Soft Leptogenesis Research Articles

Soft leptogenesis in the NMSSM with a singlet right-handed neutrino superfield

In this work, we explore soft leptogenesis in the NMSSM framework extended by a right-handed neutrino superfield. We calculate the CP asymmetry, ε, and find it to be non-zero at tree-level without using thermal effects for the final state particles. This is in contrast to soft leptogenesis in the MSSM extended by a right-handed neutrino superfield where thermal effects are essential. The difference arises due to the presence of a 3-body decay of the sneutrino in the NMSSM that violates lepton number at tree-level. Apart from this, we also find that ε ≠ 0 if the additional singlet scalar has a complex vacuum expectation value while all the other NMSSM parameters including the soft SUSY breaking ones relevant for CP asymmetry remain real. We estimate the order of magnitudes of these parameters to produce sufficient baryon asymmetry of the Universe.

NonthermalCPviolation in soft leptogenesis

Soft leptogenesis is a mechanism which generates the matter-antimatter asymmetry of the Universe via the out-of-equilibrium decays of heavy sneutrinos in which soft supersymmetry breaking terms play two important roles: they provide the required $CP$ violation and give rise to the mass splitting between otherwise degenerate sneutrino mass eigenstates within a single generation. This mechanism is interesting because it can be successful at the lower temperature regime $T\ensuremath{\lesssim}1{0}^{9}\text{ }\text{ }\mathrm{GeV}$ in which the conflict with the overproduction of gravitinos can possibly be avoided. In earlier works, the leading $CP$ violation is found to be nonzero only if finite temperature effects are included. By considering generic soft trilinear couplings, we find two interesting consequences: (1) the leading $CP$ violation can be nonzero even at zero temperature realizing nonthermal $CP$ violation, and (2) the $CP$ violation is sufficient even far away from the resonant regime allowing soft supersymmetry breaking parameters to assume natural values at around the TeV scale. We discuss phenomenological constraints on such scenarios and conclude that the contributions to charged lepton flavor violating processes are close to the sensitivities of present and future experiments.

Cuts, cancellations and the closed time path: The soft leptogenesis example

By including all leading quantum-statistical effects at finite temperature, we show that no net asymmetry of leptons and sleptons is generated from soft leptogenesis, save the possible contribution from the resonant mixing of sneutrinos. This result contrasts with different conclusions appearing in the literature that are based on an incomplete inclusion of quantum statistics. We discuss vertex and wave-function diagrams as well as all different possible kinematic cuts that nominally lead to CP-violating asymmetries. The present example of soft leptogenesis may therefore serve as a paradigm in order to identify more generally applicable caveats relevant to alternative scenarios for baryogenesis and leptogenesis, and it may provide useful guidance in constructing viable models.

Baryon asymmetry and dark matter from soft leptogenesis

The framework for soft leptogenesis minimally extended with a DM sector is studied. A heavy singlet neutrino superfield acts as the source for (s)lepton asymmetry and by coupling to the singlet DM superfield it produces a DM particle density through decays. The nature of DM generated is twofold depending on whether the Yukawa and DM couplings are either small or large. With sufficiently small Yukawa and DM couplings DM annihilations into MSSM particles are slow and as a consequence all DM particles form the DM component. The solutions to Boltzmann equations are given and the dependence between the DM masses and coupling are presented in this weak coupling regime. Also, the behavior of the efficiency of producing asymmetric DM is determined with weak couplings. We note that a different outcome arises if the couplings are larger because then the ADM component is dominant due to the effectiveness of DM decays into the MSSM sector.

LEPTOGENESIS FROM SOFT SUPERSYMMETRY BREAKING: SOFT LEPTOGENESIS

Soft leptogenesis is a scenario in which the cosmic baryon asymmetry is produced from a lepton asymmetry generated in the decays of heavy sneutrinos (the partners of the singlet neutrinos of the seesaw) and where the relevant sources of CP violation are the complex phases of soft supersymmetry-breaking terms. We explain the motivations for soft leptogenesis, and review its basic ingredients: the different CP-violating contributions, the crucial role played by thermal corrections, and the enhancement of the efficiency from lepton flavor effects. We also discuss the high temperature regime T > 107 GeV in which the cosmic baryon asymmetry originates from an initial asymmetry of an anomalous R-charge, and soft leptogenesis reembodies in R-genesis.

SOFT LEPTOGENESIS AND GRAVITINO DARK MATTER IN GAUGE MEDIATION

In gauge mediated SUSY breaking models, the gravitino is generally the lightest SUSY particle and can be a candidate for a dark matter. However the viable abundance of the gravitino requires rather low reheating temparature. With this low reheating temparature, it is difficult to explain the baryon asymmetry of the universe with thermal leptogenesis. We consider the extended scenario of the gauge mediation, which generates A-terms. In this extended scenario, soft leptogenesis works successfully with the low reheating temperature. Therefore we can explain the baryon asymmetry and gravitino dark matter simultaneously.

Early Universe effective theories: the soft leptogenesis and R-genesis cases

We discuss the effective theory appropriate for studying soft leptogenesis at temperatures T≳107 GeV. In this regime, the main source of the B−L asymmetry is the CP asymmetry of a new anomalous R-charge that couples to generalized anomalous electroweak processes. Baryogenesis thus occurs mainly through R-genesis, and with an efficiency that can be up to two orders of magnitude larger than in usual estimates. Contrary to common belief, a sizeable baryon asymmetry is generated also when thermal corrections to the CP asymmetries in sneutrino decays are neglected which, in soft leptogenesis, implies vanishing lepton-flavour CP asymmetries. We present general Boltzmann equations for soft leptogenesis that are valid in all temperature regimes.

Soft leptogenesis and gravitino dark matter in gauge mediation

We study soft leptogenesis in gauge mediated supersymmetry breaking models with an enhanced A-term for the right-handed neutrino. We find that this scenario can explain the baryon asymmetry of the present universe, consistently with the gravitino dark matter for a wide range of gravitino mass m3/2=O(MeV)–O(GeV). We also propose an explicit model which induces the necessary A-term for the right-handed neutrino.

Flavoured soft leptogenesis and natural values of the B term

We revisit flavour effects in soft leptogenesis relaxing the assumption of universality for the soft supersymmetry breaking terms. We find that with respect to the case in which the heavy sneutrinos decay with equal rates and equal CP asymmetries for all lepton flavours, hierarchical flavour configurations can enhance the efficiency by more than two orders of magnitude. This translates in more than three order of magnitude with respect to the one-flavour approximation. We verify that lepton flavour equilibration effects related to off-diagonal soft slepton masses are ineffective for damping these large enhancements. We show that soft leptogenesis can be successful for unusual values of the relevant parameters, allowing for $B\sim {\cal O}({\rm TeV})$ and for values of the washout parameter up to $m_{\rm eff}/m_* \sim 5\times 10^{3}$.

On the full Boltzmann equations for leptogenesis

We consider the full Boltzmann equations for standard and soft leptogenesis, instead of the usual integrated Boltzmann equations which assume kineticequilibrium for all species. Decays and inverse decays may be inefficient for thermalising the heavy-(s)neutrino distribution function, leading to significant deviations from kinetic equilibrium. We analyse the impact of using the full kinetic equations in the case of a previously generated lepton asymmetry, and find that the washout of this initial asymmetry due to the interactions of the right-handed neutrino is larger than when calculated via the integrated equations. We also solve the full Boltzmann equations for soft leptogenesis, where the lepton asymmetry induced by the soft SUSY-breaking terms in sneutrino decays is a purely thermal effect, since at T = 0 the asymmetry in leptons cancels the one in sleptons. In this case, we obtain that in the weak washout regime (K ≲ 1) the final lepton asymmetry can change up to a factor four with respect toprevious estimates.

Electron EDM and soft leptogenesis in supersymmetric [formula omitted] extension of the Standard Model

We analyze the connection between electric dipole moment of the electron and the soft leptogenesis in supersymmetric B – L extension of the Standard Model. In this model, the B – L symmetry is radiatively broken at TeV scale. Therefore, it is a natural framework for low scale seesaw mechanism and also for implementing the soft leptogenesis. We show that the phases of trilinear soft SUSY breaking couplings A, which are relevant for the lepton asymmetry, are not constrained by the present experimental bounds on electric dipole moment. As in the MSSM extended with right-handed neutrinos, successful leptogenesis requires small bilinear coupling B, which is now given by A N and B – L breaking VEVs. SUSY B – L model with non-universal A-terms such that A N = 0 while A ν ≠ 0 is a promising scenario for soft leptogenesis. The proposed EDM experiments will test this scenario in the future.

The Ir(relevance) of Initial Conditions in Soft Leptogenesis

We explore how the initial conditions affect the final lepton asymmetry in Soft Leptogenesis. It has been usually assumed that the initial state is a statistical mixture of sterile sneutrinos and anti-sneutrinos with equal abundances. We calculate the lepton asymmetry due to the most general initial mixture. The usually assumed equal mixture produces a small, but sufficient, lepton asymmetry which is proportional to the ratio of the supersymmetry breaking scale over the Majorana scale. A more generic mixture, still with equal contents of sneutrinos and anti sneutrinos, yields an unsuppressed lepton asymmetry. Mixtures of non equal contents of sneutrinos and anti sneutrinos result in a large lepton asymmetry too. While these results establish the robustness of Soft Leptogenesis and other mixing based mechanisms, they also expose their lack of predictive power.

On quantum effects in soft leptogenesis

It has been recently shown that quantum Boltzmann equations may be relevant forleptogenesis. Quantum effects, which lead to a time-dependent CP asymmetry,have been shown to be particularly important for resonant leptogenesis when theasymmetry is generated by the decay of two nearly degenerate states. In this work weinvestigate the impact of the use of quantum Boltzmann equations in the frameworkof ‘soft leptogenesis’ in which supersymmetry soft breaking terms give a smallmass splitting between the CP-even and CP-odd right-handed sneutrino states ofa single generation and provide the CP-violating phase to generate the leptonasymmetry.

Flavoured soft leptogenesis

We study the impact of flavour in ``soft leptogenesis'' (leptogenesis induced by soft supersymmetry breaking terms). We address the question of how flavour effects can affect the region of parameters in which successful soft leptogenesis induced by CP violation in the right-handed sneutrino mixing is possible. We find that for decays which occur in the intermediate to strong washout regimes for all flavours, the produced total $B-L$ asymmetry can be up to a factor ${\cal O}(30)$ larger than the one predicted with flavour effects being neglected. This enhancement, permits slightly larger values of the required lepton violating soft bilinear term.

SO(10) unified models and soft leptogenesis

Motivated by the fact that, in some realistic models combining SO(10) GUTs and flavour symmetries, it is not possible to achieve the required baryon asymmetry through the CP asymmetry generated in the decay of right-handed neutrinos, we take a fresh look on how deep this connection is in SO(10). The common characteristics of these models are that they use the see-saw with right-handed neutrinos, predict a normal hierarchy of masses for the neutrinos observed in oscillating experiments and in the basis where the right-handed Majorana mass is diagonal, the charged lepton mixings are tiny. In addition these models link the up-quark Yukawa matrix to the neutrino Yukawa matrix Y^\nu with the special feature of Y^\nu_{11}-> 0 Using this condition, we find that the required baryon asymmetry of the Universe can be explained by the soft leptogenesis using the soft B parameter of the second lightest right-handed neutrino whose mass turns out to be around 10^8 GeV. It is pointed out that a natural way to do so is to use no-scale supergravity where the value of B ~1 GeV is set through gauge-loop corrections.

Soft leptogenesis in the inverse seesaw model

We consider leptogenesis induced by soft supersymmetry breaking terms ("soft leptogenesis"), in the context of the inverse seesaw mechanism. In this model there are lepton number (L) conserving and L-violating soft supersymmetry-breaking B-terms involving the singlet sneutrinos which, together with the -- generically small-- L-violating parameter responsible of the neutrino mass, give a small mass splitting between the four singlet sneutrino states of a single generation. In combination with the trilinear soft supersymmetry breaking terms they also provide new CP violating phases needed to generate a lepton asymmetry in the singlet sneutrino decays. We obtain that in this scenario the lepton asymmetry is proportional to the L-conserving soft supersymmetry-breaking B-term, and it is not suppressed by the L-violating parameters. Consequently we find that, as in the standard see-saw case, this mechanism can lead to sucessful leptogenesis only for relatively small value of the relevant soft bilinear coupling. The right-handed neutrino masses can be sufficiently low to elude the gravitino problem. Also the corresponding Yukawa couplings involving the lightest of the right-handed neutrinos are constrained to be \sum |Y_{1k}|^2\lesssim 10^{-7} which generically implies that the neutrino mass spectrum has to be strongly hierarchical.

Soft leptogenesis in warped extra dimensions

We implement soft leptogenesis in a warped five dimensional scenario with two branes on the orbifold boundaries coming from an S^{1}/Z_{2} symmetry, and supersymmetry broken on the IR brane. The SM hypermultiplet fields (fermions and Higgs) live in the UV brane and we allow the vector supermultiplets corresponding to the gauge bosons and a hypermultiplet corresponding to the right handed neutrino to live in the bulk. We assume that there are Majorana mass terms for the right handed neutrino superfield fixed on each brane and that there is a Yukawa term involving the right handed neutrino, the left handed neutrino and the Higgs fixed on the UV brane. Supersymmetry is broken by a constant ``superpotential'' on the IR brane, which induces an F-term for the radion hypermultiplet. This F-term leads to a B-term for the right handed sneutrinos as well as a soft SUSY breaking gaugino mass in the 4D theory for the zero modes. The gaugino mass naturally induces an A-term for the right handed sneutrino, left handed sneutrino and the Higgs to be formed through gaugino mediation with a non-trivial CP violating phase. Moreover, we show that within the context of extra dimensions, the condition of out-of-equilibrium decay and the phenomenological constraints on the neutrino mass are both satisfied in a natural way, for UV Majorana masses of the order of the fundamental scale of the theory. Thus all necessary elements for soft leptogenesis are at hand and we are able to predict a correct value for the baryon asymmetry.

Soft leptogenesis in Higgs triplet model

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 lepton asymmetry. As a consequence of this, successful leptogenesis can occur only for a triplet mass at the TeV scale, where the contribution of soft supersymmetry breaking terms enhances the CP and lepton asymmetry. This opens up an interesting opportunity for testing the model in future colliders.

TeV leptogenesis in supersymmetricZ-prime models and its collider probe

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.

Natural soft leptogenesis

Successful soft leptogenesis requires small B-terms for the right-handed sneutrinos and a large CP violating phase between the A- and B-terms. We show that this situation is realized naturally within the framework of gauge mediated supersymmetry breaking. The A-term is dominated by contribution from gauge mediation, while supergravity effects are more important for the B-term. The different origins naturally explain simultaneously the smallness of the B-term and the large CP violating phase. The most stringent bounds on the model come from the cosmological gravitino problem. We find a viable parameter region with very light gravitino $m_{3/2} \lesssim 16 eV$, providing a consistent framework for supersymmetry phenomenology, soft leptogenesis and cosmology.