Topological Dark Matter from the Theory of Composite Electroweak Symmetry Breaking

The lightest electroweak baryon as a topological object is investigated by using a general effective Lagrangian of composite electroweak symmetry breaking and the spin-independent electroweak baryon-nucleon scattering cross section is calculated. We explicitly show the masses of the electroweak baryons and the cross section as functions of the Peskin-Takeuchi S parameter and the ratio of the masses of axial-vector and vector composite bosons. We find that it is acceptable to regard the electroweak baryon as a dark matter candidate and the even number of technicolor is favored.     

Indications on the mass of the lightest electroweak baryon

In general, an effective low-energy Lagrangian model of composite electroweak symmetry breaking contains soliton solutions that may be identified with technibaryons. We recall how the masses of such states may be related to the coefficients of fourth-order terms in the effective Lagrangian, and review the qualitative success of this approach for baryons in QCD. We then show how the current theoretical and phenomenological constraints on the corresponding fourth-order coefficients in the electroweak theory could be used to estimate qualitative lower and upper bounds on the lightest electroweak baryon mass. We also discuss how the sensitivity of the LHC experiments could enable these bounds to be improved.     

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.     

Monte Carlo simulation of baryon and lepton number violating processes at high energies

We report results obtained with the first complete event generator for electroweak baryon and lepton number violating interactions at supercolliders. Typical events contain of the order of 50 electroweak gauge bosons, some Higgs bosons and quarks and leptons of all generations. There is still great uncertainty about the expected rate, but an event generator is needed in any case to establish what experimental limits can be placed on the cross section, and to determine whether, even if such spectacular events are seen, baryon and/or lepton number violation can be conclusively demonstrated. We find that baryon number violation would be very difficult to establish, but lepton number violation can be seen provided at least a few hundredL violating events are available with good electron or muon identification in the energy range 10 GeV to 1 TeV. The event generator, which takes the form of a package (HERBVI) interfacing to the existing simulation program HERWIG, should be useful for the coming period of detailed experiment design for the Large Hadron Collider (LHC) at CERN.     

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.     

The νMSM,inflation, and dark matter

We show how to enlarge the νMSM (the minimal extension of the Standard Model by three right-handed neutrinos) to incorporate inflation and provide a common source for electroweak symmetry breaking and for right-handed neutrino masses. In addition to inflation, the resulting theory can explain simultaneously dark matter and the baryon asymmetry of the Universe; it is consistent with experiments on neutrino oscillations and with all astrophysical and cosmological constraints on sterile neutrino as a dark matter candidate. The mass of inflaton can be much smaller than the electroweak scale.     

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.

     

Baryogenesis from the Kobayashi-Maskawa phase

The smallness of quark masses suppresses the CP violation from the Kobayashi-Maskawa phase to a level that is many orders of magnitude below what is required to explain the observed baryon asymmetry. We point out that if, as a result of time variation in the Yukawa couplings, quark masses were large at the time of the electroweak phase transition, then the Kobayashi-Maskawa mechanism could be the source of the asymmetry. The Froggatt-Nielsen mechanism provides a plausible framework where the Yukawa couplings could all be of order 1 at that time, and settle to their present values before nucleo-synthesis. The problems related to a strong first order electroweak phase transition may also be alleviated in this framework. Our scenario reveals a loophole in the commonly held view that the Kobayashi-Maskawa mechanism cannot be the dominant source of CP violation to play a role in baryogenesis.     

Neutrino masses in supersymmetry: R-parity and leptogenesis

In the supersymmetric standard model of particle interactions, R-parity nonconservation is often invoked to obtain nonzero neutrino masses. We point out here that such interactions of the supersymmetric particles would erase any pre-existing lepton or baryon asymmetry of the universe before the electroweak phase transition through the B+L violating sphaleron processes. We also point out that all models of radiative generation of neutrino masses suffer from the same problem. We then show how neutrino masses may be obtained in supersymmetry (assuming R-parity conservation) together with successful leptogenesis and predict the possible existence of new observable particles.     

Associate Higgs and gauge boson production at hadron colliders in a model with vector resonances

Motivated by new models of dynamical electroweak symmetry breaking that predict a light composite Higgs boson, we build an effective Lagrangian which describes the standard model (with a light Higgs) and vector resonances. We compute the cross section for the associate production of a Higgs and a gauge boson. For some values of model parameters we find that the cross section is significantly enhanced with respect to the standard model. This enhancement is similar at the LHC (large hadron collider) and the Tevatron for the same range of resonance mass. PACS 12.60.Nz     

Leptogenesis from spin-gravity coupling following inflation

The energy levels of the left- and the right-handed neutrinos are split in the background of gravitational waves generated during inflation, which, in presence of lepton-number-violating interactions, gives rise to a net lepton asymmetry at equilibrium. Lepton number violation is achieved by the same dimension five operator which gives rise to neutrino masses after electroweak symmetry breaking. A net baryon asymmetry of the same magnitude can be generated from this lepton asymmetry by electroweak sphaleron processes.     

Postsphaleron baryogenesis

We present a new mechanism for generating the baryon asymmetry of the Universe directly in the decay of a singlet scalar field S(r) with a weak scale mass and a high dimensional baryon number-violating coupling. Unlike most currently popular models, this mechanism, which becomes effective after the electroweak phase transition, does not rely on the sphalerons for inducing a nonzero baryon number. CP asymmetry in S(r) decay arises through loop diagrams involving the exchange of W+/- gauge bosons and is suppressed by light quark masses, leading naturally to a value of eta(B) approximately 10(-10). The simplest realization of this idea which uses a six quark DeltaB=2 operator predicts colored scalars accessible to the CERN Large Hadron Collider and neutron-antineutron oscillation within reach of the next-generation experiments.     

Baryogenesis via density fluctuations with a second-order electroweak phase transition

We consider the presence of cosmic string-induced density fluctuations in the early universe at temperatures below the electroweak phase transition temperature. Resulting temperature fluctuations can restore the electroweak symmetry locally, depending on the amplitude of fluctuations and the background temperature. The symmetry will be spontaneously broken again in a given region as the temperature drops there (for fluctuations with length scales smaller than the horizon), resulting in the production of baryon asymmetry. The time-scale of the transition will be governed by the wavelength of fluctuation and, hence, can be much smaller than the Hubble time. This leads to strong enhancement in the production of baryon asymmetry for a second-order electroweak phase transition as compared to the case when transition happens due to the cooling of the universe via expansion. For a two-Higgs doublet model (with appropriate CP violation), we show that one can get the required baryon asymmetry if fluctuations propagate without getting significantly damped. If fluctuations are damped rapidly, then a volume factor suppresses the baryon production, though it is still 3–4 orders of magnitude larger than the conventional case of second-order transition.     

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.     

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.     

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.     

Cold electroweak baryogenesis with Standard Model CP violation

We study a mechanism that generates the baryon asymmetry of the Universe during a tachyonic electroweak phase transition. We utilize as sole source of CP violation an operator that was recently obtained from the Standard Model by integrating out the quarks.     

Leptogenesis from neutralino decay with nonholomorphic R-parity violation

In supersymmetric models with lepton-number violation, hence also R-parity violation, it is easy to have realistic neutrino masses, but then leptogenesis becomes difficult to achieve. After explaining the general problems involved, we study the details of a model which escapes these constraints and generates a lepton asymmetry, which gets converted into the present observed baryon asymmetry of the Universe through the electroweak sphalerons. This model requires the presence of certain nonholomorphic R-parity violating terms. For completeness we also present the most general R-parity violating Lagrangian with soft nonholomorphic terms and study their consequences for the charged-scalar mass matrix. New contributions to neutrino masses in this scenario are discussed.     

Electroweak baryon number violation at finite temperature

We consider baryon and lepton number violating processes in the electroweak theory induced by gauge and Higgs fields passing the sphaleron solution at finite temperature. We show that for temperatures larger than 19 GeV the anomalous baryon and lepton number violating processes are suppressed by the Boltzmann factor exp (?βE _sp), whereE _sp is the sphaleron energy, rather than by the instanton tunneling factor exp (?8π²/g ²). We caculate the rate of baryon and lepton number violating processes at finite temperature and determine the freezing temperature of the anomalous processes in the early universe as a function of the Higgs mass. We compare the freezing temperature with the critical temperature of the electroweak phase transition infered from the one-loop finite-temperature effective potential. We obtain a critical Higgs mass of the order of 100 GeV, slightly depending on the top mass and the magnitude of the pre-exponential factor in the rate of theB non-conservation, above which the anomalous processes are certainly in equilibrium after the electroweak phase transition. Assuming that the temperature-dependence of the sphaleron energy is given by that found from the one-loop finitetemperature effective potential, this critical Higgs mass is lowered to a value of the order of 50 GeV.     

Rate of anomalous electroweak baryon and lepton number violation at finite temperature

Using Langer's statistical theory of the decay of metastable states we calculate the rate of the anomalous electroweak baryon and lepton number violating processes in the case that the electroweak phase transition is of second order. Our formulas are valid in a temperature range between M_w and the critical temperature T_c. We get a dissipation of the baryon and lepton number of the order of exp(4.6×10⁹).