27 research outputs found
Constraining anisotropic models of the early Universe with WMAP9 data
We constrain several models of the early Universe that predict a statistical
anisotropy of the cosmic microwave background (CMB) sky. We make use of WMAP9
maps deconvolved with beam asymmetries. As compared to previous releases of
WMAP data, they do not exhibit the anomalously large quadrupole of statistical
anisotropy. This allows to strengthen the limits on the parameters of models
established earlier in the literature. In particular, the amplitude of the
special quadrupole is constrained as |g_*|<0.072 at 95% C.L. (-0.046<g_*<0.048
at 68% C.L.) independently of the preferred direction in the sky. The upper
limit is obtained on the total number of e-folds in anisotropic inflation with
the Maxwellian term nonminimally coupled to the inflaton, namely N_{tot}
<N_{CMB} +82 at 95% C.L. (+14 at 68% C.L.) for N_{CMB}=60. We also constrain
models of the (pseudo)conformal universe. The strongest constraint is obtained
for spectator scenarios involving a long stage of subhorizon evolution after
conformal rolling, which reads h^2 < 0.006 at 95% C.L., in terms of the
relevant parameter. The analogous constraint is much weaker in dynamical
models, e.g., Galilean genesis.Comment: 28 pages, 8 figures; references added, matches published versio
Constraints on violation of Lorentz invariance from atmospheric showers initiated by multi-TeV photons
We discuss the effect of hypothetical violation of Lorentz invariance at high
energies on the formation of atmospheric showers by very-high-energy gamma
rays. In the scenario where Lorentz invariance violation leads to a decrease of
the photon velocity with energy the formation of the showers is suppressed
compared to the Lorentz invariant case. Absence of such suppression in the
high-energy part of spectrum of the Crab nebula measured independently by HEGRA
and H.E.S.S. collaborations is used to set lower bounds on the energy scale of
Lorentz invariance violation. These bounds are competitive with the strongest
existing constraints obtained from timing of variable astrophysical sources and
the absorption of TeV photons on the extragalactic background light. They will
be further improved by the next generation of multi-TeV gamma-ray
observatories.Comment: 21 pages, 4 figures. References adde
Prospective constraints on Lorentz violation from ultrahigh-energy photon detection
We point out that violation of Lorentz invariance affects the interaction of
high-energy photons with the Earth's atmosphere and magnetic field. In certain
parameter region this interaction becomes suppressed and the photons escape
observation passing through the atmosphere without producing air showers. We
argue that a detection of photon-induced air showers with energies above 10^19
eV, implying the absence of suppression as well as the absence of photon decay,
will put tight double-sided limits on Lorentz violation in the sector of
quantum electrodynamics. These constraints will be by several orders of
magnitude stronger than the existing ones and will be robust against any
assumptions about the astrophysical origin of the detected photons.Comment: 6 pages, revtex; significant additions compared to the previous
versio
Revisiting constraints on the (pseudo)conformal universe with Planck data
We revisit constraints on the (pseudo)conformal universe from the nonobservation of statistical anisotropy in the Planck data. The quadratic maximal likelihood estimator is applied to the Planck temperature maps at frequencies 143 and 217 GHz as well as their cross-correlation. The strongest constraint is obtained in the scenario of the (pseudo)conformal universe with a long intermediate evolution after conformal symmetry breaking. In terms of the relevant parameter (coupling constant), the limit is h2<0.0013 at 95% C.L. (using the cross estimator). The analogous limit is much weaker in the scenario without the intermediate stage (h2lnH0Λ<0.52) allowing the coupling constant to be of order 1. In the latter case, the non-Gaussianity in the four-point function appears to be a more promising signature.SCOPUS: ar.jinfo:eu-repo/semantics/publishe