Leptogenesis at the electroweak scale

In this Letter we propose a model of leptogenesis in which the scale for the mass of the necessary heavy neutral lepton is similar to the scale of electroweak symmetry breaking.     

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 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.     

Magnetic field production during preheating at the electroweak scale

We study the generation of magnetic fields during preheating within a scenario of hybrid inflation at the electroweak scale. We find that the nonperturbative and strongly out-of-equilibrium process of generation of magnetic fields with a nontrivial helicity occurs along the lines predicted by Vachaspati many years ago. The magnitude (rho_{B}/rho_{EW} approximately 10{-2}) and correlation length of these helical magnetic fields grow linearly with time during preheating and are consistent with the possibility that these seeds gave rise to the microgauss fields observed today in galaxies and clusters of galaxies.     

Baryogenesis at the MeV era

The addition of a single operator to the minimal low-energy supergravity theory allows baryogenesis to occur at the end of inflation. The reheat temperature is between an MeV and GeV and there is no gravitino problem. The model can be tested by searching for baryon number violation in e⁺e^- collisions.     

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.     

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.     

Baryogenesis and neutron-antineutron oscillation at TeV

We propose a TeV extension of the standard model to generate the cosmological baryon asymmetry with an observable neutron-antineutron oscillation. The new fields include a singlet fermion, an isotriplet and two isosinglet diquark scalars. There will be no proton decay although the Majorana mass of the singlet fermion as well as the trilinear couplings between one isosinglet diquark and two isotriplet diquarks softly break the baryon number of two units. The isosinglet diquarks couple to two right-handed down-type quarks or to a right-handed up-type quark and a singlet fermion, whereas the isotriplet diquark couples to two left-handed quarks. The isosinglet diquarks mediate the three-body decays of the singlet fermion to realize a TeV baryogenesis without fine tuning the resonant effect. By the exchange of one singlet fermion and two isosinglet diquarks and of one isosinglet diquark and two isotriplet diquarks, a neutron-antineutron oscillation is allowed to verify in the future experiments.     

Baryogenesis

Developments in understanding of baryogenesis are reviewed. We start with early motivations and the proposals in the context of GUTs. Next, the importance of the sphaleron solution and its implications are discussed. Studies of the Standard Model reveal that the latter has a Higgs structure incompatible with existence of observed B asymmetry. We then discuss a generic scenario for electroweak baryogenesis relying on bubble wall dynamics. We also summarise the status of the MSSM, and alternative scenarios utilising topological defects as the source of non-equilibrium behaviour and leptogenesis     

Seesaw induced electroweak scale, the hierarchy problemand sub-eV neutrino masses

We describe a model for the scalar sector where all interactions occur either at an ultra-high scale, Λ_U~10¹⁶-10¹⁹ GeV, or at an intermediate scale, Λ_I = 10⁹-10¹¹ GeV. The interaction of physics on these two scales results in an SU(2) Higgs condensate at the electroweak (EW) scale, Λ_EW, through a seesaw-like Higgs mechanism, , while the breaking of the SM SU(2) x U(1) gauge symmetry occurs at the intermediate scale Λ_I . The EW scale is, therefore, not fundamental but is naturally generated in terms of ultra-high energy phenomena and so the hierarchy problem is alleviated. We show that the class of such "seesaw Higgs" models predict the existence of sub-eV neutrino masses which are generated through a "two-step" seesaw mechanism in terms of the same two ultra-high scales: . The neutrinos can be either Dirac or Majorana, depending on the structure of the scalar potential. We also show that our seesaw Higgs model can be naturally embedded in theories with tiny extra dimensions of size fm, where the seesaw induced EW scale arises from a violation of a symmetry at a distant brane; in particular, in the scenario presented there are seven tiny extra dimensions. Received: 19 August 2004, Revised: 27 July 2005, Published online: 14 October 2005     

Bloch-nordsieck violating electroweak corrections to inclusive TeV scale hard processes

We point out that, since the colliders' initial states ( e(+)e(-),pp, p&pmacr;,ellipsis) carry a definite non-Abelian flavor, electroweak radiative corrections to inclusive hard cross sections at the TeV scale are affected by peculiar Bloch-Nordsieck violating double logs. We recall the setup of soft cancellation theorems, and we analyze the magnitude of the noncanceling terms in the example of electron-positron annihilation into hadrons.     

Determination of the electroweak chiral-lagrangian parameters at the LHC

In this work we report on the results obtained in a detailed and systematical study of the possibility to measure the parameters appearing in the electroweak chiral lagrangian. The main novelty of our approach is that we do not use the equivalence theorem and therefore we work explicitly with all the gauge boson degrees of freedom.