530,780 research outputs found

    A New Approach to Flavor Symmetry and an Extended Naturalness Principle

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    A class of non-supersymmetric extensions of the Standard Model is proposed in which there is a multiplicity of light scalar doublets in a multiplet of a non-abelian family group with the Standard Model Higgs doublet. Anthropic tuning makes the latter light, and consequently the other scalar doublets remain light because of the family symmetry. The family symmetry greatly constrains the pattern of FCNC and proton decay operators coming from scalar-exchange. Such models show that useful constraints on model-building can come from an extended naturalness principle when the electroweak scale is anthropically tuned.Comment: 31 pages, 3 figure

    Bond-order wave phase, spin solitons and thermodynamics of a frustrated linear spin-1/2 Heisenberg antiferromagnet

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    The linear spin-1/2 Heisenberg antiferromagnet with exchanges J1J_1, J2J_2 between first and second neighbors has a bond-order wave (BOW) phase that starts at the fluid-dimer transition at J2/J1=0.2411J_2/J_1 = 0.2411 and is particularly simple at J2/J1=1/2J_2/J_1 = 1/2. The BOW phase has a doubly degenerate singlet ground state, broken inversion symmetry and a finite energy gap EmE_m to the lowest triplet state. The interval 0.4<J2/J1<1.00.4<J_2/J_1<1.0 has large EmE_m and small finite size corrections. Exact solutions are presented up to N=28N=28 spins with either periodic or open boundary conditions and for thermodynamics up to N=18N=18. The elementary excitations of the BOW phase with large EmE_m are topological spin-1/2 solitons that separate BOWs with opposite phase in a regular array of spins. The molar spin susceptibility χM(T)\chi_M(T) is exponentially small for TEmT \ll E_m and increases nearly linearly with TT to a broad maximum. J1J_1, J2J_2 spin chains approximate the magnetic properties of the BOW phase of Hubbard-type models and provide a starting point for modeling alkali-TCNQ salts.Comment: 10 pages, 12 figure

    Random Isotropic Structures and Possible Glass Transitions in Diblock Copolymer Melts

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    We study the microstructural glass transitions in diblock-copolymer melts using a thermodynamic replica approach. Our approach performs an expansion in terms of the natural smallness parameter -- the inverse of the scaled degree of polymerization, which allows us to systematically study the approach to mean-field behavior as the degree of polymerization increases. We find that in the limit of infinite long polymer chains, both the onset of glassiness and the vitrification transition (Kauzmann temperature) collapse to the mean-field spinodal, suggesting that the spinodal can be regarded as the mean-field signature for glass transitions in this class of systems. We also study the order-disorder transitions (ODT) within the same theoretical framework; in particular, we include the leading-order fluctuation corrections due to the cubic interaction in the coarse-grained Hamiltonian, which has been ignored in previous works on the ODT in block copolymers. We find that the cubic term stabilizes both the ordered (body-centered-cubic) phase and the glassy state relative to the disordered phase. While in melts of symmetric copolymers the glass transition always occurs after the order-disorder transition (below the ODT temperature), for asymmetric copolymers, it is possible that the glass transition precedes the ordering transition.Comment: An error corrected in the referenc

    Nucleon-Nucleon Bremsstrahlung emission of massive Axion

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    We consider the problem of axion production by bremsstrahlung emission in a nuclear medium. The usual assumption of a massless axion is replaced by more general hypotheses, so that we can describe the emission process for axions with mass up to a few MeV. We point out that in certain physical situations the contribution from non-zero mass is non-negligible. In particular, in the mechanism for the production of Gamma Ray Bursts via emission of heavy axions the axion mass m_a ~ 1MeV is comparable with the temperature of the nuclear medium and thus can not be disregarded. Looking at our results we find, in fact, a fairly considerable reduction of the axion luminosity in that mechanism.Comment: 16 pages, 5 figure

    Behavior of X-Ray Dust Scattering and Implications for X-Ray Afterglows of Gamma-Ray Bursts

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    The afterglows of gamma-ray bursts (GRBs) have commonly been assumed to be due to shocks sweeping up the circum-stellar medium. However, most GRBs have been found in dense star-forming regions where a significant fraction of the prompt X-ray emission can be scattered by dust grains. Here we revisit the behavior of dust scattering of X-rays in GRBs. We find that the features of some X-ray afterglows from minutes to days after the gamma-ray triggers are consistent with the scattering of prompt X-ray emission from GRBs off host dust grains. This implies that some of the observed X-ray afterglows (especially those without sharp rising and decaying flares) could be understood with a dust-scattering--driven emission model.Comment: ApJ, in pres

    Analysis of the strong coupling constant GDsDsϕG_{D_{s}^{*}D_{s}\phi} and the decay width of DsDsγD_{s}^{*}\rightarrow D_{s}\gamma with QCD sum rules

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    In this article, we calculate the form factors and the coupling constant of the vertex DsDsϕD_{s}^{*}D_{s}\phi using the three-point QCD sum rules. We consider the contributions of the vacuum condensates up to dimension 77 in the operator product expansion(OPE). And all possible off-shell cases are considered, ϕ\phi, DsD_{s} and DsD_{s}^{*}, resulting in three different form factors. Then we fit the form factors into analytical functions and extrapolate them into time-like regions, which giving the coupling constant for the process. Our analysis indicates that the coupling constant for this vertex is GDsDsϕ=4.12±0.70GeV1G_{Ds*Ds\phi}=4.12\pm0.70 GeV^{-1}. The results of this work are very useful in the other phenomenological analysis. As an application, we calculate the coupling constant for the decay channel DsDsγD_{s}^{*}\rightarrow D_{s}\gamma and analyze the width of this decay with the assumption of the vector meson dominance of the intermediate ϕ(1020)\phi(1020). Our final result about the decay width of this decay channel is Γ=0.59±0.15keV\Gamma=0.59\pm0.15keV.Comment: arXiv admin note: text overlap with arXiv:1501.03088 by other author

    Review: The Powers of the Universe by Brian Swimme

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    This essay presents a review on Brian Swimme’s 3-DVD set of lecture series in the interdisciplinary field of philosophy, cosmology and consciousness. In the eleven 45-minute episodes of a systematic 9-hour immersive program, a set of 12 intercorrelated cosmological powers is proposed on the basis of modern scientific theory. A positive and life-affirming vision of human potential is attained together with a new level of ecological responsibility and relatedness. The interwoven cosmological paradigm compromises with two ancient eastern wisdoms
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