Spontaneous baryogenesis

The recently discovered mechanism of “spontaneous baryogenesis” for generating the baryon asymmetry is implemented in several particle physics models. In these scenarios, baryon number is an approximate symmetry spontaneously broken at a scale |;. The baryon asymmetry is generated without CP violation. Furthermore, this can come about during an epoch when baryon violation is in thermal equilibrium. We consider how various observational constraints affect the realization of this mechanism in acceptable models of particle interactions, and find that the observed baryon asymmetry can be produced for |;≳ 3 × 10¹³ GeV.     

Baryon asymmetry, inflation and squeezed states

We use the general formalism of squeezed rotated states to calculate baryon asymmetry in the wake of inflation through parametric amplification. We base our analysis on a B and CP violating Lagrangian in an isotropically expanding universe. The B and CP violating terms originate from the coupling of complex fields with non-zero baryon number to a complex background inflaton field. We show that a differential amplification of particle and antiparticle modes gives rise to baryon asymmetry.     

Leptogenesis and composite heavy neutrinos with gauge-mediated interactions

Leptogenesis is an appealing framework to account for the baryon asymmetry in the universe. To this end physics beyond the standard model is demanded. In this paper we investigate the possibility to attain successful leptogenesis with composite Majorana neutrinos. We work in the framework of effective gauge-mediated and contact interactions without any reference to an underlying compositeness theory. This approach is the one adopted in all current experimental searches for composite fermions at colliders. In the case of gauge-mediated interactions, we calculate the CP asymmetry in heavy composite neutrino decays. Both the direct and the indirect CP asymmetry are derived and resonant leptogenesis is also discussed. We find that the Sakharov conditions can be met and, for some choice of the parameters, the correct order of magnitude of the baryon asymmetry is reproduced.     

Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon

There are two mechanisms for the generation of an asymmetry between the strange and anti-strange quark distributions in the nucleon: nonperturbative contributions originating from nucleons fluctuating into virtual baryon?Cmeson pairs such as ??K and ??K, and perturbative contributions arising from gluons splitting into strange and anti-strange quark pairs. While the nonperturbative contributions are dominant in the large-x region, the perturbative contributions are more significant in the small-x region. We calculate this asymmetry taking into account both nonperturbative and perturbative contributions, thus giving a more accurate evaluation of this asymmetry over the whole domain of x. We find that the perturbative contributions are generally a few times larger in magnitude than the nonperturbative contributions, which suggests that the best region to detect this asymmetry experimentally is in the region 0.02<x<0.03. We find that the asymmetry may have more than one node, which is an effect that should be taken into account, e.g. for parameterizations of the strange and anti-strange quark distributions used in global analysis of parton distributions.     

Baryogenesis and lepton number violation

The cosmological baryon asymmetry can be explained by the nonperturbative electroweak reprocessing of a lepton asymmetry generated in the out-of-equilibrium decay of heavy right-handed Majorana neutrinos. We analyze this mechanism in detail in the framework of a SO(10)-subgroup. We take three right-handed neutrinos into account and discuss physical neutrino mass matrices.     

Baryon asymmetry of the proton sea at low-x

We predict a nonvanishing baryon asymmetry of the proton sea at low x. It is expected to be about 7% and nearly x-independent at x < 0.5 × 10^-3. The asymmetry arises from the baryon-antibaryon component of the Pomeron, rather than from the valence quarks of the proton, which are wide believed carriers of baryon number. Experimental study of x-distribution of the baryon asymmetry of the proton sea can be performed in ep or γp interactions at HERA, where x ～ 10^-5 are reachable, smaller than at any of existing or planned proton colliders.     

Thermodynamic generation of the baryon asymmetry

A new technique for generating the baryon asymmetry of the universe is discussed. By using the natural CPT non-invariance of the universe during its early history, we discuss how a baryon asymmetry can develop while baryon violating interactions are still in thermal equilibrium with respect to an effective hamiltonian. Furthermore, both the ground state and fundamental interactions in these theories can be CP conserving.     

Baryogenesis in the chaotic inflationary cosmology

Baryogenesis in the reheating phase of the chaotic inflationary universe is investigated, taking into account the non-thermal production of baryon-number non-conserving Higgs bosons from an inflation field. It is found that the baryon asymmetry may have different signs depending on the reheat temperature. Furthermore a model is presented in which appear universes with various baryon/entropy ratio and also antimatter universes as well as our universe, even though CP violation has a definite sign.     

Baryon number generation from cosmic string loops

Baryon number generation due to the decay of particle-antiparticle pairs created from cosmic string loops is studied. In the situation when cusp evaporation occurs a significant baryon asymmetry (baryon/entropy ∼ 10⁻⁴ ϵ: ϵ is a net baryon asymmetry generated from one pair of particle-antiparticle) can be generated.     

Baryogenesis at the electroweak scale

The generation of the baryon asymmetry of the universe is considered in the standard model of the electroweak theory with simple extensions of the Higgs sector. The propagation of quarks of masses up to about 5 GeV are considered, taking into account their markedly different dispersion relations due to propagation through the hot electroweak plasma. It is shown that the contribution of the b quark to the baryon asymmetry can be comparable to that for the t quark considered earlier.     

Leptogenesis and dark matter unified in a non-SUSY model for neutrino masses

We propose a unified explanation for the origin of dark matter and baryon number asymmetry on the basis of a non-supersymmetric model for the neutrino masses. Neutrino masses are generated in two distinct ways, that is, a tree-level seesaw mechanism with a single right-handed neutrino, and one-loop radiative effects by a new additional doublet scalar. A spontaneously broken U(1)^′ brings about a Z₂ symmetry which restricts couplings of this new scalar and controls the neutrino masses. It also guarantees the stability of a CDM candidate. We examine two possible candidates for the CDM. We also show that the decay of a heavy right-handed neutrino related to the seesaw mechanism can generate baryon number asymmetry through leptogenesis.     

Baryogenesis at low reheating temperatures

We note that the maximum temperature during reheating can be much greater than the reheating temperature T(r) at which the universe becomes radiation dominated. We show that the standard model anomalous (B+L)-violating processes can therefore be in thermal equilibrium for 1 GeV less, similarT(r)<100 GeV. Electroweak baryogenesis could work and the traditional upper bound on the Higgs mass coming from the requirement of the preservation of the baryon asymmetry may be relaxed. Alternatively, the baryon asymmetry may be reprocessed by sphaleron transitions either from a (B-L) asymmetry generated by the Affleck-Dine mechanism or from a chiral asymmetry between e(R) and e(L) in a B-L = 0 universe.     

Singlino-driven electroweak baryogenesis in the next-to-MSSM

We explore a new possibility of electroweak baryogenesis in the next-to-minimal supersymmetric standard model. In this model, a strong first-order electroweak phase transition can be achieved due to the additional singlet Higgs field. The new impact of its superpartner (singlino) on the baryon asymmetry is investigated by employing the closed-time-path formalism. We find that the CP violating source term fueled by the singlino could be large enough to generate the observed baryon asymmetry of the Universe without any conflicts with the current constraints from the non-observation of the thallium, neutron and mercury electric dipole moments.     

Baryon asymmetry from a two stage electroweak phase transition?

We investigate an extension of the Standard Model with a second Higgs doublet, showing a two stage phase transition. Wash-out of a baryon asymmetry after the phase transition can be easily avoided in this class of models.B+L transitions are more strongly suppressed in the intermediate phase than in the high temperature symmetric phase, however. Therefore, it becomes more difficult if not impossible to generate a sufficient baryon asymmetry during the phase transition.supported by Landes Graduierten Förderungs Gesetz     

Dirac neutrinos in superstring models with an intermediate scale

We discuss neutrino masses in superstring-inspired models. We present a model possessing an intermediate scale ∼ 10⁸–10⁹ GeV which gives rise to Dirac neutrinos with masses in a range that can account both for the dark matter and the solar neutrino puzzle through the MSW effect. It also accounts for the observed baryon asymmetry through the out-of-equilibrium decay of heavy colored fields at temperatures close to the electroweak scale. Although baryon- and lepton-number symmetries are explicitly broken there are no observable low-energy baryon- or lepton-number-violating effects due to the presence of an accidental unbroken global U(1)_2B−L symmetry.     

Models of neutrino masses and baryogenesis

Majorana masses of the neutrino implies lepton number violation and is intimately related to the lepton asymmetry of the universe, which gets related to the baryon asymmetry of the universe in the presence of the sphalerons during the electroweak phase transition. Assuming that the baryon asymmetry of the universe is generated before the electroweak phase transition, it is possible to discriminate different classes of models of neutrino masses. While see-saw mechanism and the triplet Higgs mechanism are preferred, the Zee-type radiative models and the R-parity breaking models requires additional inputs to generate baryon asymmetry of the universe during the electroweak phase transition.     

Asymmetric dark matter from hidden sector baryogenesis

We consider the production of asymmetric dark matter during hidden sector baryogenesis. We consider a particular supersymmetric model where the dark matter candidate has a number density approximately equal to the baryon number density, with a mass of the same scale as the b, c and τ. Both baryon asymmetry and dark matter are created at the same time in this model. We describe collider and direct detection signatures of this model.     

Baryon asymmetry and low energy parity restoration

We examine the question of baryon number generation in the early universe in theories with low intermediate mass scales It is shown that the recently proposed O(10) grand unified theory with parity restoration at E ≈ few hundred GeV allows for the creation of matter-antimatter asymmetry in accord with cosmological observations. This evades a recent general argument for incompatibility between weakly broken left-right symmetry and substantial baryon generation.     

The baryon asymmetry and CPT invariance in the early universe

We discuss, and give a definite, simple phenomenological example, of the possibility that the baryon asymmetry is related to a failure of CPT invariance for a brief time interval at the origin of the universe.     

CPT violation and particle-antiparticle asymmetry in cosmology

General features of generation of the cosmological charge asymmetry in CPT noninvariant world are discussed. If the effects of CPT violationmanifest themselves only inmass differences of particles and antiparticles, the baryon asymmetry of the Universe hardly can be explained solely by breaking of CPT invariance. However, CPT noninvariant theories may lead to a new effect of distorting the usual equilibrium distributions. If this takes place, CPT violation may explain the baryon asymmetry of the Universe.