arXiv subjects

W. Buchmüller

Publications and source records attributed to W. Buchmüller.

24 records · Page 2Linked to original sources

arXiv1998

Quark Lepton Mass Hierarchies and the Baryon Asymmetry

The mass hierarchies of quarks and charged leptons as well as a large $\n_\m$-$\n_\t$ mixing angle are naturally explained by the Frogatt-Nielsen mechanism with a nonparallel family structure of chiral charges. We extend this mechanism to right-handed neutrinos. Their out-of-equilibrium decay generates a cosmological baryon asymmetry whose size is quantized in powers of the hierarchy parameter $\e^2$. For the simplest hierarchy pattern the neutrino mass $\bar{m}_\n= (m_{\n_\m}m_{\n_\t})^{1/2} \sim 10^{-2}$ eV, which is inferred from present indications for neutrino oscillations, implies a baryon asymmetry $n_B/s \sim 10^{-10}$. The corresponding baryogenesis temperature is $T_B \sim 10^{10}$ GeV.

hep-ph↗

arXiv1998

Baryon Asymmetry and Dark Matter

We study the implications of a large baryogenesis temperature, $T_B = O(10^{10}$ GeV), on the mass spectrum of superparticles in supersymmetric extensions of the standard model. Models with a neutralino as lightest superparticle (LSP) are excluded. A consistent picture is obtained with the gravitino as LSP, followed by a higgsino-like neutralino (NSP). Gravitinos with masses from 10 to 100 GeV may be the dominant component of dark matter.

hep-ph↗

arXiv1996

Magnetic Screening in the High Temperature Phase of the Standard Model

Non-perturbative effects in the high-temperature phase of the electroweak theory are characterized by a magnetic screening length. Its size influences the range of validity of perturbation theory, and it also determines the critical Higgs boson mass where the first-order phase transition changes to a crossover. We propose a gauge-invariant definition of the magnetic screening length and discuss its role in several gauge-dependent and gauge-invariant correlation functions.

hep-ph↗

arXiv1993

Aspects of the Cosmological Electroweak Phase Transition

We study the decay of the metastable symmetric phase in the standard model at finite temperature. For the SU(2)-Higgs model the two wave function correction terms $Z_{\vp}(\vp^2,T)$ and $Z_χ(\vp^2,T)$ of Higgs and Goldstone boson fields are calculated to one-loop order. We find that the derivative expansion of the effective action is reliable for Higgs masses smaller than the W-boson mass. We propose a new procedure to evaluate the decay rate by first integrating out the vector field and the components of the scalar fields with non-zero Matsubara frequencies. The static part of the scalar field is treated in the saddle point approximation. As a by-product we obtain a formula for the decay rate of a homogeneous unstable state. The course of the cosmological electroweak phase transition is evaluated numerically for different Higgs boson masses and non-vanishing magnetic mass of the gauge boson. For Higgs masses above $\sim 60$ GeV the latent heat can reheat the system to the critical temperature which qualitatively changes the nature of the transition.

hep-ph↗

arXiv1993

Searching for Supersymmetry in High-Energy Photon-Proton Scattering

We investigate the possibility to search for supersymmetry in the scattering of protons and Compton back-scattered laser light. We evaluate the cross sections for inelastic and elastic production of wino pairs for different electron-proton c.m.s. energies. For $\sqrt{s}=1\ TeV$ the cross section exceeds $1\ fb$ for $m_w<190\ GeV$.

hep-ph↗

arXiv1993

The weak electroweak phase transition

We present a detailed analysis of the phase transition in the standard model at finite temperature. Using an improved perturbation theory, where plasma masses are determined from a set of one-loop gap equations, we evaluate the effective potential $V_{eff}(φ,T)$ in next-to-leading order, i.e., including terms cubic in the gauge coupling $g$, the scalar self-coupling $λ^{1/2}$ and the top-quark Yukawa coupling $f_t$. The gap equations yield a non-vanishing magnetic plasma mass for the gauge bosons, originating from the non-abelian self-interactions. We discuss in detail size and origin of higher order effects and conclude that the phase transition is weakly first-order up to Higgs masses of about $70\ GeV$, above which our calculation is no longer self-consistent. For larger Higgs masses even an approximation containing all $g^4$ contributions to $V_{eff}$ is not sufficient, at least a full calculation to order $g^6$ is needed. These results turn out to be rather insensitive to the top-quark mass in the range $m_t=100\ -\ 180\ GeV$. Using Langer's theory of metastability we calculate the nucleation rate of critical droplets and discuss some aspects of the cosmological electroweak phase transition.

hep-ph↗