Baryogenesis at the weak phase transition

The weak phase transition of the hot big bang can produce quarks, leptons and weak bosons which are out of thermal equilibrium. In a simple extension of the standard model it is shown that the reactions following top quark decays can generate the cosmological baryon asymmetry. The top quark mass must be close to 80 GeV and the Higgs boson must be lighter than 1 GeV. This baryogenesis mechanism can be directly tested at e⁺e⁻ and hadron collider by searching for spectacular events containing six or more bottom quarks and a violation of baryon number at the decay vertex of a long lived neutral particle.     

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.     

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.     

Baryogenesis and damping in nonminimal electroweak models

We calculate the baryon asymmetry of the Universe in the standard model of the electroweak theory with CP violation appropriate for simple extensions of the Higgs sector. The propagation of quarks of masses up to about 5 GeV are considered, taking into account the effect of damping rate. We find that the contribution of the b quark can still account for the observed baryon asymmetry to within the theoretical uncertainties of such models.

     

Baryon asymmetry,stable proton and n-n̄ oscillations in superstring models

The violation of baryon number is discussed in the context of a gauge model inspired by the E₈ × E₈ superstring theory. Lepton number is an accidental unbroken symmetry of the model. The proton, as a consequence, is essentially stable. The model yields an acceptable value (∼10⁻¹⁰) for the baryon asymmetry in the universe. It also predicts n-n̄ oscillations at a rate which may be amenable to ongoing experimental searches.     

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.     

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.     

Electroweak baryogenesis

After a short general introduction to baryogenesis — the creation of a baryon asymmetry in our universe (BAU) — I will highlight some old and more recent models of electroweak baryogenesis: modifications of the Standard Model (SM), in particular supersymmetric ones as the MSSM, NMSSM, nMSSM, BMSSM, νμMSSM. I will also stress the role of electric dipole moments (EDMs) in limiting the CP violation needed for baryogenesis.     

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.     

The strong CP problem revisited

The strong CP-violating θ parameter, the problem of strong CP violation and their status are reviewed. Among all possibilities, two natural solutions to the strong CP puzzle are thoroughly discussed and emphasized: the axion-type mechanism for hard CP violation and the non-Peccei-Quinn scheme for spontaneous CP nonconservation. Basic properties of the axion are derived from the modified Peccei-Quinn symmetry. Astrophysical and cosmological constraints are described for two different types of invisible axions. In nonaxion solutions, CP is spontaneously broken at the grand-unification scale and the CP phase is transmitted down to the low energy sector by quantum effects or by fermion mixing effects. As a by-product, the cosmological baryon asymmetry, which is caused by the same source of CP violation ultimately responsible for the kaon ε parameter, is generated adequately at the one-loop level.     

Feynman scaling violation on baryon spectra in pp collisions at LHC and cosmic ray energies

A significant asymmetry in baryon/antibaryon yields in the central region of high energy collisions is observed when the initial state has nonzero baryon charge. This asymmetry is connected with the possibility of baryon charge diffusion in rapidity space. Such a diffusion should decrease the baryon charge in the fragmentation region and translate into the corresponding decrease of the multiplicity of leading baryons. As a result, a new mechanism for Feynman scaling violation in the fragmentation region is obtained. Another numerically more significant reason for the Feynman scaling violation comes from the fact that the average number of cut Pomerons increases with initial energy. We present the quantitative predictions of the Quark-Gluon String Model for the Feynman scaling violation at LHC energies and at even higher energies that can be important for cosmic ray physics.     

Structure of the high temperature gauge ground state and electroweak production of the baryon asymmetry

We investigate the connection of the baryon asymmetry of the universe (BAU) with the Chern-Simons structure of the ground state of gauge theories at high temperatures. We formulate in an explicitly gauge-invariant way the notion of the effective potential for density of the Chern-Simons charge and estimate CP noninvariant corrections to it coming from the nonequilibrium stages of universe expansion. We find that for the case of trivial structure of the ground state the BAU production is only possible if the low-energy CP violation in anomalous reactions δ_ms is larger than 10⁻⁴. We discuss the fate of the CP domain structure of the universe which appears when there is discrete degeneracy of the ground state. The magnitude of BAU could be large only with sufficiently strong high temperature CP violation. So the BAU generation in the framework of standard electroweak theory (where δ_ms∼10⁻¹⁸) takes place only when there is infinite degeneracy. We estimate the Higgs and top masses in the Coleman-Weinberg type of theory.     

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.     

Leptogenesis with left-right domain walls

The presence of domain walls separating regions of unbrokenSU(2)_L andSU(2)_R is shown to provide necessary conditions for leptogenesis which converts later to the observed baryon asymmetry. The strength of lepton number violation is related to the Majorana neutrino mass and hence related to current bounds on light neutrino masses. Thus the observed neutrino masses and the baryon asymmetry can be used to constrain the scale of left-right symmetry breaking.     

Baryon production in lepton-nucleon scattering and diquark fragmentation

We study baryon production in deep inelastic scattering using an extended version of the Lund jet model. There are two contributing sources. The first is baryon production in the target fragmentation. In a scheme related to our earlier work on lowp _hu baryon fragmentation we present some details of the fragmentation of a diquark into baryons and mesons. A non-negligible baryon-antibaryon production is observed ine ⁺ e ^? annihilation. In a previous paper we developed a model for this production, and the same mechanism should also give fast baryons in leptoproduction. In this paper we discuss those features of baryon production which can be more easily studied in a leptoproduction experiment.     

Scaling in e+e− annihilation into hadrons

The possibility is discussed that the violation of scaling observed in e⁺e^? annihilation is due to the opening of the baryon pair channels. One particle distributions are assumed to scale apart from final state interactions. The threshold effects are computed.     

Explicit R-parity breaking in supersymmetric models

Supersymmetric models generally invoke R parity to ensure that baryon and lepton numbers are symmetries of the renormalizable operators of the low-energy effective theory. The phenomenology of lepton-number violation is analyzed in low-energy models in which R parity is explicitly broken by superrenormalizable operators. Constraints on lepton-number violating parameters are found to be mild. The photino is able to decay, avoiding a stringent cosmological lower bound on its mass. Alternatives to R parity are considered in the context of an SU(5) grand unified model coupled to N=1 supergravity. One possibility, θ parity, leads to new mechanisms for baryon- number violation in addition to lepton-number violation.     

Phenomenology of the standard model under conditions of spontaneously broken mirror symmetry

Spontaneously broken mirror symmetry is able to reproduce observed qualitative properties of weak mixing for quark and leptons. Under conditions of broken mirror symmetry, the phenomenology of leptons—that is, small neutrino masses and a mixing character other than that in the case of quarks—requires the Dirac character of the neutrinos and the existence of processes violating the total lepton number. Such processes involve heavy mirror neutrinos; that is, they proceed at very high energies. Here, CP violation implies that a P-even mirror-symmetric Lagrangian must simultaneously be T-odd and, according to the CPT theorem, C-odd. All these properties create preconditions for the occurrence of leptogenesis, which is a mechanism of the emergence of the baryon–lepton asymmetry of the universe in models featuring broken mirror symmetry.     

Realistic neutrinogenesis with radiative vertex correction

We propose a new model for naturally realizing light Dirac neutrinos and explaining the baryon asymmetry of the universe through neutrinogenesis. To achieve these, we present a minimal construction which extends the Standard Model with a real singlet scalar, a heavy singlet Dirac fermion and a heavy doublet scalar besides three right-handed neutrinos, respecting lepton number conservation and a Z₂$Z_2$ symmetry. The neutrinos acquire small Dirac masses due to the suppression of weak scale over a heavy mass scale. As a key feature of our construction, once the heavy Dirac fermion and doublet scalar go out of equilibrium, their decays induce the CP asymmetry from the interference of tree-level processes with the radiative vertex corrections (rather than the self-energy corrections). Although there is no lepton number violation, an equal and opposite amount of CP asymmetry is generated in the left-handed and the right-handed neutrinos. The left-handed lepton asymmetry would then be converted to the baryon asymmetry in the presence of the sphalerons, while the right-handed lepton asymmetry remains unaffected.