7,254 research outputs found

    Two-loop effective potential for a general renormalizable theory and softly broken supersymmetry

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    I compute the two-loop effective potential in the Landau gauge for a general renormalizable field theory in four dimensions. Results are presented for the \bar{MS} renormalization scheme based on dimensional regularization, and for the \bar{DR} and \bar{DR}' schemes based on regularization by dimensional reduction. The last of these is appropriate for models with softly broken supersymmetry, such as the Minimal Supersymmetric Standard Model. I find the parameter redefinition which relates the \bar{DR} and \bar{DR}' schemes at two-loop order. I also discuss the renormalization group invariance of the two-loop effective potential, and compute the anomalous dimensions for scalars and the beta function for the vacuum energy at two-loop order in softly broken supersymmetry. Several illustrative examples and consistency checks are included.Comment: 38 pages. Typos in equations (3.5), (3.11), and (6.3) are fixed. Explicit claim of renormalization group invariance in the general case of softly-broken supersymmetry is added. Additional discussion of cases of multiple simple or U(1) groups. Equations in Appendix B rewritten in a more useful for

    Self-consistently Improved Finite Temperature Effective Potential for Gauge Theories

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    The finite temperature effective potential of the Abelian Higgs Model is studied using the self-consistent composite operator method, which sums up the contributions of daisy and superdaisy diagrams. The effect of the momentum dependence of the effective masses is estimated by using a Rayleigh-Ritz variational approximation.Comment: 29 pages, 7 figures not included, Plain Tex, BUHEP-93-12, to appear in Physical Review D49. (additional comments on renormalization and a more quantitative comparison with previous results have been included, one more figure, two new references, two references updated

    Probing for Invisible Higgs Decays with Global Fits

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    We demonstrate by performing a global fit on Higgs signal strength data that large invisible branching ratios Br_{inv} for a Standard Model (SM) Higgs particle are currently consistent with the experimental hints of a scalar resonance at the mass scale m_h ~ 124 GeV. For this mass scale, we find Br_{inv} < 0.64 (95 % CL) from a global fit to individual channel signal strengths supplied by ATLAS, CMS and the Tevatron collaborations. Novel tests that can be used to improve the prospects of experimentally discovering the existence of a Br_{inv} with future data are proposed. These tests are based on the combination of all visible channel Higgs signal strengths, and allow us to examine the required reduction in experimental and theoretical errors in this data that would allow a more significantly bounded invisible branching ratio to be experimentally supported. We examine in some detail how our conclusions and method are affected when a scalar resonance at this mass scale has couplings deviating from the SM ones.Comment: 32pp, 15 figures v2: JHEP version, ref added & comment added after Eq.

    Wavepacket Dynamics in Yang-Mills Theory

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    We discuss the results of numerical simulations of colliding wavepackets in SU(2)SU(2) Yang--Mills theory. We investigate their behavior as a function of amplitude and momentum distribution. We find regions in our parameter space in which initial wave packets scatter into final configurations with dramatically different momentum distributions. These results constitute new classical trajectories with multiparticle boundary conditions. We explain their relevance for the calculation of scattering amplitudes in the semiclassical approximation. Finally, we give directions for future work.Comment: 11 pgs. text, 11 optional figs using PiCTeX and epsf, new version contains improved discussion of scaling properties of results and one additional figure

    Robust LHC Higgs Search in Weak Boson Fusion

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    We demonstrate that an LHC Higgs search in weak boson fusion production with subsequent decay to weak boson pairs is robust against extensions of the Standard Model or MSSM involving a large number of Higgs doublets. We also show that the transverse mass distribution provides unambiguous discrimination of a continuum Higgs signal from the Standard Model.Comment: 12p, 2 figs., additional comments on backgrounds, version to appear in PR

    Energy Budget of Cosmological First-order Phase Transitions

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    The study of the hydrodynamics of bubble growth in first-order phase transitions is very relevant for electroweak baryogenesis, as the baryon asymmetry depends sensitively on the bubble wall velocity, and also for predicting the size of the gravity wave signal resulting from bubble collisions, which depends on both the bubble wall velocity and the plasma fluid velocity. We perform such study in different bubble expansion regimes, namely deflagrations, detonations, hybrids (steady states) and runaway solutions (accelerating wall), without relying on a specific particle physics model. We compute the efficiency of the transfer of vacuum energy to the bubble wall and the plasma in all regimes. We clarify the condition determining the runaway regime and stress that in most models of strong first-order phase transitions this will modify expectations for the gravity wave signal. Indeed, in this case, most of the kinetic energy is concentrated in the wall and almost no turbulent fluid motions are expected since the surrounding fluid is kept mostly at rest.Comment: 36 pages, 14 figure

    Two-Higgs doublet models from TeV-scale supersymmetric extra U(1) models

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    We investigate the reduction of a general TeV-scale supersymmetric extra U(1) model to a 2HDM below the TeV- scale through the tree level non-decoupling. Portions of the parameter space of the extra U(1) model appropriate for obtaining a 2HDM are identified. Various properties of the resulting 2HDM are connected to the parameter space of the underlying model. PACS: 12.60.Jv, 12.60.Cn, 12.60.FrComment: 12 pages, 4 postscript figures, to appear in Phys. Rev.

    Plant height and hydraulic vulnerability to drought and cold

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    Understanding how plants survive drought and cold is increasingly important as plants worldwide experience dieback with drought in moist places and grow taller with warming in cold ones. Crucial in plant climate adaptation are the diameters of water-transporting conduits. Sampling 537 species across climate zones dominated by angiosperms, we find that plant size is unambiguously the main driver of conduit diameter variation. And because taller plants have wider conduits, and wider conduits within species are more vulnerable to conduction-blocking embolisms, taller conspecifics should be more vulnerable than shorter ones, a prediction we confirm with a plantation experiment. As a result, maximum plant size should be short under drought and cold, which cause embolism, or increase if these pressures relax. That conduit diameter and embolism vulnerability are inseparably related to plant size helps explain why factors that interact with conduit diameter, such as drought or warming, are altering plant heights worldwide
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