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P. Tinyakov

Publications and source records attributed to P. Tinyakov.

At least 19 recordsLinked to original sources
arXiv2025

New full-sky studies of the distribution of ultra-high-energy cosmic-ray arrival directions

Ground-based full-sky studies of the angular distribution of arrival directions of ultra-high-energy cosmic rays require combining data from different observatories, such as the Pierre Auger Observatory (Auger) and the Telescope Array (TA), because no single array can cover all declinations. A working group comprising members from the Auger and TA collaborations has been tasked with performing such studies for more than a decade and has found several indications of full-sky anisotropies. Here, we update the results for the large- and medium-scale anisotropy analyses using the latest data from TA, which include corrections for daily and yearly atmospheric effects in data for large-scale anisotropies and looser selection criteria in data for medium-scale anisotropies. We extend the latter one by considering two more galaxy catalogues, consisting of jetted or all AGNs. Finally we also introduce a new angular harmonic space analysis that allows us to measure both the auto-correlation and cross-correlation with all catalogues for all multipoles independently ($\ell_\text{max} = 20$ in this work) and scanning the energy threshold.

astro-ph.HE↗
arXiv2023

2022 report from the Auger-TA working group on UHECR arrival directions

After over 60 years, the powerful engines that accelerate ultra-high-energy cosmic rays (UHECRs) to the formidable energies at which we observe them from Earth remain mysterious. Assuming standard physics, we expect UHECR sources to lie within the local Universe (up to a few hundred~Mpc). The distribution of matter in the local Universe is anisotropic, and we expect this anisotropy to be imprinted on the distribution of UHECR arrival directions. Even though intervening intergalactic and Galactic magnetic fields deflect charged UHECRs and can distort these anisotropies, some amount of information on the distribution of the sources is preserved. In this proceedings contribution, we present the results of the joint Pierre Auger Observatory and Telescope Array searches for (a) the largest-scale anisotropies (the harmonic dipole and quadrupole) and (b) correlations with a sample of nearby starburst galaxies and the 2MRS catalogue tracing stellar mass within~250~Mpc. This analysis updates our previous results with the most recent available data, notably with the addition of 3~years of new Telescope Array data. The main finding is a correlation between the arrival directions of $12.1\%_{-3.1\%}^{+4.5\%}$~of UHECRs detected with $E \geq 38$~EeV by~Auger or with~$E \gtrsim 49$~EeV by~TA and the positions of nearby starburst galaxies on a ${15.1\text{deg}}_{-3.0\text{deg}}^{+4.6\text{deg}}$~angular scale, with a $4.7\sigma$~post-trial significance, up from $4.2\sigma$ obtained in our previous study.

astro-ph.HE↗
arXiv2022

Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers

The present white paper is submitted as part of the "Snowmass" process to help inform the long-term plans of the United States Department of Energy and the National Science Foundation for high-energy physics. It summarizes the science questions driving the Ultra-High-Energy Cosmic-Ray (UHECR) community and provides recommendations on the strategy to answer them in the next two decades.

astro-ph.HE↗
arXiv2021

Astroparticle physics with compact objects

Probing the existence of hypothetical particles beyond the Standard model often deals with extreme parameters: large energies, tiny cross-sections, large time scales, etc. Sometimes laboratory experiments can test required regions of parameter space, but more often natural limitations leads to poorly restrictive upper limits. In such cases astrophysical studies can help to expand the range of values significantly. Among astronomical sources, used in interests of fundamental physics, compact objects -- neutron stars and white dwarfs, -- play a leading role. We review several aspects of astroparticle physics studies related to observations and properties of these celestial bodies. Dark matter particles can be collected inside compact objects resulting in additional heating or collapse. We summarize regimes and rates of particle capturing as well as possible astrophysical consequences. Then we focus on a particular type of hypothetical particles -- axions. Their existence can be uncovered due to observations of emission originated due to Primakoff process in magnetospheres of neutron stars or white dwarfs. Alternatively, they can contribute to cooling of these compact objects. We present results in these areas, including upper limits based on recent observations.

astro-ph.HE↗
arXiv2020

Full-sky searches for anisotropies in UHECR arrival directions with the Pierre Auger Observatory and the Telescope Array

The arrival directions of ultra-high-energy cosmic rays appear to be approximately isotropically distributed over the whole sky, but the last-generation UHECR detector arrays, the Pierre Auger Observatory (Auger) and the Telescope Array (TA), have detected thousands of events, allowing us to study small deviations from isotropy. So far, Auger has detected a large-scale anisotropy consistent with a $\sim 6.5\%$ dipole moment in the distribution of cosmic rays with $E > 8$~EeV, and both collaborations have reported indications for smaller-scale anisotropies at higher energies. On the other hand, neither array has full-sky coverage, the Auger field of view being limited to declinations $\delta < +45^\circ$ and the TA one to $\delta > -16^\circ$. Searches for anisotropies with full-sky coverage thus require combining data from both arrays. A working group with members from both collaborations has been established for this task. Since even a minor systematic error in the energy determinations at either of the arrays could result in a sizeable spurious anisotropy along the north--south axis, we devised a method to cross-calibrate the energy scales of the two experiments with respect to each other by using events in a declination band within the intersection of their fields of view. In this contribution, we report on both updates on blind searches for anisotropies and the first full-sky studies of flux models based on possible local extragalactic sources.

astro-ph.HE↗
arXiv2019

Covering the celestial sphere at ultra-high energies

Despite deflections by Galactic and extragalactic magnetic fields, the distribution of ultra-high energy cosmic rays (UHECRs) over the celestial sphere remains a most promising observable for the identification of their sources. Thanks to a large number of detected events over the past years, a large-scale anisotropy at energies above 8 EeV has been identified, and there are also indications from the Telescope Array and Pierre Auger Collaborations of deviations from isotropy at intermediate angular scales (about 20 degrees) at the highest energies. In this contribution, we map the flux of UHECRs over the full sky at energies beyond each of two major features in the UHECR spectrum -- the ankle and the flux suppression --, and we derive limits for anisotropy on different angular scales in the two energy regimes. In particular, full-sky coverage enables constraints on low-order multipole moments without assumptions about the strength of higher-order multipoles. Following previous efforts from the two Collaborations, we build full-sky maps accounting for the relative exposure of the arrays and differences in the energy normalizations. The procedure relies on cross-calibrating the UHECR fluxes reconstructed in the declination band around the celestial equator covered by both observatories. We present full-sky maps at energies above 10 EeV and 50 EeV, using the largest datasets shared across UHECR collaborations to date. We report on anisotropy searches exploiting full-sky coverage and discuss possible constraints on the distribution of UHECR sources.

astro-ph.HE↗
arXiv2019

Search for a correlation between the UHECRs measured by the Pierre AugerObservatory and the Telescope Array and the neutrino candidate events fromIceCube and ANTARES

High-energy neutrinos are expected to be produced by the interaction of accelerated particles near the acceleration sites. For this reason, it is interesting to search for correlation in the arrival directions of ultra-high energy cosmic rays (UHECRs) and HE neutrinos. We present here the results of a search for correlations between UHECR events measured by the Pierre Auger Observatory and Telescope Array and high-energy neutrino candidate events from IceCube and ANTARES. We perform a cross-correlation analysis, where the angular separation between the arrival directions of UHECRs and neutrinos is scanned. When comparing the results with the expectations from a null hypothesis contemplating an isotropic distribution of neutrinos or of UHECR we obtain post-trial p-values of the order of $\sim 10^{-2}$.

astro-ph.HE↗
arXiv2017

Towards a medium-scale axion helioscope and haloscope

We discuss the physics case for and the concept of a medium-scale axion helioscope with sensitivities in the axion-photon coupling a few times better than CERN Axion Solar Telescope (CAST). Search for an axion-like particle with these couplings is motivated by several persistent astrophysical anomalies. We present early conceptual design, existing infrastructure, projected sensitivity and timeline of such a helioscope (Troitsk Axion Solar Telescope Experiment, TASTE) to be constructed in the Institute for Nuclear Research, Troitsk, Russia. The proposed instrument may be also used for the search of dark-matter halo axions.

hep-ph↗
arXiv2017

Measurement of Anisotropy and Search for UHECR Sources

Ultra-high energy cosmic rays (UHECRs) are particles, likely protons and/or nuclei, with energies up to $10^{20}$ eV that are observed through the giant air showers they produce in the atmosphere. These particles carry the information on the most extreme phenomena in the Universe. At these energies, even charged particles could be magnetically rigid enough to keep track of, or even point directly to, the original positions of their sources on the sky. The discovery of anisotropy of UHECRs would thus signify opening of an entirely new window onto the Universe. With the construction and operation of the new generation of cosmic ray experiments -- the Pierre Auger Observatory in the Southern hemisphere and the Telescope Array in the Northern one -- the study of these particles, the most energetic ever detected, has experienced a jump in statistics as well as in the data quality, allowing for a much better sensitivity in searching for their sources. In this review, we summarize the searches for anisotropies and the efforts to identify the sources of UHECRs which have been carried out using these new data.

astro-ph.HE↗
arXiv2016

Detection prospects of the Telescope Array hotspot by space observatories

In the present-day cosmic ray data, the strongest indication of anisotropy of the ultrahigh energy cosmic rays is the 20-degree hotspot observed by the Telescope Array with the statistical significance of 3.4\sigma. In this work, we study the possibility of detecting such a spot by space-based all-sky observatories. We show that if the detected luminosity of the hotspot is attributed to a physical effect and not a statistical fluctuation, the KLYPVE and JEM-EUSO experiments would need to collect ~300 events with E>57 EeV in order to detect the hotspot at the 5\sigma\ confidence level with the 68% probability. We also study the dependence of the detection prospects on the hotspot luminosity.

astro-ph.HE↗
arXiv2013

Mass Composition Working Group Report at UHECR-2012

We present a summary of the measurements of mass sensitive parameters at the highest cosmic ray energies done by several experiments. The Xmax distribution as a function of energy has been measured with fluorescence telescopes by the HiRes, TA and Auger experiments and with Cherenkov light detectors by Yakutsk. The or the average mass ( ) has been also inferred using ground detectors, such as muon and water Cherenkov detectors. We discuss the different data analyses elaborated by each collaboration in order to extract the relevant information. Special attention is given to the different approaches used in the analysis of the data measured by fluorescence detectors in order to take into account detector biases. We present a careful analysis of the stability and performance of each analysis. The results of the different experiments will be compared and the discrepancies or agreements will be quantified.

astro-ph.HE↗
arXiv2010

Analysis of large-scale anisotropy of ultra-high energy cosmic rays in HiRes data

Stereo data collected by the HiRes experiment over a six year period are examined for large-scale anisotropy related to the inhomogeneous distribution of matter in the nearby Universe. We consider the generic case of small cosmic-ray deflections and a large number of sources tracing the matter distribution. In this matter tracer model the expected cosmic ray flux depends essentially on a single free parameter, the typical deflection angle theta. We find that the HiRes data with threshold energies of 40 EeV and 57 EeV are incompatible with the matter tracer model at a 95% confidence level unless theta is larger than 10 degrees and are compatible with an isotropic flux. The data set above 10 EeV is compatible with both the matter tracer model and an isotropic flux.

astro-ph.HE↗
arXiv2005

The fate of the zero mode of the five-dimensional kink in the presence of gravity

We investigate what becomes of the translational zero-mode of a five-dimensional domain wall in the presence of gravity, studying the scalar perturbations of a thick gravitating domain wall with AdS asymptotics and a well-defined zero-gravity limit. Our analysis reveals the presence of a wide resonance which can be seen as a remnant of the translational zero-mode present in the domain wall in the absence of gravity and which ensures a continuous change of the physical quantities (such as e.g. static potential between sources) when the Planck mass is sent to infinity. Provided that the thickness of the wall is much smaller than the AdS radius of the space-time, the parameters of this resonance do not depend on details of the domain wall's structure, but solely on the geometry of the space-time.

hep-th↗
arXiv2005

Cosmological attractors in massive gravity

We study Lorentz-violating models of massive gravity which preserve rotations and are invariant under time-dependent shifts of the spatial coordinates. In the linear approximation the Newtonian potential in these models has an extra ``confining'' term proportional to the distance from the source. We argue that during cosmological expansion the Universe may be driven to an attractor point with larger symmetry which includes particular simultaneous dilatations of time and space coordinates. The confining term in the potential vanishes as one approaches the attractor. In the vicinity of the attractor the extra contribution is present in the Friedmann equation which, in a certain range of parameters, gives rise to the cosmic acceleration.

hep-th↗
arXiv2005

TeV signatures of compact UHECR accelerators

We study numerically particle acceleration by the electric field induced near the horizon of a rotating supermassive (M \sim 10^9-10^{10} M_{\odot}) black hole embedded in the magnetic field B. We find that acceleration of protons to energy E > 10^{20} eV is possible only at extreme values of M and B. We also find that the acceleration is very inefficient and is accompanied by a broad band MeV-TeV radiation whose total power exceeds at least by a factor of 1000 the total power emitted in ultra-high energy cosmic rays (UHECR). This implies that if O(10) nearby quasar remnants were sources of proton events with energy E > 10^{20} eV, then each quasar remnant would overshine e.g. the Crab nebula by more than two orders of magnitude in the TeV energy band. Recent TeV observations exclude this possibility. A model in which O(100) sources are situated at 100-1000 Mpc is not ruled out and can be experimentally tested by present TeV gamma-ray telescopes. Such a model can explain the observed UHECR flux at moderate energies E \sim (4-5) 10^{19} eV.

astro-ph↗
arXiv2004

Quasilocalized gravity without asymptotic flatness

We present a toy model of a generic five-dimensional warped geometry in which the 4D graviton is not fully localized on the brane. Studying the tensor sector of metric perturbation around this background, we find that its contribution to the effective gravitational potential is of 4D type (1/r) at the intermediate scales and that at the large scales it becomes 1/r^{1+alpha}, 0<alpha=< 1 being a function of the parameters of the model (alpha=1 corresponds to the asymptotically flat geometry). Large-distance behavior of the potential is therefore not necessarily five-dimensional. Our analysis applies also to the case of quasilocalized massless particles other than graviton.

hep-th↗
arXiv2003

Semiclassical Study of Baryon and Lepton Number Violation in High-Energy Electroweak Collisions

We make use of a semiclassical method for calculating the suppression exponent for topology changing transitions in high-energy electroweak collisions. In the Standard Model these processes are accompanied by violation of baryon and lepton number. By using a suitable computational technique we obtain results for s-wave scattering in a large region of initial data. Our results show that baryon and lepton number violation remains exponentially suppressed up to very high energies of at least 30 sphaleron masses (250 TeV). We also conclude that the known analytic approaches inferred from low energy expansion provide reasonably good approximations up to the sphaleron energy (8 TeV) only.

hep-ph↗