57 research outputs found
General Results on Glueball Masses in QCD
A number of authors have investigated mass inequalities for mesons and baryons in QCD. These provide rigorous nonperturbative constraints on the mass spectrum. Similar inequalities for glueballs are investigated. For nonzero spin J, in the large-Nc approximation, mJ - ⩾ mJ+ is found. (For J = 0, the existence of a gluon condensate can modify this statement.) There are also constraints on how fast mJ can grow with J. For example, for mJ = a + bJα, 0 ⩽ α ⩽ 1 is found, a result consistent with Regge behaviour
Hadronic interactions, precocious unification, and cosmic ray showers at Auger energies
At Auger energies only model predictions enable us to extract primary cosmic
ray features. The simulation of the shower evolution depends sensitively on the
first few interactions, necessarily related to the quality of our understanding
of high energy hadronic collisions. Distortions of the standard ``soft
semi-hard'' scenario include novel large compact dimensions and a string or
quantum gravity scale not far above the electroweak scale. Na\"{\i}vely, the
additional degrees of freedom yield unification of all forces in the TeV range.
In this article we study the influence of such precocious unification during
atmospheric cascade developments by analyzing the most relevant observables in
proton induced showers.Comment: 16 pages latex. 4 eps figure
Neutrino-Induced Giant Air Showers in Large Extra Dimension Models
In models based on large extra dimensions where massive spin 2 exchange can
dominate at high energies, the neutrino-proton cross section can rise to
typical hadronic values at energies above 10^20 eV. The neutrino then becomes a
candidate for the primary that initiates the highest energy cosmic ray showers.
We investigate characteristics of neutrino-induced showers compared to
proton-induced showers. The comparison includes study of starting depth,
profile with depth, lateral particle distribution at ground and muon lateral
distribution at ground level. We find that for cross sections above 20 mb there
are regions of parameter space where the two types of showers are essentially
indistinguishable. We conclude that the neutrino candidate hypothesis cannot be
ruled out on the basis of shower characteristics.Comment: 24 pages, latex, 19 figures; text discussion and references added,
typos corrected; figures and conclusions unchange
Quantum power correction to the Newton law
We have found the graviton contribution to the one-loop quantum correction to
the Newton law. This correction results in interaction decreasing with distance
as 1/r^3 and is dominated numerically by the graviton contribution. The
previous calculations of this contribution to the discussed effect are
demonstrated to be incorrect.Comment: 10 pages, 5 figures; numerical error corrected, few references adde
Vanishing of cosmological constant in nonfactorizable geometry
We generalize the results of Randall and Sundrum to a wider class of
four-dimensional space-times including the four-dimensional Schwarzschild
background and de Sitter universe. We solve the equation for graviton
propagation in a general four dimensional background and find an explicit
solution for a zero mass bound state of the graviton. We find that this zero
mass bound state is normalizable only if the cosmological constant is strictly
zero, thereby providing a dynamical reason for the vanishing of cosmological
constant within the context of this model. We also show that the results of
Randall and Sundrum can be generalized without any modification to the
Schwarzschild background.Comment: 8 Pages(expanded version), Accepted in Phys. Rev.
Geodesics, gravitons and the gauge fixing problem
When graviton loops are taken into account, the background metric obtained as
a solution to the one-loop corrected Einstein equations turns out to be gauge
fixing dependent. Therefore it is of no physical relevance. Instead we consider
a physical observable, namely the trajectory of a test particle in the presence
of gravitons. We derive a quantum corrected geodesic equation that includes
backreaction effects and is explicitly independent of any gauge fixing
parameter.Comment: 21 pages, no figures, RevTe
UV-Completion by Classicalization
We suggest a novel approach to UV-completion of a class of non-renormalizable
theories, according to which the high-energy scattering amplitudes get
unitarized by production of extended classical objects (classicalons), playing
a role analogous to black holes, in the case of non-gravitational theories. The
key property of classicalization is the existence of a classicalizer field that
couples to energy-momentum sources. Such localized sources are excited in
high-energy scattering processes and lead to the formation of classicalons. Two
kinds of natural classicalizers are Nambu-Goldstone bosons (or, equivalently,
longitudinal polarizations of massive gauge fields) and scalars coupled to
energy-momentum type sources. Classicalization has interesting phenomenological
applications for the UV-completion of the Standard Model both with or without
the Higgs. In the Higgless Standard Model the high-energy scattering amplitudes
of longitudinal -bosons self-unitarize via classicalization, without the
help of any new weakly-coupled physics. Alternatively, in the presence of a
Higgs boson, classicalization could explain the stabilization of the hierarchy.
In both scenarios the high-energy scatterings are dominated by the formation of
classicalons, which subsequently decay into many particle states. The
experimental signatures at the LHC are quite distinctive, with sharp
differences in the two cases.Comment: 37 page
Classicalization of Gravitons and Goldstones
We establish a close parallel between classicalization of gravitons and
derivatively-coupled Nambu-Goldstone-type scalars. We show, that black hole
formation in high energy scattering process represents classicalization with
the classicalization radius given by Schwarzschild radius of center of mass
energy, and with the precursor of black hole entropy being given by number of
soft quanta composing this classical configuration. Such an entropy-equivalent
is defined for scalar classicalons also and is responsible for exponential
suppression of their decay into small number of final particles. This parallel
works in both ways. For optimists that are willing to hypothesize that gravity
may indeed self-unitarize at high energies via black hole formation, it
illustrates that the Goldstones may not be much different in this respect, and
they classicalize essentially by similar dynamics as gravitons. In the other
direction, it may serve as an useful de-mystifier of
via-black-hole-unitarization process and of the role of entropy in it, as it
illustrates, that much more prosaic scalar theories essentially do the same.
Finally, it illustrates that in both cases classicalization is the defining
property for unitarization, and that it sets-in before one can talk about
accompanying properties, such as entropy and thermality of static classicalons
(black holes). These properties are by-products of classicalization, and their
equivalents can be defined for non-gravitational cases of classicalization.Comment: 23 page
Effective Action for High-Energy Scattering in Gravity
The multi-Regge effective action is derived directly from the linearized
gravity action. After excluding the redundant field components we separate the
fields into momentum modes and integrate over modes which correspond neither to
the kinematics of scattering nor to the one of exchanged particles. The
effective vertices of scattering and of particle production are obtained as
sums of the contributions from the triple and quartic interaction terms and the
fields in the effective action are defined in terms of the two physical
components of the metric fluctuation.Comment: 15 pages, LATE
One-loop graviton corrections to Maxwell's equations
We compute the graviton induced corrections to Maxwell's equations in the
one-loop and weak field approximations. The corrected equations are analogous
to the classical equations in anisotropic and inhomogeneous media. We analyze
in particular the corrections to the dispersion relations. When the wavelength
of the electromagnetic field is much smaller than a typical length scale of the
graviton two-point function, the speed of light depends on the direction of
propagation and on the polarisation of the radiation. In the opposite case, the
speed of light may also depend on the energy of the electromagnetic radiation.
We study in detail wave propagation in two special backgrounds, flat
Robertson-Walker and static, spherically symmetric spacetimes. In the case of a
flat Robertson-Walker gravitational background we find that the corrected
electromagnetic field equations correspond to an isotropic medium with a
time-dependent effective refractive index. For a static, spherically symmetric
background the graviton fluctuations induce a vacuum structure which causes
birefringence in the propagation of light.Comment: 15 pages, revte
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