arXiv subjects

S. V. Troitsky

Publications and source records attributed to S. V. Troitsky.

At least 73 records · Page 4Linked to original sources

arXiv2008

Global anisotropy of arrival directions of ultra-high-energy cosmic rays: capabilities of space-based detectors

Planned space-based ultra-high-energy cosmic-ray detectors (TUS, JEM-EUSO and S-EUSO) are best suited for searches of global anisotropies in the distribution of arrival directions of cosmic-ray particles because they will be able to observe the full sky with a single instrument. We calculate quantitatively the strength of anisotropies associated with two models of the origin of the highest-energy particles: the extragalactic model (sources follow the distribution of galaxies in the Universe) and the superheavy dark-matter model (sources follow the distribution of dark matter in the Galactic halo). Based on the expected exposure of the experiments, we estimate the optimal strategy for efficient search of these effects.

astro-ph↗

arXiv2008

Muon content of ultra-high-energy air showers: Yakutsk data versus simulations

We analyse a sample of 33 extensive air showers (EAS) with estimated primary energies above 2\cdot 10^{19} eV and high-quality muon data recorded by the Yakutsk EAS array. We compare, event-by-event, the observed muon density to that expected from CORSIKA simulations for primary protons and iron, using SIBYLL and EPOS hadronic interaction models. The study suggests the presence of two distinct hadronic components, ``light'' and ``heavy''. Simulations with EPOS are in a good agreement with the expected composition in which the light component corresponds to protons and the heavy component to iron-like nuclei. With SYBILL, simulated muon densities for iron primaries are a factor of \sim 1.5 less than those observed for the heavy component, for the same electromagnetic signal. Assuming two-component proton-iron composition and the EPOS model, the fraction of protons with energies E>10^{19} eV is 0.52^{+0.19}_{-0.20} at 95% confidence level.

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arXiv2007

Air-shower simulations with and without thinning: artificial fluctuations and their suppression

The most common way to simplify extensive Monte-Carlo simulations of air showers is to use the thinning approximation. We study its effect on the physical parameters reconstructed from simulated showers. To this end, we have created a library of showers simulated without thinning with energies from 10^17 eV to 10^18 eV, various zenith angles and primaries. This library is publicly available. Physically interesting applications of the showers simulated without thinning are discussed. Observables reconstructed from these showers are compared to those obtained with the thinning approximation. The amount of artificial fluctuations introduced by thinning is estimated. A simple method, multisampling, is suggested which results in a controllable suppression of artificial fluctuations and at the same time requires less demanding computational resources as compared to the usual thinning.

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arXiv2007

Towards event-by-event studies of the ultrahigh-energy cosmic-ray composition

We suggest a method which improves the precision of studies of the primary composition of ultra-high-energy cosmic rays. Two principal ingredients of the method are (1) comparison of the observed and simulated parameters for individual showers, without averaging over arrival directions and (2) event-by-event selection of simulated showers by the physical observables and not by the reconstructed primary parameters. A detailed description of the algorithm is presented and illustrated by several examples.

astro-ph↗

arXiv2007

Constraining the fraction of primary gamma rays at ultra-high energies from the muon data of the Yakutsk extensive-air-shower array

By making use of the data on the total signal and on the muon component of the air showers detected by the Yakutsk array, we analyze, in the frameworks of the recently suggested event-by-event approach, how large the fraction of primary gamma-rays at ultra-high energies can be. We derive upper limits on the photon fraction in the integral flux of primary cosmic rays. At the 95% confidence level (CL), these limits are 22% for primary energies E_0>4\cdot 10^{19}eV and 12% for E_0>2\cdot 10^{19}eV. Despite the presence of muonless events, the data are consistent with complete absence of photons at least at 95% CL. The sensitivity of the results to systematic uncertainties, in particular to those of the energy determination for non-photon primaries, is discussed.

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arXiv2006

Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data

We present the interpretation of the muon and scintillation signals of ultra-high-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest energy events with known muon content and conclude that at the 95% confidence level (C.L.) none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.

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arXiv2005

Estimate of the correlation signal between cosmic rays and BL Lacs in future data

The existing correlation between BL Lacertae objects (BL Lacs) and cosmic-ray events observed by HiRes experiment provide sufficient information to formulate quantitatively the hypothesis about the flux of neutral cosmic-ray particles originated from BL Lacs. We determine the potential of future cosmic ray experiments to test this hypothesis by predicting the number of coincidences between arrival directions of cosmic rays and positions of BL Lacs on the celestial sphere, which should be observed in the future datasets. We find that the early Pierre Auger data will not have enough events to address this question. On the contrary, the final Pierre Auger data and the early Telescope Array data will be sufficient to fully test this hypothesis. If confirmed, it would imply the existence of highest-energy neutral particles coming from cosmological distances.

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arXiv2005

Identification of extragalactic sources of the highest energy EGRET photons by correlation analysis

We found significant correlations between the arrival directions of the highest energy photons (E>10 GeV) observed by EGRET and positions of the BL Lac type objects (BL Lacs). The observed correlations imply that not less than three per cent of extragalactic photons at these energies originate from BL Lacs. Some of the correlating BL Lacs have no counterparts in the EGRET source catalog, i.e. do not coincide with strong emitters of gamma-rays at lower energy. The study of correlating BL Lacs suggests that they may form a subset which is statistically different from the total BL Lac catalog; we argue that they are prominent candidates for TeV gamma-ray sources. Our results demonstrate that the analysis of positional correlations is a powerful approach indispensable in cases when low statistics limits or even prohibits the standard case-by-case identification.

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arXiv2005

Magnetic deflections and possible sources of the ultra-high-energy cosmic rays in the AGASA-HiRes-Yakutsk cluster

The cluster of ultra-high-energy cosmic rays observed by the AGASA, HiRes and Yakutsk experiments is studied with respect to possible deflections of particles in regular magnetic fields. Best-fit positions of a potential source of these clustered particles are found, with account of the errors in energy estimation, both in the frameworks of particular models of the Galactic magnetic field and treating the direction and the amount of deflection as free parameters. The study suggests that an unknown regular component of either Galactic or extragalactic magnetic field may dominate over modelled components in the direction of the cluster. Possible sources of the cosmic rays in that direction are considered.

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arXiv2004

A comparative study of correlations between arrival directions of ultra-high-energy cosmic rays and positions of their potential astrophysical sources

We consider various classes of persistent extragalactic astrophysical sources which have been suggested in literature as possible emitters of ultra-high-energy cosmic rays (UHECR). We compare the strength of the claimed correlations by a uniform procedure for all classes of sources by making use of the AGASA, Yakutsk and HiRes stereo data. BL Lac type objects correlate with the cosmic rays detected by all three independent experiments and are more probably, compared to other astrophysical sources, related to the UHECR origin. With the account of the Galactic magnetic field (not possible for the HiRes data at the moment), apart of BL Lac type objects, unidentified gamma-ray sources may be correlated with AGASA and Yakutsk cosmic rays.

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arXiv2004

Testing the correlations between ultra-high-energy cosmic rays and BL Lac type objects with HiRes stereoscopic data

Previously suggested correlations of BL Lac type objects with the arrival directions of the ultra-high-energy cosmic ray primaries are tested by making use of the HiRes stereoscopic data. The results of the study support the conclusion that BL Lacs may be the cosmic ray sources and suggest the presence of a small (a few percent) fraction of neutral primaries at E>10^{19} eV.

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arXiv2004

Searching for family-number conserving neutral gauge bosons from extra dimensions

Previous studies have shown how the three generations of the Standard Model fermions can arise from a single generation in more than four dimensions, and how off-diagonal neutral couplings arise for gauge-boson Kaluza-Klein recurrences. These couplings conserve family number in the leading approximation. While an existing example, built on a spherical geometry, suggests a high compactification scale, we conjecture that the overall structure is generic, and work out possible signatures at colliders, compatible with rare decays data.

hep-ph↗

arXiv2004

Flavour violation with a single generation

We calculate probabilities of flavour violating processes mediated by Kalutza-Klein modes of gauge bosons in a model where three generations of the Standard Model fermions arise from a single generation in (5+1) dimensions. We discuss a distinctive feature of the model: while the processes in which the generation number $G$ changes are strongly suppressed, the model is constrained by those with $ΔG=0$, for instance $K\to μ^\pm e^\mp$. The bound on the size of the extra dimensions is $1/R \gtrsim 64$ TeV.

hep-ph↗

arXiv2003

Declination dependence of the cosmic-ray flux at extreme energies

We study the large-scale distribution of the arrival directions of the highest energy cosmic rays observed by various experiments. Despite clearly insufficient statistics, we find a deficit of cosmic rays at energies higher than 10^{20} eV from a large part of the sky around the celestial North Pole. We speculate on possible explanations of this feature.

astro-ph↗

arXiv2003

Fermions in the vortex background on a sphere

In 5+1 dimensions, we construct a vortex-like solution on a two-dimensional sphere. We study fermionic zero modes in the background of this solution and relate them to the replication of fermion families in the Standard Model. In particular, using a compactified space removes the need for the difficult localisation of gauge fields, while the present procedure (rather than naive compactification on a disk) also removes spurious fermionic modes.

hep-ph↗

arXiv2002

Long-lived neutralino and ultra-high energy cosmic rays

Secondary photons from decays of metastable neutralinos can contribute to the ultra-high energy cosmic ray flux. The neutralino production rate is too low in acceleration mechanisms to affect the cosmic ray spectrum without emitting enormous energy in photons and neutrinos. However, in top-down models with sources not concentrated in galactic halos, neutralino decays change the spectrum significantly. We estimate the parameters of a model in which photons from neutralino decays are responsible for cosmic ray events with energies above 10^20 eV, and figure out distinctive experimental signatures for this model.

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arXiv2002

Constraints on ultra-high energy neutrinos from optically thick astrophysical accelerators

The Z-burst mechanism invoked to explain ultra-high energy cosmic rays is severely constrained by measurements of the cosmic gamma-ray background by EGRET. We discuss the case of optically thick sources and show that jets and hot spots of active galaxies cannot provide the optical depth required to suppress the photon flux. Other extragalactic accelerators (AGN cores and sites of gamma ray bursts), if they are optically thick, could be tested by future measurements of the secondary neutrino flux.

astro-ph↗

arXiv2001

Neutrino masses with a single generation in the bulk

In a class of multidimensional models, topology of the thick brane provides three chiral fermionic families with hierarchical masses and mixings in the effective four-dimensional theory, while the full model contains a single vector-like generation. We discuss how to incorporate three non-degenerate neutrino masses in these models with the help of only one singlet bulk fermion.

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