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Showing papers on "Electroweak interaction published in 1996"


Journal ArticleDOI
TL;DR: In this paper, the CP violation in the decays of heavy electroweak singlet neutrinos arising from both the one-loop vertex corrections and the wave function mixing was investigated.

724 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that there is no hot electroweak phase transition at large Higgs masses, mH = 95, 120 and 180 GeV, and that the line of first order phase transitions separating the symmetric and broken phases at small mH has an end point mH,c.
Abstract: We provide non-perturbative evidence for the fact that there is no hot electroweak phase transition at large Higgs masses, mH = 95, 120 and 180 GeV. This means that the line of first order phase transitions separating the symmetric and broken phases at small mH has an end point mH,c. In the minimal standard electroweak theory 70 GeV < mH,c < 95 GeV and most likely mH,c ≈ 80 GeV. If the electroweak theory is weakly coupled and the Higgs boson is found to be heavier than the critical value (which depends on the theory in question), cosmological remnants from the electroweak epoch are improbable.

572 citations


Journal ArticleDOI
TL;DR: In this paper, the CP violation in the decays of heavy electroweak singlet neutrinos arising from both the one-loop vertex corrections and the wave function mixing was investigated.
Abstract: We compute the CP violation in the decays of heavy electroweak singlet neutrinos, arising from both the one--loop vertex corrections and the wave function mixing. We extend the computation to the supersymmetric version of the model and discuss the implications for the generation of a lepton number asymmetry by the out of equilibrium decay of the heavy (s)neutrinos in the early Universe, to be reprocessed later in the observed baryon excess by anomalous electroweak processes.

547 citations


Journal ArticleDOI
TL;DR: In this paper, the authors generalize the analytical expressions for the two-loop leading-log neutral Higgs boson masses and mixing angles to the case of general left-and right-handed soft supersymmetry breaking stop and sbottom masses and left-right mixing mass parameters.

470 citations


Journal ArticleDOI
TL;DR: In this paper, the anomalous baryon number nonconservation at high temperatures and in high energy collisions is reviewed and applications to electroweak baryogenesis are considered, and the current status of the problem of instanton-like processes at high energies is outlined.
Abstract: We review recent progress in the study of the anomalous baryon number non-conservation at high temperatures and in high energy collisions. Recent results on high temperature phase transitions are described, and applications to electroweak baryogenesis are considered. The current status of the problem of electroweak instanton-like processes at high energies is outlined. This paper is written on the occasion of Sakharov’s 75th anniversary and will appear in the memorial volume of Uspekhi (Usp. Fiz. Nauk, volume 166, No 5, May 1996).

424 citations


Journal ArticleDOI
TL;DR: In this article, the 3D SU(2)+Higgs model is studied on the lattice and the 3-loop correction to the effective potential of the scalar field is determined.

412 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated Higgs pair production in gluon-gluon collisions and analyzed the cross-sections of the neutral Higgs particles in the minimal supersymmetric extension.

382 citations


Journal ArticleDOI
TL;DR: In this paper, an analysis of the electroweak phase transition in the Minimal Supersymmetric Standard Model, in the presence of light stops, has been performed and it has been shown that the order parameter v(Tc)/Tc can become significantly larger than one, for values of the Higgs and supersymmetric particle masses consistent with the present experimental bounds.

310 citations


Journal ArticleDOI
TL;DR: Working within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking, the cosmological relic density from lightest neutralinos produced in the early universe is evaluated.
Abstract: Working within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking, we evaluate the cosmological relic density from lightest neutralinos produced in the early universe. Our numerical calculation is distinct in that it involves direct evaluation of neutralino annihilation cross sections using helicity amplitude techniques, and thus avoids the usual expansion as a power series in terms of neutralino velocity. Thus, our calculation includes relativistic Boltzmann averaging, neutralino annihilation threshold effects, and proper treatment of integration over Breit-Wigner poles. We map out regions of parameter space that give rise to interesting cosmological dark matter relic densities. We compare these regions with recent calculations of the reach for supersymmetry by CERN LEP 2 and Fermilab Tevatron Main Injector era experiments. The cosmologically favored regions overlap considerably with the regions where large trilepton signals are expected to occur at the Tevatron. The CERN LHC pp collider can make a thorough exploration of the cosmologically favored region via gluino and squark searches. In addition, over most of the favored region, sleptons ought to be light enough to be detectable at both LHC and at \ensuremath{\surd}s =500 GeV ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ collider. \textcopyright{} 1996 The American Physical Society.

261 citations


Journal ArticleDOI
TL;DR: In this article, the mixing of right-handed heavy Majorana neutrinos creates a CP-asymmetric universe, and when these Majorana Neutrinos subsequently decay more lepton than anti leptons are produced, the asymmetry is finally converted into baryon asymmetry during the electroweak phase transition.

259 citations


Journal ArticleDOI
TL;DR: In this article, the authors use the Standard Model all the way to the Planck scale, and do not introduce supersymmetry or any extension of the standard model gauge group, which is a special case of what they call the multiple point criticality principle.

Journal ArticleDOI
TL;DR: The baryon density which may be produced during the electroweak phase transition in supersymmetric models is computed, taking into account the previously neglected effects of transport, strong and weak anomalous fermion number violation, thermal scattering, and a new method for computing violating processes during the transition.
Abstract: The baryon density which may be produced during the electroweak phase transition in supersymmetric models is computed, taking into account the previously neglected effects of transport, strong and weak anomalous fermion number violation, thermal scattering, and a new method for computing \cp\ violating processes during the transition. We can account for the observed baryon asymmetry, provided new \cp-violating phases are greater than $\sim 10~{-(3-5)}$, and some superpartners are light enough to be relevant during the transition, which takes place at a temperature of (50-100) GeV. In one case the light superpartners are the charginos and/or the neutralinos; in another case the top squarks and both Higgs doublets are light. Our calculation is easily extended to the case of a general two Higgs model, where we find sufficient baryogenesis provided the Higgs potential contains a phase of order $ 5\times10~{-4}$.

Journal ArticleDOI
TL;DR: In this paper, a simple and well motivated global U(2) symmetry, acting on the lightest two generations, completely solves the flavour changing problem and necessarily leads to a predictive texture for the Yukawa couplings.

Journal ArticleDOI
TL;DR: In this paper, the possibility of creating baryon asymmetry at the electroweak phase transition in the minimal supersymmetric standard model is considered for the case when right-handed squarks are much lighter than left-handed ones.

Journal ArticleDOI
TL;DR: The charge transport mechanism of electroweak baryogenesis in a realistic two-Higgs-doublet model is quantitatively study and concludes that it is marginally strong enough to produce the observed baryon asymmetry of the universe.
Abstract: 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 do-main walls, and comparing the exact profile of the $\mathrm{CP}$-violating phase with a commonly used ansatz. We note that the phenomenon of spontaneous $\mathrm{CP}$ violation at high temperature can occur in this model, even when there is no $\mathrm{CP}$ 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 $\ensuremath{\tau}$ leptons from the wall gives the dominant effect. We conclude that this mechanism is at best marginally capable of producing the observed baryon asymmetry of the universe, and we discuss some ways in which it might be enhanced.

Journal ArticleDOI
TL;DR: The seeding of this turbulent field by the motion of the dipole charge layers in the phase transition bubble walls is discussed, and the strength of the produced fields is estimated.
Abstract: The electroweak phase transition, if proceeding through nucleation and growth of bubbles, should generate large scale turbulent flow, which in turn generates magnetic turbulence and hence magnetic fields on the scale of turbulence flow. We discuss the seeding of this turbulent field by the motion of the dipole charge layers in the phase transition bubble walls, and estimate the strength of the produced fields. \textcopyright{} 1996 The American Physical Society.

Posted Content
TL;DR: 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: This paper gives an analytic treatment of quantum mechanical reflection in the thin wall regime, in which interactions with the plasma can be neglected as a particle propagates across the wall, and calculates the baryon asymmetry for various parameter ranges and concludes that asymmetries comparable with observations can be generated.
Abstract: We investigate ``nonlocal'' schemes for baryogenesis at a first-order electroweak phase transition, in which the effects of a CP-violating condensate on the bubble wall propagate into the unbroken phase where the sphaleron rate is unsuppressed. Such a condensate exists in multi-Higgs-boson extensions of the standard model, and may exist due to an instability in the minimal standard model. In this paper we first discuss the general problem of determining the perturbations induced by a CP-violating condensate, distinguishing two regimes (quantum and classical). We then give an analytic treatment of quantum-mechanical reflection in the thin wall regime, in which interactions with the plasma can be neglected as a particle propagates across the wall. We focus on leptons because of their much weaker coupling to the plasma. We argue that they are likely to be accurately described by this calculation, but quarks are not. The relative magnitude of the baryon asymmetry produced for different fermions depends on their relative Yukawa couplings (not their zero temperature masses), their transport properties, and their interactions. We calculate the baryon asymmetry for various parameter ranges and conclude that asymmetries comparable with observations can be generated. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: This work identifies sensitive channels for new flavor physics involving the members of the third generation in concert with the adjoining generations, with potential novel effects in {ital b}-flavored and charm physics.
Abstract: In strong dynamical schemes for electroweak symmetry breaking the third generation must be treated in a special manner, owing to the heavy top quark. This potentially leads to new flavor physics involving the members of the third generation in concert with the adjoining generations, with potential novel effects in b-flavored and charm physics. We give a general discussion and formulation of this kind of physics, abstracted largely from top-color models which we elaborate in detail. We identify sensitive channels for such new physics accessible to current and future experiments. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: This work investigates baryogenesis at a first-order electroweak phase transition in the presence of a CP-violating condensate on the bubble walls, in the regime in which thebubble walls are ``thick,'' in the sense that fermions interact with the plasma many times as the bubble wall passes.
Abstract: We investigate baryogenesis at a first-order electroweak phase transition in the presence of a CP-violating condensate on the bubble walls, in the regime in which the bubble walls are ``thick,'' in the sense that fermions interact with the plasma many times as the bubble wall passes. Such a condensate is present in multi-Higgs-doublet extensions of the standard model and may be formed via an instability in the minimal standard model. We concentrate on particles with typical thermal energies in the plasma, whose interactions with the wall are accurately described by the WKB approximation, in which a classical chiral force is evident. The deviations from thermal equilibrium produced by the motion of the wall are then treated using a classical Boltzmann equation which we solve in a fluid approximation. From the resulting equations we find two effects important for baryogenesis: (i) a classical chiral force term due to the CP-violating background and (ii) a term arising from hypercharge-violating interactions which are pushed out of equilibrium by the background field. Provided the wall propagates slower than the speed of sound, both terms lead to the diffusion of a chiral asymmetry in front of the wall. This can produce a baryon asymmetry of the observed magnitude for typical wall velocities and thicknesses. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: Focusing on SU(5) or SO(10) unification, the relationship between the top and bottom masses and the superspectrum is analysed, and the phenomenological implications of the grand unified theory (GUT) conditions on scalar masses are analyzed.
Abstract: The consequences of assuming the third-generation Yukawa couplings are all large and comparable are studied in the context of the minimal supersymmetric extension of the standard model. General aspects of the renormalization group (RG) evolution of the parameters, theoretical constraints needed to ensure proper electroweak symmetry breaking, and experimental and cosmological bounds on low-energy parameters are presented. We also present complete and exact semianalytic solutions to the one-loop RG equations. Focusing on SU(5) or SO(10) unification, we analyse the relationship between the top and bottom masses and the superspectrum, and the phenomenological implications of the grand unified theory (GUT) conditions on scalar masses. Future experimental measurements of the superspectrum and of the strong coupling will distinguish between various GUT-scale scenarios. And if present experimental knowledge is to be accounted for most naturally, a particular set of predictions is singled out.

Journal ArticleDOI
TL;DR: In this article, the effects of the U(1) subgroup using lattice Monte Carlo techniques were studied. And they showed that the phase transition is stronger when the number of SU(2)−Higgs subgroups is larger than 1.
Abstract: The continuum 3d SU(2)$\times$U(1)+Higgs theory is an effective theory for a large class of 4d high-temperature gauge theories, including the minimal standard model and some of its supersymmetric extensions. We study the effects of the U(1) subgroup using lattice Monte Carlo techniques. When $g'^2/g^2$ is increased from the zero corresponding to pure SU(2)+Higgs theory, the phase transition gets stronger. However, the increase in the strength is close to what is expected perturbatively, and the qualitative features of the phase diagram remain the same as for $g'^2=0$. In particular, the first order transition still disappears for $m_H>m_{H,c}$. We measure the photon mass and mixing angle, and find that the mass vanishes in both phases within the statistical errors.

Journal ArticleDOI
TL;DR: In this article, the observed hierarchy of quark and lepton masses and mixings may be obtained by adding an abelian family symmetry to the Minimal Supersymmetric Model and coupling quarks and leptons to an electroweak singlet scalar field.

Journal ArticleDOI
TL;DR: These constraints significantly restrict the category of admissible Grand Unified theories, but are quite compatible with recently proposed effects whereby superconducting strings may have been formed close to the electroweak phase transition.
Abstract: We investigate the cosmological consequences of particle physics theories that admit stable loops of superconducting cosmic string - {\it vortons}. General symmetry breaking schemes are considered, in which strings are formed at one energy scale and subsequently become superconducting in a secondary phase transition at what may be a considerably lower energy scale. We estimate the abundances of the ensuing vortons, and thereby derive constraints on the relevant particle physics models from cosmological observations. These constraints significantly restrict the category of admissible Grand Unified theories, but are quite compatible with recently proposed effects whereby superconducting strings may have been formed close to the electroweak phase transition.

Journal ArticleDOI
TL;DR: In this article, two-loop corrections to the finite-temperature effective potential in the MSSM can have a dramatic effect on the strength of the electroweak phase transition, making it more strongly first order.

Journal ArticleDOI
TL;DR: In this paper, the mass ranges of new neutral gauge bosons and constraints on the accompanying exotic particles as predicted by a class of superstring models are addressed, and it is shown that breaking of an additional U(1)′ symmetry is radiative when the appropriate Yukawa couplings of exotic particles are of order one, analogous to the radiative breaking of the electroweak symmetry in the supersymmetric standard model due to the large top-quark Yukawa coupling.
Abstract: We address the mass ranges of new neutral gauge bosons and constraints on the accompanying exotic particles as predicted by a class of superstring models. Under certain assumptions about the supersymmetry breaking parameters we show that breaking of an additional U(1)′ symmetry is radiative when the appropriate Yukawa couplings of exotic particles are of order one, analogous to the radiative breaking of the electroweak symmetry in the supersymmetric standard model due to the large top-quark Yukawa coupling. Such large Yukawa couplings occur for a large class of string models. The Z′ and exotic masses are either of , or of a scale intermediate between the string and electroweak scales. In the former case, may be achieved without excessive fine-tuning, and is within future experimental reach.

Journal ArticleDOI
TL;DR: In this article, the authors explore the phenomenology of gauge-mediated SUSY-breaking scenarios with a large hierarchy of Higgs VEVs, and show the possibility of large deviations (in the direction currently favored by experiment) from standard-model and small $tan\beta$ predictions.
Abstract: We explore some topics in the phenomenology of gauge-mediated SUSY-breaking scenarios having a large hierarchy of Higgs VEVs, $v_U/v_D = tan\beta \gg 1$. Some motivation for this scenario is first presented. We then use a systematic, analytic expansion (including some threshold corrections) to calculate the $\mu$ parameter needed for proper electroweak breaking and the radiative corrections to the B parameter, which fortuitously cancel at leading order. If B = 0 at the messenger scale then $tan\beta$ is naturally large and calculable; we calculate it. We then confront this prediction with classical and quantum vacuum stability constraints arising from the Higgs-slepton potential, and indicate the preferred values of the top quark mass and messenger scale(s). The possibility of vacuum instability in a different direction yields an upper bound on the messenger mass scale complementary to the familiar bound from gravitino relic abundance. Next, we calculate the rate for $b\to s\gamma$ and show the possibility of large deviations (in the direction currently favored by experiment) from standard-model and small $tan\beta$ predictions. Finally, we discuss the implications of these findings and their applicability to future, broader and more detailed investigations.


Journal ArticleDOI
TL;DR: HECTOR as discussed by the authors is a Fortran program for semi-analytical calculations of radiative QED, QCD, and electroweak corrections to the double-differential cross sections of NC and CC deep inelastic charged lepton proton (or lepton deuteron) scattering.

Journal ArticleDOI
TL;DR: In this paper, the authors used the tunneling criterion for the existence of a first order electroweak phase change and showed that strong first order phase change occurs in about 50% of cases.