arXiv subjects

Kimmo Kainulainen

Publications and source records attributed to Kimmo Kainulainen.

83 records · Page 5Linked to original sources

arXiv1998

Dynamics of Two Higgs Doublet CP Violation and Baryogenesis at the Electroweak Phase Transition

We quantitatively study the charge transport mechanism of electroweak baryogenesis in a realistic two-Higgs-doublet model, comparing the contributions from quarks and leptons reflecting from electroweak domain walls, and comparing the exact profile of the CP-violating phase with a commonly used ansatz. We note that the phenomenon of spontaneous CP violation at high temperature can occur in this model, even when there is no CP violation at zero temperature. We include all known effects which are likely to influence the baryon production rate, including strong sphalerons, the nontrivial dispersion relations of the quasiparticles in the plasma, and Debye screening of gauged charges. We confirm the claim of Joyce, Prokopec and Turok that the reflection of tau leptons from the wall gives the dominant effect. We conclude that this mechanism is marginally strong enough to produce the observed baryon asymmetry of the universe.

hep-ph↗

arXiv1997

Supersymmetric Electroweak Phase Transition: Dimensional Reduction versus Effective Potential

We compare two methods of analyzing the finite-temperature electroweak phase transition in the minimal supersymmetric standard model: the traditional effective potential (EP) approach, and the more recently advocated procedure of dimensional reduction (DR). The latter tries to avoid the infrared instabilities of the former by matching the full theory to an effective theory that has been studied on the lattice. We point out a limitation of DR that caused a large apparent disagreement with the effective potential results in our previous work. We also incorporate wave function renormalization into the EP, which is shown to decrease the strength of the phase transition. In the regions of parameter space where both methods are expected to be valid, they give similar results, except that the EP is significantly more restrictive than DR for the range of baryogenesis-allowed values of $\tanβ$, $m_h$, the critical temperature, and the up-squark mass parameter $m_U$. In contrast, the DR results are consistent with $2\lsim\tanβ\lsim 4$, $m_h<80$ GeV, and $m_U$ sufficiently large to have universality of the squark soft-breaking masses at the GUT scale, in a small region of parameter space. We suggest that the differences between DR and EP are due to higher-order perturbative corrections rather than infrared effects.

hep-ph↗

arXiv1996

Supersymmetric Electroweak Phase Transition: Beyond Perturbation Theory

We compute the three-dimensional effective action for the minimal supersymmetric standard model, which describes the light modes of the theory near the finite-temperature electroweak phase transition, keeping the one-loop corrections from the third generation quarks and squarks. Using the lattice results of Kajantie {\it et al.}\ for the phase transition in the same class of 3-D models, we find that the strength of the phase transition is sufficient for electroweak baryogenesis, in much broader regions of parameter space than have been indicated by purely perturbative analyses. In particular we find that, while small values of $\tanβ$ are favored, positive results persist even for arbitrarily large values of $\tanβ$ if the mass of the $A^0$ boson is between 40 and 120 GeV, a region of parameters which has not been previously identified as being favorable for electroweak baryogenesis.

hep-ph↗

arXiv1996

Precise Nucleosynthesis Limits on Neutrino Masses

A computation of nucleosynthesis bounds on the masses of long-lived Dirac and Majorana neutrinos is reviewed. In particular an explicit treatment of the ``differential heating'' of the $\nue$ and $\bnue$ ensembles due to the residual out-of-equilibrium annihilations of decoupled heavy neutrinos is included. The effect is found to be considerably weaker than recently reported by Dolgov et al. For example, the bounds for a Dirac tau neutrino are $\mnt < 0.37$ MeV or $\mnt > 25$ MeV (for $\dNu > 1$), whereas the present laboratory bound is $\mnt < 23.1$ MeV.

hep-ph↗

arXiv1996

Model Independent Predictions of Big Bang Nucleosynthesis from \he4 and \li7: Consistency and Implications

We examine in detail how BBN theory is constrained, and what predictions it can make, when using only the most model-independent observational constraints. We avoid the uncertainties and model-dependencies that necessarily arise when solar neighborhood D and \he3 abundances are used to infer primordial D and \he3 via chemical and stellar evolution models. Instead, we use \he4 and \li7, thoroughly examining the effects of possible systematic errors in each. Via a likelihood analysis, we find near perfect agreement between BBN theory and the most model-independent data. Given this agreement, we then {\it assume} the correctness of BBN to set limits on the single parameter of standard BBN, the baryon-to-photon ratio, and to predict the primordial D and \he3 abundances. We also repeat our analysis including recent measurements of D/H from quasar absorption systems and find that the near perfect agreement between theory and observation of the three isotopes, D, \he4 and \li7 is maintained. These results have strong implications for the chemical and stellar evolution of the light elements, in particular for \he3. In addition, our results (especially if the D/H measurements are confirmed) have implications for the stellar depletion of \li7. Finally, we set limits on the number \nnu\ of neutrino flavors, using an analysis which carefully and systematically includes all available experimental constraints. The value \nnu = 3.0 fits best with BBN and a 95\% CL upper limit of \nnu $\la 4$ is established.

astro-ph↗

arXiv1995

Nucleosynthesis Limits on the Mass of Long Lived Tau and Muon Neutrinos

We compute the nucleosynthesis bounds on the masses of stable Dirac and Majorana neutrinos by solving an evolution equation network comprising of all neutrino species which in the Dirac case includes different helicity states as separate species. We will not commit ourselves to any particular value of the nucleosynthesis bound on effective number of light neutrino degrees of freedom $N_ν$, but present all our mass bounds as {\em functions} of $\dNu$. For example, we find that the excluded region in the mass of a Majorana $μ$- or $τ$- neutrino, $0.31$ MeV $< m_ν^M < 52$ MeV corresponding to a bound $\dNu < 0.3$ gets relaxed to $0.93$ MeV $< m_ν^M < 31$ MeV if $\dNu < 1.0$ is used instead. For the Dirac neutrinos this latter constraint gives the upper limits (for $T_{\rm QCD} = 100$ MeV): $\mnm < 0.31$ MeV and $\mnt < 0.37$ MeV. Also, the constraint $\dNu <1$ {\it allows} a stable Dirac neutrino with $m^D_{ν_τ} > 22$ MeV.

hep-ph↗

arXiv1995

Diffusion and Debye Screening Near Expanding Domain Walls

We study the effect of Debye screening of hypercharge when a net fermion number is reflected from a domain wall during a first order phase transition, which may be relevant for electroweak baryogenesis. We give a simple method for computing the effect of screening within the diffusion approximation, whose results are compatible with those of a more elaborate treatment based on the Boltzmann equation. Our formalism takes into account the differences in mobility of different particle species. We believe it is conceptually simpler than other accounts of screening that have appeared in this context. Somewhat surprisingly, we find that Debye screening can actually {\it enhance} electroweak baryogenesis by a modest factor ($\sim 2$).

hep-ph↗

arXiv1995

Primordial Baryon Asymmetry and Sphalerons

I show that a cosmological baryon asymmetry generated at the GUT scale is in general safe against washout due to sphalerons and generic $B$- or $L$-violating effects. This result is mainly due to the (almost) conserved number of right-handed electrons at high temperatures $T \gsim {\cal O}(10) $ TeV, but also the mass corrections, in particular the thermal masses of leptons act as the protector of the primordial baryon asymmetry.

hep-ph↗

arXiv1994

Protecting the Primordial Baryon Asymmetry From Erasure by Sphalerons

If the baryon asymmetry of the universe was created at the GUT scale, sphalerons together with exotic sources of $(B-L)$-violation could have erased it, unless the latter satisfy stringent bounds. We elaborate on how the small Yukawa coupling of the electron drastically weakens previous estimates of these bounds.

hep-ph↗

arXiv1993

Stability of Neutrinos in the Singlet Majoron Model

We show that there is no one-loop enhancement of the rate for a light neutrino to decay into a lighter neutrino plus a majoron, contrary to a recent claim. Thus the light neutrinos must satisfy the cosmological bound of having masses less than 35 eV in the singlet majoron model, or else violate the constraint imposed by galaxy formation. In the latter case, $ν_τ$ could have a mass between 40 and 500 keV, while satisfying all other cosmological constraints.

hep-ph↗

arXiv1993

Constraints on Majoron Models, Neutrino Masses and Baryogenesis

We derive strong contraints on the Yukawa couplings and the vacuum expectation value in the singlet majoron model, taking into account the possibility of a small gravitationally induced mass for the majoron. If the present baryon asymmetry was created earlier than at the electroweak phase transition, then to preserve it from the combined effects of lepton number violating interactions and electroweak sphalerons, we find that stringent constraints on the Yukawa couplings, $h < 10^{-7}$, and the majoron scale, $v_s < v_{EW}$, must be satisfied. We also carefully rederive baryogenesis bounds on neutrino masses, finding that in general they apply not to the masses themselves, but only to related parameters, and they are numerically somewhat less stringent than has previously been claimed.

hep-ph↗