37,663 research outputs found

    Radiative Electroweak Symmetry-Breaking Revisited

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    In the absence of a tree-level scalar-field mass, renormalization-group methods permit the explicit summation of leading-logarithm contributions to all orders of the perturbative series within the effective potential for SU(2)×U(1)SU(2)\times U(1) electroweak symmetry. This improvement of the effective potential function is seen to reduce residual dependence on the renormalization mass scale. The all-orders summation of leading logarithm terms involving the dominant three couplings contributing to radiative corrections is suggestive of a potential characterized by a plausible Higgs boson mass of 216 GeV. However, the tree potential's local minimum at ϕ=0\phi =0 is restored if QCD is sufficiently strong.Comment: revtex, 4 pages, 1 eps figure embedded in manuscript. Updated version contains additional comments and corrects minor error

    Dark energy from conformal symmetry breaking

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    The breakdown of conformal symmetry in a conformally invariant scalar-tensor gravitational model is revisited in the cosmological context. Although the old scenario of conformal symmetry breaking in cosmology containing scalar field has already been used in many earlier works, it seems that no special attention has been paid for the investigation on the possible connection between the breakdown of conformal symmetry and the existence of dark energy. In this paper, it is shown that the old scenario of conformal symmetry breaking in cosmology, if properly interpreted, not only has a potential ability to describe the origin of dark energy as a symmetry breaking effect, but also may resolve the coincidence problem.Comment: 11 pages, minor revision, published online in EPJ

    Charge symmetry breaking in Λ\Lambda hypernuclei revisited

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    The large charge symmetry breaking (CSB) implied by the Λ\Lambda binding energy difference ΔBΛ4(0g.s.+)≡BΛ(Λ4\Delta B^{4}_{\Lambda}(0^+_{\rm g.s.})\equiv B_{\Lambda}(_{\Lambda}^4He)−-BΛ(Λ4B_{\Lambda}(_{\Lambda}^4H) = 0.35±\pm0.06 MeV of the A=4A=4 mirror hypernuclei ground states, determined from emulsion studies, has defied theoretical attempts to reproduce it in terms of CSB in hyperon masses and in hyperon-nucleon interactions, including one pion exchange arising from Λ−Σ0\Lambda-\Sigma^0 mixing. Using a schematic strong-interaction ΛN↔ΣN\Lambda N\leftrightarrow\Sigma N coupling model developed by Akaishi and collaborators for ss-shell Λ\Lambda hypernuclei, we revisit the evaluation of CSB in the A=4A=4 Λ\Lambda hypernuclei and extend it to pp-shell mirror Λ\Lambda hypernuclei. The model yields values of ΔBΛ4(0g.s.+)∼0.25\Delta B^{4}_{\Lambda} (0^+_{\rm g.s.})\sim 0.25 MeV. Smaller size and mostly negative pp-shell binding energy differences are calculated for the A=7−10A=7-10 mirror hypernuclei, in rough agreement with the few available data. CSB is found to reduce by almost 30 keV the 110 keV  Λ10_{~\Lambda}^{10}B g.s. doublet splitting anticipated from the hyperon-nucleon strong-interaction spin dependence, thereby explaining the persistent experimental failure to observe the 2exc−→1g.s.−2^-_{\rm exc}\to 1^-_{\rm g.s.} γ\gamma-ray transition.Comment: a few clarifying statements added to v2; matches published PLB version plus a note added after publication on p.1

    Chiral symmetry breaking with no bilinear condensate revisited

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    While chiral symmetry breaking in the QCD vacuum is attributed to nonzero chiral condensate, an alternative symmetry breaking pattern with no chiral condensate is also possible, as pointed out by Stern. This hypothetical phase was excluded in QCD at zero density long time ago, but nothing forbids it at finite baryon density. In this work, we study the θ\theta dependence of this unorthodox phase on the basis of chiral perturbation theory. Physical observables such as energy density, topological susceptibility, non-local chiral order parameter and meson masses are computed analytically in the epsilon-regime. At nonzero θ\theta we find an exotic phase that breaks vectorial flavor symmetries in a way analogous to the Aoki phase in lattice QCD.Comment: 27 pages, 8 figures. v2: minor revisions, published versio

    Chiral symmetry breaking revisited: the gap equation with lattice ingredients

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    We study chiral symmetry breaking in QCD, using as ingredients in the quark gap equation recent lattice results for the gluon and ghost propagators. The Ansatz employed for the quark-gluon vertex is purely non-Abelian, introducing a crucial dependence on the ghost dressing function and the quark-ghost scattering amplitude. The numerical impact of these quantities is considerable: the need to invoke confinement explicitly is avoided, and the dynamical quark masses generated are of the order of 300 MeV. In addition, the pion decay constant and the quark condensate are computed, and are found to be in good agreement with phenomenology.Comment: 3 pages, 5 figures. Talk presented at the Quark Confinement and the Hadron Spectrum - Madrid 2010, August 30th - September 3rd 2010, Madrid, Spai

    Parisi Phase in a Neuron

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    Pattern storage by a single neuron is revisited. Generalizing Parisi's framework for spin glasses we obtain a variational free energy functional for the neuron. The solution is demonstrated at high temperature and large relative number of examples, where several phases are identified by thermodynamical stability analysis, two of them exhibiting spontaneous full replica symmetry breaking. We give analytically the curved segments of the order parameter function and in representative cases compute the free energy, the storage error, and the entropy.Comment: 4 pages in prl twocolumn format + 3 Postscript figures. Submitted to Physical Review Letter
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