31,092 research outputs found
Virtual QCD corrections to Higgs boson plus four parton processes
We report on the calculation of virtual processes contributing to the
production of a Higgs boson and two jets in hadron-hadron collisions. The
coupling of the Higgs boson to gluons, via a virtual loop of top quarks, is
treated using an effective theory, valid in the large top quark mass limit. The
calculation is performed by evaluating one-loop diagrams in the effective
theory. The primary method of calculation is a numerical evaluation of the
virtual amplitudes as a Laurent series in , where is the
dimensionality of space-time. For the cases and we confirm the numerical results by an explicit analytic
calculation.Comment: 21 pages, 2 figures. v2 modifies the text to agree with published
version and corrects typos in the analytical expressions for the four quark
amplitude
A cosmic equation of state for the inhomogeneous Universe: can a global far-from-equilibrium state explain Dark Energy?
A system of effective Einstein equations for spatially averaged scalar
variables of inhomogeneous cosmological models can be solved by providing a
`cosmic equation of state'. Recent efforts to explain Dark Energy focus on
`backreaction effects' of inhomogeneities on the effective evolution of
cosmological parameters in our Hubble volume, avoiding a cosmological constant
in the equation of state. In this Letter it is argued that, if kinematical
backreaction effects are indeed of the order of the averaged density (or larger
as needed for an accelerating domain of the Universe), then the state of our
regional Hubble volume would have to be in the vicinity of a
far-from-equilibrium state that balances kinematical backreaction and average
density. This property, if interpreted globally, is shared by a stationary
cosmos with effective equation of state . It
is concluded that a confirmed explanation of Dark Energy by kinematical
backreaction may imply a paradigmatic change of cosmology.Comment: 7 pages, matches published version in Class. Quant. Gra
Local freedom in the gravitational field
In a cosmological context, the electric and magnetic parts of the Weyl
tensor, E_{ab} and H_{ab}, represent the locally free curvature - i.e. they are
not pointwise determined by the matter fields. By performing a complete
covariant decomposition of the derivatives of E_{ab} and H_{ab}, we show that
the parts of the derivative of the curvature which are locally free (i.e. not
pointwise determined by the matter via the Bianchi identities) are exactly the
symmetrised trace-free spatial derivatives of E_{ab} and H_{ab} together with
their spatial curls. These parts of the derivatives are shown to be crucial for
the existence of gravitational waves.Comment: New results on gravitational waves included; new references added;
revised version (IOP style) to appear Class. Quantum Gra
Ten bar probe technical summary
The feasibility of an outer planet common atmospheric probe is studied with emphasis on entry heating rates and improved ephemeris. It is concluded that a common probe design is possible except for Jupiter; the basic technology exists except for Jupiter heat shielding. A Mariner class bus provides for better bus science and probe bus communications than a Pioneer class bus
General relativistic analysis of peculiar velocities
We give a careful general relativistic and (1+3)-covariant analysis of
cosmological peculiar velocities induced by matter density perturbations in the
presence of a cosmological constant. In our quasi-Newtonian approach,
constraint equations arise to maintain zero shear of the non-comoving
fundamental worldlines which define a Newtonian-like frame, and these lead to
the (1+3)-covariant dynamical equations, including a generalized Poisson-type
equation. We investigate the relation between peculiar velocity and peculiar
acceleration, finding the conditions under which they are aligned. In this case
we find (1+3)-covariant relativistic generalizations of well-known Newtonian
results.Comment: 8 pages, LaTeX2e (iopart); minor changes, matches version accepted
for publication by Classical and Quantum Gravit
Speed of light in the extended gravity theories
We shall investigate the possibility of formulation of varying speed of light
(VSL) in the framework of Palatini non-linear Ricci scalar and Ricci squared
theories. Different speeds of light including the causal structure constant,
electromagnetic, and gravitational wave speeds are discussed. We shall see that
two local frames are distinguishable and discuss about the velocity of light in
these two frames. We shall investigate which one of these local frames is
inertial.Comment: 19 pages. to appear in Classical Quantum Gravit
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