23 research outputs found
Vacuum pressure, dark energy and dark matter
It has been argued that the correct, i.e. positive, sign of quantum vacuum
energy density, or more properly, negative sign of quantum vacuum pressure,
requires not a very large number, e.g. ~100, of additional, undiscovered
fundamental bosonic particle species, absent in the standard model.
Interpretation of the new particle species in terms of dark matter ones permits
to qualitatively, and even quantitatively, connect all the three concepts given
in the title.Comment: 6 pages, 0 figure
Induced gauge interactions revisited
It has been shown that the old-fashioned idea of Sakharov's induced gravity
and gauge interactions in the "one-loop dominance" version works astonishingly
well yielding reasonable parameters. It appears that induced coupling constants
of gauge interactions of the standard model assume qualitatively realistic
values. Moreover, it is possible to induce the Barbero--Immirzi parameter of
canonical gravity from the fields entering the standard model.Comment: 13 page
Estimation of the height of the first interaction in gamma-ray showers observed by Cherenkov telescopes
Very high energy gamma rays entering the atmosphere initiate Extensive Air
Showers (EAS). The Cherenkov light induced by an EAS can be observed by
ground-based telescopes to study the primary gamma rays. An important parameter
of an EAS, determining its evolution, is the height of the first interaction of
the primary particle. However, this variable cannot be directly measured by
Cherenkov telescopes. We study two simple, independent methods for the
estimation of the first interaction height. We test the methods using the Monte
Carlo simulations for the 4 Large Size Telescopes (LST) that are part of the
currently constructed Cherenkov Telescope Array (CTA) Observatory. We find that
using such an estimated parameter in the gamma/hadron separation can bring a
mild improvement (~10-20%) in the sensitivity in the energy range ~30-200 GeV.Comment: 8 pages, 6 figures, accepted for publication in Astroparticle Physic
Studies of the nature of the low-energy, gamma-like background for Cherenkov Telescope Array
The upcoming Cherenkov Telescope Array (CTA) project is expected to provide
unprecedented sensitivity in the low-energy ( <~100 GeV) range for Cherenkov
telescopes. In order to exploit fully the potential of the telescopes the
standard analysis methods for gamma/hadron separation might need to be revised.
We study the composition of the background by identifying events composed
mostly of a single electromagnetic subcascade or double subcascade from a
{\pi}0 (or another neutral meson) decay. We apply the standard simulation and
analysis chain of CTA to evaluate the potential of the standard analysis to
reject such events.Comment: All CTA contributions at arXiv:1709.03483. Proc. of the 35th
International Cosmic Ray Conference, Busan, Kore
Quantization of four-dimensional Abelian gravity
An abelian version of standard general relativity in the Cartan-Palatini
gauge-like formulation in four dimensions has been introduced. Traditional
canonical analysis utilizing similarities to the akin Husain-Kuchar SU(2)
version of gravity has been performed. The model has been next quantized in the
canonical path-integral Faddeev-Popov formalism yielding abelian BF theory.Comment: Minor changes, additional symmetry discussed. 5 pages, 2 columns,
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An analysis method for data taken by Imaging Air Cherenkov Telescopes at very high energies under the presence of clouds
The effective observation time of Imaging Air Cherenkov Telescopes (IACTs) plays an important role in the detection of γ-ray sources, especially when the expected flux is low. This time is strongly limited by the atmospheric conditions. Significant extinction of Cherenkov light caused by the presence of clouds reduces the photon detection rate and also complicates or even makes impossible proper data analysis. However, for clouds with relatively high atmospheric transmission, high energy showers can still produce enough Cherenkov photons to allow their detection by IACTs. In this paper, we study the degradation of the detection capability of an array of small-sized telescopes for different cloud transmissions. We show the expected changes of the energy bias, energy and angular resolution and the effective collection area caused by absorption layers located at 2.5 and 4.5 km above the observation level. We demonstrate simple correction methods for reconstructed energy and effective collection area. As a result, the source flux that is observed during the presence of clouds is determined with a systematic error of 20%. Finally, we show that the proposed correction method can be used for clouds at altitudes higher than 5 km a.s.l. As a result, the analysis of data taken under certain cloudy conditions will not require additional time- consuming Monte Carlo simulations
Geometry of the X-ray source 1H 0707–495
Aims. We investigate the constraints on the size and location of the X-ray source in 1H 0707–495 determined from the shape of the relativistically smeared reflection from the accretion disc. Methods. We developed a new code to model an extended X-ray source and we applied this code to all archival XMM observations of 1H 0707–495. Results. In contrast to earlier works we find that the relativistic reflection in this source is not consistent with an extended uniform corona. Instead, we find that the X-ray source must be very compact, at most a gravitational radius in size, and located at most a few gravitational radii from the black-hole horizon. A uniform extended corona produces an emissivity that is similar to a twice-broken power-law, but the inner emissivity is fixed by the source geometry rather than being a free parameter. In 1H0707–495, the reflection from the inner disc is much stronger than expected for a uniformly extended source. Including the effect of ionised absorption from the wind does not change this conclusion, but including scattered emission (and more complex absorption) from the wind can dramatically change the reflection parameters