and show how unitarity and CPT invariance is maintained within the resummation approach. An important consequence of this is that the leptogenesis scale may be as low as 1 TeV, even for models with universal Yukawa couplings. We briefly discuss the impact of finite temperature effects and low-energy constraints to the afore-mentioned mechanism …
The energy budget of the universe contains two components, dark matter and dark energy, about which we have much to learn. One should not forget, however, that the baryonic component presents its own questions for particle cosmology. In the context of cosmology, baryons would have annihilated with their antiparticles in the early universe, leaving a negligible abundance of baryons, in disagreement with that observed. In this general lecture, delivered at the SLAC 2004 Summer Science Institute, I provide an overview of the central issue and the general principles behind candidate models. I also…
Baryogenesis via leptogenesis provides an appealing mechanism to explain the observed baryon asymmetry of the Universe. Recent refinements in the understanding of the dynamics of leptogenesis include detailed studies of the effects of lepton flavors and of the role possibly played by the lepton asymmetries generated in the decays of the heavier singlet neutrinos $N_{2,3}$. A review of these recent developments in the theory of leptogenesis is presented.
We present a model of leptogenesis that preserves lepton number. The model maintains the important feature of more traditional leptogenesis scenarios: the decaying particles that provide the CP violation necessary for baryogenesis also provide the explanation for the smallness of the neutrino Yukawa couplings. This model clearly demonstrates that, contrary to conventional wisdom, neutrinos need not be Majorana in nature in order to help explain the baryon asymmetry of the universe.
We study the evolution of a cosmological baryon asymmetry in leptogenesis when the right-handed neutrinos are produced in inflaton decays. By performing a detailed numerical study over a broad range of inflaton-neutrino couplings we show that the resulting asymmetry can be larger by two orders of magnitude or more than in thermal leptogenesis, if the reheating temperature T_{RH} is of the same order as the right-handed neutrino mass M_1. Hence, the lower limit on the baryogenesis temperature obtained in thermal leptogenesis can be relaxed accordingly.
Quark-lepton symmetry has been shown to be inconsistent with baryogenesis via leptogenesis in natural schemes of the see-saw mechanism. Within the phenomenological approach of textures, we relax this strict symmetry and propose weaker conditions, namely models of the neutrino Dirac mass matrix $M_D$ which have the same hierarchy as the matrix elements of $M_u$. We call this guide-line generalized $hierarchical$ quark-lepton symmetry. We consider in detail particular cases in which the moduli of the matrix elements of $M_D$ are equal to those of $M_u$. Within the phenomenological approach of te…
We present a unified theory of inflation, neutrino mass, baryogenesis and dark matter where global lepton number symmetry and its breaking play a crucial role. The basic idea is to use a lepton number carrying complex scalar field as the inflaton as well as the field that implements Affleck-Dine (AD) leptogenesis. Dark matter is the massive majoron which is a pseudo-Goldstone boson, resulting from the spontaneous breaking of lepton number symmetry supplemented by explicit lepton number violation needed to implement AD leptogenesis. The magnitude of the resulting $n_B/s$ in the model is related…
Baryogenesis via leptogenesis provides an appealing mechanism to explain the observed baryon asymmetry of the Universe. Recent refinements in the understanding of the dynamics of leptogenesis include detailed studies of the effects of lepton flavors and of the role possibly played by the lepton asymmetries generated in the decays of the heavier singlet neutrinos $N_{2,3}$. In this talk I present a short review of these recent developments in the theory of leptogenesis.
We present here a novel and testable mechanism for leptogenesis, which is characterized by a purely thermal generation of lepton asymmetry via scalar decay. Guided by the thermal mass matrix diagonalization in the finite-temperature regime, we propose a scenario in which the baryon asymmetry is formulated in terms of the masses and mixing from hierarchical Dirac neutrinos, as well as a vacuum scale accountable for the sub-eV neutrino masses. This allows a natural and direct link between the high-scale \textit{CP} asymmetry and the low-energy Dirac \textit{CP}-violating phase without involved m…
Modifications to the Friedmann equation in brane cosmology can have important implications for early universe phenomena such as inflation and the generation of the baryon asymmetry. In the framework of braneworld cosmology, we discuss a mechanism for baryogenesis via leptogenesis in the supersymmetric context, where the sneutrino is responsible for both inflation and the generation of the baryon asymmetry in the universe.
Neutrino properties can play a crucial role in determining the matter-antimatter asymmetry of the universe if thermal leptogenesis is the correct solution to the baryogenesis problem. Owing to this, the study of neutrino models goes beyond the mere purpose of generating tiny neutrino masses, and it is natural to incorporate the puzzle of the cosmic baryon asymmetry. To this end, we have investigated several different extensions of the neutrino model based on the type I seesaw mechanism with particular emphasis on their leptogenesis implications.
We investigate baryogenesis via leptogenesis in $A_4$ flavor model within the paradigm of type-I and II seesaw mechanism resulting in magic neutrino mass matrix with broken $μ-τ$ symmetry in a minimal scenario with two right-handed neutrinos(2RHN). Additional $Z_3$ cyclic symmetry is employed to constrain the Yukawa structure of model. The type-II seesaw terms play crucial role in generating non-degenerate neutrino masses and non-zero $θ_{13}$ and contribute in baryogenesis. In particular, after the spontaneous symmetry breaking, the Yukawa couplings $y_{Δ_1}$ and $y_{Δ_3}$ are responsible for…
In this paper, we extend the analysis of a Pati-Salam subcritical hybrid $F$-term inflation model, proposed by two of us, by studying the reheating and the baryogenesis (via leptogenesis) of the model. This SUSY GUT model is able to fit low energy electroweak precision data, LHC data, $b$-physics data, in addition to inflation observables such as the tensor-to-scalar ratio and the scalar spectral index. The reheating mechanism of this model is instant preheating due to the bosonic and fermionic broad parametric resonance, while the baryon-to-entropy ratio is obtained from the CP asymmetric rig…
We calculate the baryonic asymmetry of the universe in the baryogenesis-via-leptogenesis framework, assuming first a quark-lepton symmetry and then a charged-neutral lepton symmetry. We match the results with the experimentally favoured range. In the first case all the oscillation solutions to the solar neutrino problem, except the large mixing matter solution, can lead to the allowed range, but with fine tuning of the parameters. In the second case the general result is quite similar. Some related theoretical hints are discussed.
Following a baryogenesis scenario proposed by Lazarides, Panagiotakopoulos and Shafi, we show how the observed baryon asymmetry can be explained via resonant leptogenesis in a class of supersymmetric models with an intermediate mass scale M_I<~10^9 GeV. It involves the out of equilibrium decay of heavy (<~M_I) right handed neutrinos at a temperature close to the TeV supersymmetry breaking scale. Such models can also resolve the MSSM mu problem.
Baryogenesis via leptogenesis is an attractive scenario that links the physics of right handed neutrino sector with the low energy neutrino data. In the light of current neutrino oscillation data we studied the bound on the mass scale ($M_1$) of lightest right handed neutrino ($N_1$) as well as their mass hierarchy ($M_2/M_1$ and $M_3/M_1$) from the leptogenesis constraint which we discussed in two different parts of the thesis. In part-I, we studied the canonical leptogenesis in a {\it thermal} scenario and hence the bound on $M_1$. It is shown that the mass scale of $N_1$ must satisfy the co…
A `new' scenario is proposed for baryogenesis. We show that delayed decay of coloured Higgs particles in grand unified theories may generate excess baryon number of the empirically desired amount, if the mass of the heaviest neutrino is in the range $0.02 {\rm eV}<m_{ν_3}< 0.8 {\rm eV}$, provided that neutrinos are of the Majorana type. The scenario accommodates the case of degenerate neutrino masses, in contrast to the usual leptogenesis scenario, which does not work when three neutrino masses are degenerate.
We show that the U(1)-prime models linked with the seesaw mechanism at TeV scale can lead to a successful baryogenesis through soft leptogenesis with a resonant behavior in the B parameter. Such a consideration constrains the Z-prime mass to be larger than 2-3 TeV depending on the seesaw scale and the spharelon rate. Together with multi-TeV Z-prime, large sneutrino-antisneutrino mixing and CP violating phenomena required by TeV leptogenesis could be searched for in future colliders by observing the distinct same-sign dilepton--dichargino as well as dislepton--diHiggs signatures.
In the baryogenesis via leptogenesis framework the baryonic asymmetry depends on lepton mass matrices. In a previous paper we used SO(10)-inspired mass matrices and we found few possibilities to obtain a sufficient level of asymmetry. In the present paper we use SU(5)-inspired mass matrices, which also allow to check the dependence of the baryonic asymmetry on Dirac neutrino masses. In particular, we find that the large mixing matter solution to the solar neutrino problem, which within SO(10) gives too small asymmetry, can now be favoured.
We propose a minimal and motivated extension of the Standard Model characterised by an approximate lepton number conservation, which is able to simultaneously generate neutrino masses and to account for a successful baryogenesis via leptogenesis. The sterile fermions involved in the leptogenesis process have masses at the GeV scale. We determine the viable parameter space that complies with both the neutrino and baryogenesis phenomenology, and analyse the different regimes for the generation of a lepton asymmetry in the early Universe (weak and strong-washout) in order to determine their testa…
Affleck-Dine (AD) mechanism for leptogenesis involves the cosmological evolution of a complex scalar field (AD field) that carries non-zero lepton number. We show how explicit lepton number breaking terms, which involve the AD field needed to implement this scenario combined with fermionic WIMP dark matter, can generate neutrino mass at the one loop level, thus providing a unified framework for solving four major puzzles of the standard model i.e. inflation, baryogenesis, dark matter and neutrino mass. We discuss some phenomenological implications of this model.
We show that novel paths to dark matter generation and baryogenesis are open when the Standard Model is extended with three sterile neutrinos $N_i$ and a charged scalar $δ^+$. Specifically, we propose a new production mechanism for the dark matter particle --a multi-keV sterile neutrino, $N_1$-- that does not depend on the active-sterile mixing angle and does not rely on a large primordial lepton asymmetry. Instead, $N_1$ is produced, via freeze-in, by the decays of $δ^+$ while it is in equilibrium in the early Universe. In addition, we demonstrate that, thanks to the couplings between the hea…
