32,756 research outputs found
Scale Invariance without Inflation?
We propose a new alternative mechanism to seed a scale invariant spectrum of
primordial density perturbations that does not rely on inflation. In our
scenario, a perfect fluid dominates the early stages of an expanding,
non-inflating universe. Because the speed of sound of the fluid decays,
perturbations are left frozen behind the sound horizon, with a spectral index
that depends on the fluid equation of state. We explore here a toy model that
realizes this idea. Although the model can explain an adiabatic, Gaussian,
scale invariant spectrum of primordial perturbations, it turns out that in its
simplest form it cannot account for the observed amplitude of the primordial
density perturbations.Comment: 6 two-column pages, 1 figure. Uses RevTeX4. v2: References added and
number of required e-folds refine
Scale-invariance of galaxy clustering
Some years ago we proposed a new approach to the analysis of galaxy and
cluster correlations based on the concepts and methods of modern statistical
Physics. This led to the surprising result that galaxy correlations are fractal
and not homogeneous up to the limits of the available catalogs. The usual
statistical methods, which are based on the assumption of homogeneity, are
therefore inconsistent for all the length scales probed so far, and a new, more
general, conceptual framework is necessary to identifythe real physical
properties of these structures. In the last few years the 3-d catalogs have
been significatively improved and we have extended our methods to the analysis
of number counts and angular catalogs. This has led to a complete analysis of
all the available data that we present in this review. The result is that
galaxy structures are highly irregular and self-similar: all the available data
are consistent with each other and show fractal correlations (with dimension ) up to the deepest scales probed so far (1000 \hmp) and even more
as indicated from the new interpretation of the number counts. The evidence for
scale-invariance of galaxy clustering is very strong up to 150 \hmp due to
the statistical robustness of the data but becomes progressively weaker
(statistically) at larger distances due to the limited data. In These facts
lead to fascinating conceptual implications about our knowledge of the universe
and to a new scenario for the theoretical challenge in this field.Comment: Latex file 165 pages, 106 postscript figures. This paper is also
available at http://www.phys.uniroma1.it/DOCS/PIL/pil.html To appear in
Physics Report (Dec. 1997
Emerging Universe from Scale Invariance
We consider a scale invariant model which includes a term in action
and show that a stable "emerging universe" scenario is possible. The model
belongs to the general class of theories, where an integration measure
independent of the metric is introduced. To implement scale invariance (S.I.),
a dilaton field is introduced. The integration of the equations of motion
associated with the new measure gives rise to the spontaneous symmetry breaking
(S.S.B) of S.I. After S.S.B. of S.I. in the model with the term (and
first order formalism applied), it is found that a non trivial potential for
the dilaton is generated. The dynamics of the scalar field becomes non linear
and these non linearities are instrumental in the stability of some of the
emerging universe solutions, which exists for a parameter range of the theory.Comment: 21 pages, 4 figures. Accepted for publication in JCA
Scale Invariance + Unitarity => Conformal Invariance?
We revisit the long-standing conjecture that in unitary field theories, scale
invariance implies conformality. We explain why the Zamolodchikov-Polchinski
proof in D=2 does not work in higher dimensions. We speculate which new ideas
might be helpful in a future proof. We also search for possible
counterexamples. We consider a general multi-field scalar-fermion theory with
quartic and Yukawa interactions. We show that there are no counterexamples
among fixed points of such models in 4-epsilon dimensions. We also discuss fake
counterexamples, which exist among theories without a stress tensor.Comment: 17p
Inflation from Broken Scale Invariance
We construct a model of inflation based on a low-energy effective theory of
spontaneously broken global scale invariance. This provides a shift symmetry
that protects the inflaton potential from quantum corrections. Since the
underlying scale invariance is non-compact, arbitrarily large inflaton field
displacements are readily allowed in the low-energy effective theory. A weak
breaking of scale invariance by almost marginal operators provides a
non-trivial inflaton minimum, which sets and stabilizes the final low-energy
value of the Planck scale. The underlying scale invariance ensures that the
slow-roll approximation remains valid over large inflaton displacements, and
yields a scale invariant spectrum of perturbations as required by the CMB
observations.Comment: 18 pages, 3 figure
Scale Invariance and Vacuum Energy
The possibility of mass in the context of scale-invariant, generally
covariant theories, is discussed. Scale invariance is considered in the context
of a gravitational theory where the action, in the first order formalism, is of
the form + where is
a density built out of degrees of freedom independent of the metric. For global
scale invariance, a "dilaton" has to be introduced, with non-trivial
potentials = in and =
in . This leads to non-trivial mass generation and
a potential for which is interesting for new inflation. Scale invariant
mass terms for fermions lead to a possible explanation of the present day
accelerated universe and of cosmic coincidences.Comment: Essay awarded an honorable mention in the 1999 Gravity Research
Foundation Competition, Published in Mod. Phys. Lett. A14: 1397 (1999
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