1,088 research outputs found
Consistency of Relevant Cosmological Deformations on all Scales
Using cosmological perturbation theory we show that the most relevant defor-
mation of gravity is consistent at the linear level. In particular, we prove
the absence of uni- tarity violating negative norm states in the weak coupling
regime from sub- to super-Hubble scales. This demonstrates that the recently
proposed classical self-protection mechanism of deformed gravity extends to the
entire kinematical domain.Comment: 22 pages, 4 figure
Cosmic Attractors and Gauge Hierarchy
We suggest a new cosmological scenario which naturally guarantees the
smallness of scalar masses and VEVs, without invoking supersymmetry or any
other (non-gravitationaly coupled) new physics at low energies. In our
framework, the scalar masses undergo discrete jumps due to nucleation of closed
branes during (eternal) inflation. The crucial point is that the step size of
variation decreases in the direction of decreasing scalar mass. This scenario
yields exponentially large domains with a distribution of scalar masses, which
is sharply peaked around a hierarchically small value of the mass. This value
is the "attractor point" of the cosmological evolution
Predictive Power of Strong Coupling in Theories with Large Distance Modified Gravity
We consider theories that modify gravity at cosmological distances, and show
that any such theory must exhibit a strong coupling phenomenon, or else it is
either inconsistent or is already ruled out by the solar system observations.
We show that all the ghost-free theories that modify dynamics of spin-2
graviton on asymptotically flat backgrounds, automatically have this property.
Due to the strong coupling effect, modification of the gravitational force is
source-dependent, and for lighter sources sets in at shorter distances. This
universal feature makes modified gravity theories predictive and potentially
testable not only by cosmological observations, but also by precision
gravitational measurements at scales much shorter than the current cosmological
horizon. We give a simple parametrization of consistent large distance modified
gravity theories and their predicted deviations from the Einsteinian metric
near the gravitating sources.Comment: 12 pages, Latex, to be published in New Journal of Physic
CP Violation from Dimensional Reduction: Examples in 4+1 Dimensions
We provide simple examples of the generation of complex mass terms and hence
CP violation through dimensional reduction.Comment: 6 pages, typos corrected, 1 reference adde
Supersymmetry breaking and loop corrections at the end of inflation
We show that quantum corrections to the effective potential in supersymmetric
hybrid inflation can be calculated all the way from the inflationary period -
when the Universe is dominated by a false vacuum energy density - till the
fields settle down to the global supersymmetric minimum of the potential. These
are crucial for getting a continuous description of the evolution of the
fields.Comment: minor corrections; version to be published in Phys. Rev.
Cosmic D--term Strings as Wrapped D3 Branes
We describe cosmic D--term strings as D3 branes wrapped on a resolved
conifold. The matter content that gives rise to D--term strings is shown to
describe the world--volume theory of a space--filling D3 brane transverse to
the conifold which itself is a wrapped D5 brane. We show that, in this brane
theory, the tension of the wrapped D3 brane mathces that of the D--term string.
We argue that there is a new type of cosmic string which arises from fractional
D1 branes on the world--volume of a fractional D3 brane.Comment: 13 pages in phyzzx.tex; eq. (17) corrected, other minor corrections;
v3: more minor correction
The Accelerated Universe and the Moon
Cosmologically motivated theories that explain small acceleration rate of the
Universe via modification of gravity at very large, horizon or super-horizon
distances, can be tested by precision gravitational measurements at much
shorter scales, such as the Earth-Moon distance. Contrary to the naive
expectation the predicted corrections to the Einsteinian metric near
gravitating sources are so significant that fall within sensitivity of the
proposed Lunar Ranging experiments. The key reason for such corrections is the
van Dam-Veltman-Zakharov discontinuity present in linearized versions of all
such theories, and its subsequent absence at the non-linear level ala
Vainshtein
Black Hole Formation and Classicalization in Ultra-Planckian 2 -> N Scattering
We establish a connection between the ultra-Planckian scattering amplitudes
in field and string theory and unitarization by black hole formation in these
scattering processes. Using as a guideline an explicit microscopic theory in
which the black hole represents a bound-state of many soft gravitons at the
quantum critical point, we were able to identify and compute a set of
perturbative amplitudes relevant for black hole formation. These are the
tree-level N-graviton scattering S-matrix elements in a kinematical regime
(called classicalization limit) where the two incoming ultra-Planckian
gravitons produce a large number N of soft gravitons. We compute these
amplitudes by using the Kawai-Lewellen-Tye relations, as well as scattering
equations and string theory techniques. We discover that this limit reveals the
key features of the microscopic corpuscular black hole N-portrait. In
particular, the perturbative suppression factor of a N-graviton final state,
derived from the amplitude, matches the non-perturbative black hole entropy
when N reaches the quantum criticality value, whereas final states with
different value of N are either suppressed or excluded by non-perturbative
corpuscular physics. Thus we identify the microscopic reason behind the black
hole dominance over other final states including non-black hole classical
object. In the parameterization of the classicalization limit the scattering
equations can be solved exactly allowing us to obtain closed expressions for
the high-energy limit of the open and closed superstring tree-level scattering
amplitudes for a generic number N of external legs. We demonstrate matching and
complementarity between the string theory and field theory in different large-s
and large-N regimes.Comment: 55 pages, 7 figures, LaTeX; v2: typos removed; final version to
appear in Nucl. Phys.
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
The Power of Brane-Induced Gravity
We study the role of the brane-induced graviton kinetic term in theories with
large extra dimensions. In five dimensions we construct a model with a
TeV-scale fundamental Planck mass and a {\it flat} extra dimension the size of
which can be astronomically large. 4D gravity on the brane is mediated by a
massless zero-mode, whereas the couplings of the heavy Kaluza-Klein modes to
ordinary matter are suppressed. The model can manifest itself through the
predicted deviations from Einstein theory in long distance precision
measurements of the planetary orbits. The bulk states can be a rather exotic
form of dark matter, which at sub-solar distances interact via strong 5D
gravitational force. We show that the induced term changes dramatically the
phenomenology of sub-millimeter extra dimensions. For instance, high-energy
constraints from star cooling or cosmology can be substantially relaxed.Comment: 24 pages, 4 eps figures; v2 typos corrected; v3 1 ref. added; PRD
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