76 research outputs found
Improved Effective Potential in Curved Spacetime and Quantum Matter - Higher Derivative Gravity Theory
\noindent{\large\bf Abstract.} We develop a general formalism to study the
renormalization group (RG) improved effective potential for renormalizable
gauge theories ---including matter--gravity--- in curved spacetime. The
result is given up to quadratic terms in curvature, and one-loop effective
potentials may be easiliy obtained from it. As an example, we consider scalar
QED, where dimensional transmutation in curved space and the phase structure of
the potential (in particular, curvature-induced phase trnasitions), are
discussed. For scalar QED with higher-derivative quantum gravity (QG), we
examine the influence of QG on dimensional transmutation and calculate QG
corrections to the scalar-to-vector mass ratio. The phase structure of the
RG-improved effective potential is also studied in this case, and the values of
the induced Newton and cosmological coupling constants at the critical point
are estimated. Stability of the running scalar coupling in the Yukawa theory
with conformally invariant higher-derivative QG, and in the Standard Model with
the same addition, is numerically analyzed. We show that, in these models, QG
tends to make the scalar sector less unstable.Comment: 23 pages, Oct 17 199
Astrophysical structures from primordial quantum black holes
The characteristic sizes of astrophysical structures, up to the whole
observed Universe, can be recovered, in principle, assuming that gravity is the
overall interaction assembling systems starting from microscopic scales, whose
order of magnitude is ruled by the Planck length and the related Compton
wavelength. This result agrees with the absence of screening mechanisms for the
gravitational interaction and could be connected to the presence of Yukawa
corrections in the Newtonian potential which introduce typical interaction
lengths. This result directly comes out from quantization of primordial black
holes and then characteristic interaction lengths directly emerge from quantum
field theory.Comment: 11 page
A Phenomenological Analysis of Gluon Mass Effects in Inclusive Radiative Decays of the and $\Upsilon
The shapes of the inclusive photon spectra in the processes \Jp \to \gamma
X and \Up \to \gamma X have been analysed using all available experimental
data.
Relativistic, higher order QCD and gluon mass corrections were taken into
account in the fitted functions. Only on including the gluon mass corrections,
were consistent and acceptable fits obtained. Values of
GeV and GeV were found for the
effective gluon masses (corresponding to Born level diagrams) for the \Jp and
\Up respectively. The width ratios \Gamma(V \to {\rm hadrons})/\Gamma(V \to
\gamma+ {\rm hadrons}) V=\Jp, \Up were used to determine and . Values consistent with the current world
average were obtained only when gluon mass correction factors,
calculated using the fitted values of the effective gluon mass, were applied. A
gluon mass GeV, as suggested with these results, is consistent with
previous analytical theoretical calculations and independent phenomenological
estimates, as well as with a recent, more accurate, lattice calculation of the
gluon propagator in the infra-red region.Comment: 50 pages, 11 figures, 15 table
Towards resolution of the enigmas of P-wave meson spectroscopy
The mass spectrum of P-wave mesons is considered in a nonrelativistic
constituent quark model. The results show the common mass degeneracy of the
isovector and isodoublet states of the scalar and tensor meson nonets, and do
not exclude the possibility of a similar degeneracy of the same states of the
axial-vector and pseudovector nonets. Current experimental hadronic and \tau
-decay data suggest, however, a different scenario leading to the a_1 meson
mass \simeq 1190 MeV and the K_{1A}-K_{1B} mixing angle \simeq (37\pm 3)^o.
Possible s\bar{s} states of the four nonets are also discussed.Comment: 22 pages, LaTe
The Scientific Foundations of Forecasting Magnetospheric Space Weather
The magnetosphere is the lens through which solar space weather phenomena are focused and directed towards the Earth. In particular, the non-linear interaction of the solar wind with the Earth's magnetic field leads to the formation of highly inhomogenous electrical currents in the ionosphere which can ultimately result in damage to and problems with the operation of power distribution networks. Since electric power is the fundamental cornerstone of modern life, the interruption of power is the primary pathway by which space weather has impact on human activity and technology. Consequently, in the context of space weather, it is the ability to predict geomagnetic activity that is of key importance. This is usually stated in terms of geomagnetic storms, but we argue that in fact it is the substorm phenomenon which contains the crucial physics, and therefore prediction of substorm occurrence, severity and duration, either within the context of a longer-lasting geomagnetic storm, but potentially also as an isolated event, is of critical importance. Here we review the physics of the magnetosphere in the frame of space weather forecasting, focusing on recent results, current understanding, and an assessment of probable future developments.Peer reviewe
Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of its Environment
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