10,791 research outputs found
CMB B-modes, spinorial space-time and Pre-Big Bang (II)
The BICEP2 collaboration reported recently a B-mode polarization of the
cosmic microwave background (CMB) radiation inconsistent with the null
hypothesis at a significance of > 5 {\sigma}. This result has been often
interpreted as a signature of primordial gravitational waves from cosmic
inflation, even if actually polarized dust emission may be at the origin of
such a signal. Even assuming that part of this CMB B-mode polarization really
corresponds to the early Universe dynamics, its interpretation in terms of
inflation and primordial gravitational waves is not the only possible one.
Alternative cosmologies such as pre-Big Bang patterns and the spinorial
space-time (SST) we introduced in 1996-97 can naturally account for such CMB
B-modes. In particular, the SST automatically generates a privileged space
direction (PSD) whose existence may have been confirmed by Planck data. If such
a PSD exists, it seems normal to infer that vector perturbations have been
present in the early Universe leading to CMB B-modes in suitable cosmological
patterns. Inflation would not be required to explain the BICEP2 result assuming
it really contains a primordial signal. More generally, pre-Big Bang
cosmologies can also generate gravitational waves in the early Universe without
any need for cosmic inflation. We further discuss here possible alternatives to
the inflationary interpretation of a primordial B-mode polarization of cosmic
microwave background radiation.Comment: 11 page
Testing fundamental principles with high-energy cosmic rays
It is not yet clear whether the observed flux suppression for ultra-high
energy cosmic rays (UHECR) at energies above \simeq 4.10E19 eV is a signature
of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or corresponds, for instance, to
the maximum energies available at the relevant sources. Both phenomena can be
sensitive to violations of standard special relativity modifying cosmic-ray
propagation or acceleration at very high energy, and would in principle allow
to set bounds on Lorentz symmetry violation (LSV) parameters. But the precise
phenomenological analysis of the experimental data is far from trivial, and
other effects can be present. The effective parameters can be directly linked
to Planck-scale physics or to physics beyond Planck scale. If a vacuum rest
frame (VRF) exists, LSV can modify the internal structure of particles at very
high energy. Conventional symmetries may also cease to be valid at energies
close to the Planck scale. Other possible violations of fundamental principles
and conventional basic hypotheses (quantum mechanics, quark confinement, energy
and momentum conservation, vacuum homogeneity and "static" properties,
effective space dimensions...) can also be considered and possibly tested in
high-energy cosmic-ray experiments. Even below UHE (ultra-high energy), exotic
signatures cannot be excluded. We present an updated discussion of the
theoretical and phenomenological situation, including prospects for earth-based
and space experiments and a simple potential interpretation of the observed
UHECR composition in terms of LSV where the GZK cutoff would be replaced by
spontaneous emission of photons or e+ e- pairs. As the OPERA result on a
possible superluminal propagation of the muon neutrino was announced after the
conference, we briefly comment on the consistency problems that a \simeq 2.5 x
10E-5 critical speed anomaly for the muon neutrino can raise.Comment: 4 pages, Proceedings of the XXIst International Europhysics
Conference on High Energy Physics, Grenoble, France, July 2011. To be
published by Proceedings of Science (already available
Lorentz violation, vacuum, cosmic rays, superbradyons and Pamir data
The possibility that Pamir data at very high energy cannot be fully explained
by standard physics has recently led to the suggestion that the peculiar jet
structure observed above ~ 10E16 eV could be due to a suppression of effective
space transverse dimensions. The new pattern considered violates Lorentz
symmetry. We point out that, in models with Lorentz symmetry violation, a
suppression of available transverse energy for jets while conserving
longitudinal momentum can be generated by new forms of energy losses at very
high energy without altering space-time structure. An illustrative example can
be superbradyon emission, where in all cases the superbradyon energy would be
much larger than its momentum times c (speed of light). More generally, such
phenomena could be due to the interaction of the high-energy cosmic ray with
new vacuum and/or particle structure below the 10E-20 cm scale. Scenarios
involving Lorentz symmetry violation but not superbradyons are also briefly
considered.Comment: 7 pages, enlarged versio
Physics Opportunities Above the Greisen-Zatsepin-Kuzmin Cutoff: Lorentz Symmetry Violation at the Planck Scale
Special relativity has been tested at low energy with great accuracy, but
these results cannot be extrapolated to very high-energy phenomena: this new
domain of physics may actually provide the key to the, yet unsettled, question
of the ether and the absolute rest frame. Introducing a critical distance
scale, a, below 10E-25 cm (the wavelength scale of the highest-energy observed
cosmic rays) allows to consider models, compatible with standard tests of
special relativity, where a small violation of Lorentz symmetry (a can, for
instance, be the Planck length) leads to a deformed relativistic kinematics
(DRK) producing dramatic effects on the properties of very high-energy cosmic
rays. For instance, the Greisen-Zatsepin-Kuzmin (GZK) cutoff does no longer
apply and particles which are unstable at low energy (neutron, some hadronic
resonances like the Delta++, possibly several nuclei...) become stable at very
high energy. In these models, an absolute local rest frame exists (the vacuum
rest frame, VRF) and special relativity is a low-momentum limit. We discuss the
possible effects of Lorentz symmetry violation (LSV) on kinematics and
dynamics, as well as the cosmic-ray energy range (well below the energy scale
associated to the fundamental length) and experiments (on earth and from space)
where they could be detected.Comment: 11 pages, LaTeX, requires aipproc.sty; invited talk at the Workshop
on "Observing Giant Cosmic Ray Air Showers for > 10E20 eV Particles from
Space", Univ. of Maryland, Nov 13-15, 199
Lorentz Symmetry Violation and High-Energy Cosmic Rays
We discuss possible violations of Poincare's relativity principle at energy
scales close to Planck scale and point out the potentialities of high-energy
cosmic-ray physics to uncover these new phenomena.Comment: Talk given at the Workshop on "Topics in Astroparticle and
Underground Physics", Gran Sasso September 1997. 3 pages, LaTex, uses
espcrc2.st
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