36,713 research outputs found
A Unitarity-Conserving Higgs Inflation Model
Scalar field models of inflation based on a large nonminimal coupling to
gravity xi, in particular, Higgs inflation, may violate unitarity at an energy
scale ~ M_p / xi << M_p. In this case the model is incomplete at energy scales
relevant to inflation. Here we propose a new unitarity-conserving model of
Higgs inflation. The completion of the theory is achieved via additional
interactions which are proportional to products of the derivatives of the Higgs
doublet. The resulting model differs from the original version of Higgs
inflation in its prediction for the spectral index, with a classical value n =
0.974. In the case of a nonsupersymmetric model, quantum corrections are likely
to strongly modify the tree-level potential, suggesting that supersymmetry or a
gauge singlet scalar inflaton is necessary for a completely successful model.Comment: 5 pages, published versio
Stress correlations in glasses
We rigorously establish that, in disordered three-dimensional (3D) isotropic
solids, the stress autocorrelation function presents anisotropic terms that
decay as at long-range, with the distance, as soon as either
pressure or shear stress fluctuations are normal. By normal, we mean that the
fluctuations of stress, as averaged over spherical domains, decay as the
inverse domain volume. Since this property is required for macroscopic stress
to be self-averaging, it is expected to hold generically in all glasses and we
thus conclude that the presence of stress correlation tails is the rule
in these systems. Our proof follows from the observation that, in an infinite
medium, when both material isotropy and mechanical balance hold, (i) the stress
autocorrelation matrix is completely fixed by just two radial functions: the
pressure autocorrelation and the trace of the autocorrelation of stress
deviators; furthermore, these two functions (ii) fix the decay of the
fluctuations of sphere-averaged pressure and deviatoric stresses for windows of
increasing volume. Our conclusion is reached because, due to the precise
analytic relation (i) fixed by isotropy and mechanical balance, the constraints
arising via (ii) from the normality of stress fluctuations demand the spatially
anisotropic stress correlation terms to decay as at long-range. For the
sake of generality, we also examine situations when stress fluctuations are not
normal
Spectral Variations in Early-Type Galaxies as a Function of Mass
We report on the strengths of three spectral indicators - Mg_2, Hbeta, and
Hn/Fe - in the integrated light of a sample of 100 field and cluster E/S0
galaxies. The measured indices are sensitive to age and/or and metallicity
variations within the galaxy sample. Using linear regression analysis for data
with non-uniform errors, we determine the intrinsic scatter present among the
spectral indices of our galaxy sample as a function of internal velocity
dispersion. Our analysis indicates that there is significantly more intrinsic
scatter in the two Balmer line indices than in the Mg_2 index, indicating that
the Balmer indices provide more dynamic range in determining the age of a
stellar population than does the Mg_2 index. Furthermore, the scatter is much
larger for the low velocity dispersion galaxies, indicating that star formation
has occurred more recently in the lower mass galaxies.Comment: 4 pages, 1 figure, 1 table, to appear in the Astrophysical Journal
Letter
A finite difference scheme for the equilibrium equations of elastic bodies
A compact difference scheme is described for treating the first-order system of partial differential equations which describe the equilibrium equations of an elastic body. An algebraic simplification enables the solution to be obtained by standard direct or iterative techniques
A compact finite difference scheme for div(Rho grad u) - q2u = 0
A representative class of elliptic equations is treated by a dissipative compact finite difference scheme and a general solution technique by relaxation methods is discussed in detail for the Laplace equation
Control of broad-area vertical-cavity surface emitting laser emission by optically induced photonic crystals
We control the emission properties of a broad-area vertical-cavity surface emitting laser by coupling it to an external feedback cavity containing a photorefractive crystal with an optically induced photonic lattice. The periodic modulation of the refractive index serves as a tunable filter and enables the dynamic suppression of unwanted spatial instabilities and modes, as originally suggested by Gomila et al
Gauge singlet scalar as inflaton and thermal relic dark matter
We show that, by adding a gauge singlet scalar S to the standard model which
is nonminimally coupled to gravity, S can act both as the inflaton and as
thermal relic dark matter. We obtain the allowed region of the (m_s, m_h)
parameter space which gives a spectral index in agreement with observational
bounds and also produces the observed dark matter density while not violating
vacuum stability or nonperturbativity constraints. We show that, in contrast to
the case of Higgs inflation, once quantum corrections are included the spectral
index is significantly larger than the classical value (n = 0.966 for N = 60)
for all allowed values of the Higgs mass m_h. The range of Higgs mass
compatible with the constraints is 145 GeV < m_h < 170 GeV. The S mass lies in
the range 45 GeV < ms < 1 TeV for the case of a real S scalar with large
quartic self-coupling lambdas, with a smaller upper bound for smaller lambdas.
A region of the parameter space is accessible to direct searches at the LHC via
h-->SS, while future direct dark matter searches should be able to
significantly constrain the model.Comment: 13 pages, 7 figures. Published versio
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