Results for "S. Buitink"

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The NuMoon experiment: first resultsAug 13 2008The NuMoon project uses the Westerbork Synthesis Radio Telescope to search for short radio pulses from the Moon. These pulses are created when an ultra high energy cosmic ray or neutrino initiates a particle cascade inside the Moon's regolith. The cascade ... More
Cosmic Ray Physics with the LOFAR Radio TelescopeMar 20 2019The LOFAR radio telescope is able to measure the radio emission from cosmic ray induced air showers with hundreds of individual antennas. This allows for precision testing of the emission mechanisms for the radio signal as well as determination of the ... More
Monte Carlo simulations of air showers in atmospheric electric fieldsOct 28 2009The development of cosmic ray air showers can be influenced by atmospheric electric fields. Under fair weather conditions these fields are small, but the strong fields inside thunderstorms can have a significant effect on the electromagnetic component ... More
Simulation of radio emission from air showers in atmospheric electric fieldsFeb 25 2010We study the effect of atmospheric electric fields on the radio pulse emitted by cosmic ray air showers. Under fair weather conditions the dominant part of the radio emission is driven by the geomagnetic field. When the shower charges are accelerated ... More
Calibration of the LOFAR low-band antennas using the Galaxy and a model of the signal chainMar 14 2019The LOw-Frequency ARray (LOFAR) is used to make precise measurements of radio emission from extensive air showers, yielding information about the primary cosmic ray. Interpreting the measured data requires an absolute and frequency-dependent calibration ... More
Search for high-energy neutrinos from dust obscured BlazarsNov 09 2015The recent discovery of high-energy cosmic neutrinos by the IceCube neutrino observatory opens up a new field in physics, the field of neutrino astronomy. Using the IceCube neutrino detector we plan to search for high-energy neutrinos emitted from Active ... More
Energy Spectrum of Fast Second Order Fermi Accelerators as Sources of Ultra-High-Energy Cosmic RaysDec 12 2016Apr 18 2018Stochastic acceleration of cosmic rays in second order Fermi processes is usually considered too slow to reach ultra-high energies, except in specific cases. In this paper we present the energy spectrum obtained from second order Fermi acceleration in ... More
Cosmic-ray energy spectrum and composition up to the ankle - the case for a second Galactic componentMay 10 2016We have carried out a detailed study to understand the observed energy spectrum and composition of cosmic rays with energies up to ~10^18 eV. Our study shows that a single Galactic component with subsequent energy cut-offs in the individual spectra of ... More
Cosmic-ray energy spectrum and composition up to the ankle - the case for a second Galactic componentMay 10 2016Nov 11 2016We have carried out a detailed study to understand the observed energy spectrum and composition of cosmic rays with energies up to ~10^18 eV. Our study shows that a single Galactic component with subsequent energy cut-offs in the individual spectra of ... More
Search for high-energy neutrinos from dust obscured BlazarsNov 09 2015Nov 15 2016The recent discovery of high-energy cosmic neutrinos by the IceCube neutrino observatory opens up a new field in physics, the field of neutrino astronomy. Using the IceCube neutrino detector we plan to search for high-energy neutrinos emitted from Active ... More
Air Shower Measurements with LOFARMar 13 2009Air showers from cosmic rays emit short, intense radio pulses. LOFAR is a new radio telescope, that is being built in the Netherlands and Europe. Designed primarily as a radio interferometer, the core of LOFAR will have a high density of radio antennas, ... More
A new limit on the Ultra-High-Energy Cosmic-Ray flux with the Westerbork Synthesis Radio TelescopeOct 28 2010A particle cascade (shower) in a dielectric, for example as initiated by an ultra-high energy cosmic ray, will have an excess of electrons which will emit coherent \v{C}erenkov radiation, known as the Askaryan effect. In this work we study the case in ... More
Obscured flat spectrum radio AGN as sources of high-energy neutrinosJul 29 2016Active Galactic Nuclei (AGN) are believed to be one of the main source candidates for the high-energy (TeV-PeV) cosmic neutrino flux recently discovered by the IceCube neutrino observatory. Nevertheless, several correlation studies between AGN and the ... More
Improved flux limits for neutrinos with energies above 10$^{22}$ eV from observations with the Westerbork Synthesis Radio TelescopeOct 25 2009Particle cascades initiated by ultra-high energy (UHE) neutrinos in the lunar regolith will emit an electromagnetic pulse with a time duration of the order of nano seconds through a process known as the Askaryan effect. It has been shown that in an observing ... More
Obscured flat spectrum radio AGN as sources of high-energy neutrinosJul 29 2016Oct 31 2016Active Galactic Nuclei (AGN) are believed to be one of the main source candidates for the high-energy (TeV-PeV) cosmic neutrino flux recently discovered by the IceCube neutrino observatory. Nevertheless, several correlation studies between AGN and the ... More
Constraints on the flux of Ultra-High Energy neutrinos from WSRT observationsApr 02 2010Ultra-high energy (UHE) neutrinos and cosmic rays initiate particle cascades underneath the Moon's surface. These cascades have a negative charge excess and radiate Cherenkov radio emission in a process known as the Askaryan effect. The optimal frequency ... More
Status report of the NuMoon experimentOct 19 2008We show that at wavelengths comparable to the length of the shower produced by an Ultra-High Energy cosmic ray or neutrino, radio signals are an extremely efficient way to detect these particles. First results are presented of an analysis of 20 hours ... More
Precision measurements of cosmic ray air showers with the SKAAug 22 2014Jan 08 2015Supplemented with suitable buffering techniques, the low-frequency part of the SKA can be used as an ultra-precise detector for cosmic-ray air showers at very high energies. This would enable a wealth of scientific applications: the physics of the transition ... More
Initial simulation study on high-precision radio measurements of the depth of shower maximum with SKA1-lowFeb 01 2017As LOFAR has shown, using a dense array of radio antennas for detecting extensive air showers initiated by cosmic rays in the Earth's atmosphere makes it possible to measure the depth of shower maximum for individual showers with a statistical uncertainty ... More
The effect of the atmospheric refractive index on the radio signal of extensive air showersJan 25 2017For the interpretation of measurements of radio emission from extensive air showers, an important systematic uncertainty arises from natural variations of the atmospheric refractive index $n$. At a given altitude, the refractivity $N=10^6\, (n-1)$ can ... More
Realtime processing of LOFAR data for the detection of nano-second pulses from the MoonDec 20 2016The low flux of the ultra-high energy cosmic rays (UHECR) at the highest energies provides a challenge to answer the long standing question about their origin and nature. Even lower fluxes of neutrinos with energies above $10^{22}$ eV are predicted in ... More
Measurement of the cosmic-ray energy spectrum above $10^{16}$ eV with the LOFAR Radboud Air Shower ArrayJun 30 2015Jul 01 2015The energy reconstruction of extensive air showers measured with the LOFAR Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle detector array located in the center of the LOFAR radio telescope in the Netherlands. The aim of this ... More
Search for Cosmic Particles with the Moon and LOFARSep 21 2016The low flux of the ultra-high energy cosmic rays (UHECR) at the highest energies provides a challenge to answer the long standing question about their origin and nature. A significant increase in the number of detected UHECR is expected to be achieved ... More
LORA: A scintillator array for LOFAR to measure extensive air showersAug 19 2014The measurement of the radio emission from extensive air showers, induced by high-energy cosmic rays is one of the key science projects of the LOFAR radio telescope. The LOfar Radboud air shower Array (LORA) has been installed in the core of LOFAR in ... More
Polarized radio emission from extensive air showers measured with LOFARJun 05 2014Sep 09 2014We present LOFAR measurements of radio emission from extensive air showers. We find that this emission is strongly polarized, with a median degree of polarization of nearly $99\%$, and that the angle between the polarization direction of the electric ... More
A method for high precision reconstruction of air shower Xmax using two-dimensional radio intensity profilesAug 29 2014Sep 01 2014The mass composition of cosmic rays contains important clues about their origin. Accurate measurements are needed to resolve long-standing issues such as the transition from Galactic to extragalactic origin, and the nature of the cutoff observed at the ... More
Status of the Lunar Detection Mode for Cosmic Particles of LOFARMar 20 2019Cosmic particles hitting Earth's moon produce radio emission via the Askaryan effect. If the resulting radio ns-pulse can be detected by radio telescopes, this technique potentially increases the available collective area for ZeV scale particles by several ... More
The lunar Askaryan technique: a technical roadmapSep 17 2015The lunar Askaryan technique, which involves searching for Askaryan radio pulses from particle cascades in the outer layers of the Moon, is a method for using the lunar surface as an extremely large detector of ultra-high-energy particles. The high time ... More
Amplified radio emission from cosmic ray air showers in thunderstormsFeb 16 2007Feb 26 2007Cosmic ray air showers produce radio emission, consisting in large part of geosynchrotron emission. Since the radiation mechanism is based on particle acceleration, the atmospheric electric field can play an important role. Especially inside thunderclouds ... More
Timing calibration and spectral cleaning of LOFAR time series dataMar 28 2016We describe a method for spectral cleaning and timing calibration of short voltage time series data from individual radio interferometer receivers. It makes use of the phase differences in Fast Fourier Transform (FFT) spectra across antenna pairs. For ... More
The radio emission pattern of air showers as measured with LOFAR - a tool for the reconstruction of the energy and the shower maximumNov 28 2014Apr 13 2015The pattern of the radio emission of air showers is finely sampled with the Low-Frequency ARray (LOFAR). A set of 382 measured air showers is used to test a fast, analytic parameterization of the distribution of pulse powers. Using this parameterization ... More
Lunar detection of ultra-high-energy cosmic rays and neutrinos with the Square Kilometre ArrayAug 26 2014Dec 19 2014The origin of the most energetic particles in nature, the ultra-high-energy (UHE) cosmic rays, is still a mystery. Only the most energetic of these have sufficiently small angular deflections to be used for directional studies, and their flux is so low ... More
High-precision measurements of extensive air showers with the SKAAug 14 2015As of 2023, the Square Kilometre Array will constitute the world's largest radio telescope, offering unprecedented capabilities for a diverse science programme in radio astronomy. At the same time, the SKA will be ideally suited to detect extensive air ... More
Influence of Atmospheric Electric Fields on the Radio Emission from Extensive Air ShowersNov 10 2015The atmospheric electric fields in thunderclouds have been shown to significantly modify the intensity and polarization patterns of the radio footprint of cosmic-ray-induced extensive air showers. Simulations indicated a very non-linear dependence of ... More
Measurement of the circular polarization in radio emission from extensive air showers confirms emission mechanismsNov 02 2016Nov 19 2016We report here on a novel analysis of the complete set of four Stokes parameters that uniquely determine the linear and/or circular polarization of the radio signal for an extensive air shower. The observed dependency of the circular polarization on azimuth ... More
Measurement of the circular polarization in radio emission from extensive air showers confirms emission mechanismsNov 02 2016We report here on a novel analysis of the complete set of four Stokes parameters that uniquely determine the linear and/or circular polarization of the radio signal for an extensive air shower. The observed dependency of the circular polarization on azimuth ... More
Thunderstorm electric fields probed by extensive air showers through their polarized radio emissionMar 14 2017Mar 20 2017We observe a large fraction of circular polarization in radio emission from extensive air showers recorded during thunderstorms, much higher than in the emission from air showers measured during fair-weather circumstances. We show that the circular polarization ... More
A parameterization for the radio emission of air showers as predicted by CoREAS simulations and applied to LOFAR measurementsFeb 12 2014Jun 19 2014Measuring radio emission from air showers provides excellent opportunities to directly measure all air shower properties, including the shower development. To exploit this in large-scale experiments, a simple and analytic parameterization of the distribution ... More
IceTop: The surface component of IceCubeJul 26 2012Jul 27 2012IceTop, the surface component of the IceCube Neutrino Observatory at the South Pole, is an air shower array with an area of 1 km2. The detector allows a detailed exploration of the mass composition of primary cosmic rays in the energy range from about ... More
Lateral Distribution of Muons in IceCube Cosmic Ray EventsAug 14 2012Dec 12 2012In cosmic ray air showers, the muon lateral separation from the center of the shower is a measure of the transverse momentum that the muon parent acquired in the cosmic ray interaction. IceCube has observed cosmic ray interactions that produce muons laterally ... More
Searches for high-energy neutrino emission in the Galaxy with the combined IceCube-AMANDA detectorOct 11 2012Jan 09 2013We report on searches for neutrino sources at energies above 200 GeV in the Northern sky of the galactic plane, using the data collected by the South Pole neutrino telescopes IceCube and AMANDA. The galactic region considered here includes the Local Arm ... More
The cosmic-ray air-shower signal in Askaryan radio detectorsMar 10 2015Nov 25 2015We discuss the radio emission from high-energy cosmic-ray induced air showers hitting Earth's surface before the cascade has died out in the atmosphere. The induced emission gives rise to a radio signal which should be detectable in the currently operating ... More
Livetime and sensitivity of the ARIANNA Hexagonal Radio ArraySep 01 2015The ARIANNA collaboration completed the installation of the hexagonal radio array (HRA) in December 2014, serving as a pilot program for a planned high energy neutrino telescope located about 110 km south of McMurdo Station on the Ross Ice Shelf near ... More
Performance of the ARIANNA Hexagonal Radio ArraySep 01 2015Installation of the ARIANNA Hexagonal Radio Array (HRA) on the Ross Ice Shelf of Antarctica has been completed. This detector serves as a pilot program to the ARIANNA neutrino telescope, which aims to measure the diffuse flux of very high energy neutrinos ... More
A First Search for Cosmogenic Neutrinos with the ARIANNA Hexagonal Radio ArrayOct 27 2014Sep 01 2015The ARIANNA experiment seeks to observe the diffuse flux of neutrinos in the 10^8 - 10^10 GeV energy range using a grid of radio detectors at the surface of the Ross Ice Shelf of Antarctica. The detector measures the coherent Cherenkov radiation produced ... More
Prospects of Probing the Radio Emission of Lunar UHECRv EventsAug 07 2018Radio detection of Ultra High Energetic Cosmic Rays and Neutrinos (UHECRv) which hit the Moon has been investigated in recent years. In preparation for near-future lunar science missions, we discuss technical requirements for radio experiments onboard ... More
Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFARNov 25 2014Measuring radio emission from air showers offers a novel way to determine properties of the primary cosmic rays such as their mass and energy. Theory predicts that relativistic time compression effects lead to a ring of amplified emission which starts ... More
Lateral Distribution of the Radio Signal in Extensive Air Showers Measured with LOPESOct 26 2009The antenna array LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from Extensive Air Showers. The coincident measurements allow us to reconstruct ... More
Muon Counting using Silicon Photomultipliers in the AMIGA detector of the Pierre Auger ObservatoryMar 17 2017Oct 04 2017AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory designed to extend its energy range of detection and to directly measure the muon content of the cosmic ray primary particle showers. The array will be formed ... More
Ultrahigh-energy neutrino follow-up of Gravitational Wave events GW150914 and GW151226 with the Pierre Auger ObservatoryAug 26 2016Jan 13 2017On September 14, 2015 the Advanced LIGO detectors observed their first gravitational-wave (GW) transient GW150914. This was followed by a second GW event observed on December 26, 2015. Both events were inferred to have arisen from the merger of black ... More
Indication of anisotropy in arrival directions of ultra-high-energy cosmic rays through comparison to the flux pattern of extragalactic gamma-ray sourcesJan 18 2018Feb 06 2018A new analysis of the dataset from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. ... More
Observation of a Large-scale Anisotropy in the Arrival Directions of Cosmic Rays above $8 \times 10^{18}$ eVSep 21 2017Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. Using $3 \times 10^4$ cosmic rays above $8 \times 10^{18}$ ... More
Multi-Messenger Physics with the Pierre Auger ObservatoryApr 26 2019An overview of the multi-messenger capabilities of the Pierre Auger Observatory is presented. The techniques and performance of searching for Ultra-High Energy neutrinos, photons and neutrons are described. Some of the most relevant results are reviewed, ... More
Calibration of the Logarithmic-Periodic Dipole Antenna (LPDA) Radio Stations at the Pierre Auger Observatory using an OctocopterFeb 05 2017Jun 13 2018An in-situ calibration of a logarithmic periodic dipole antenna with a frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of a radio station system used for detection of cosmic ray induced air showers at the Engineering Radio ... More
Search for photons with energies above 10$^{18}$ eV using the hybrid detector of the Pierre Auger ObservatoryDec 05 2016Apr 07 2017A search for ultra-high energy photons with energies above 1 EeV is performed using nine years of data collected by the Pierre Auger Observatory in hybrid operation mode. An unprecedented separation power between photon and hadron primaries is achieved ... More
Spectral Calibration of the Fluorescence Telescopes of the Pierre Auger ObservatorySep 05 2017Oct 02 2017We present a novel method to measure precisely the relative spectral response of the fluorescence telescopes of the Pierre Auger Observatory. We used a portable light source based on a xenon flasher and a monochromator to measure the relative spectral ... More
Search for ultrarelativistic magnetic monopoles with the Pierre Auger ObservatorySep 14 2016Oct 03 2016We present a search for ultra-relativistic magnetic monopoles with the Pierre Auger Observatory. Such particles, possibly a relic of phase transitions in the early universe, would deposit a large amount of energy along their path through the atmosphere, ... More
A targeted search for point sources of EeV photons with the Pierre Auger ObservatoryDec 13 2016Mar 21 2017Simultaneous measurements of air showers with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for EeV photon point sources. Several Galactic and extragalactic candidate objects are grouped in classes to ... More
Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger ObservatoryNov 21 2016Jun 20 2017We report a multi-resolution search for anisotropies in the arrival directions of cosmic rays detected at the Pierre Auger Observatory with local zenith angles up to $80^\circ$ and energies in excess of 4 EeV ($4 \times 10^{18}$ eV). This search is conducted ... More
On noise treatment in radio measurements of cosmic ray air showersSep 17 2010Precise measurements of the radio emission by cosmic ray air showers require an adequate treatment of noise. Unlike to usual experiments in particle physics, where noise always adds to the signal, radio noise can in principle decrease or increase the ... More
Data-driven estimation of the invisible energy of cosmic ray showers with the Pierre Auger ObservatoryJan 23 2019Feb 04 2019The determination of the primary energy of extensive air showers using the fluorescence detection technique requires an estimation of the energy carried away by particles that do not deposit all their energy in the atmosphere. This estimation is typically ... More
Thunderstorm Observations by Air-Shower Radio Antenna ArraysMar 28 2013Relativistic, charged particles present in extensive air showers lead to a coherent emission of radio pulses which are measured to identify the shower initiating high-energy cosmic rays. Especially during thunderstorms, there are additional strong electric ... More
Nanosecond-level time synchronization of autonomous radio detector stations for extensive air showersDec 07 2015Feb 15 2016To exploit the full potential of radio measurements of cosmic-ray air showers at MHz frequencies, a detector timing synchronization within 1 ns is needed. Large distributed radio detector arrays such as the Auger Engineering Radio Array (AERA) rely on ... More
Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger ObservatoryOct 26 2016Oct 31 2016Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators. Here we introduce a new method to test hadronic interaction models without relying on the absolute energy calibration, and apply it to events ... More
Prototype muon detectors for the AMIGA component of the Pierre Auger ObservatoryMay 05 2016May 12 2016Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory to extend its range of detection and to directly measure the muon content of the particle showers. It consists of an infill of surface water-Cherenkov detectors ... More
Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger ObservatoryApr 04 2016Apr 13 2016The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects ... More
NNLO classical solution for Lipatov's effective action for reggeized gluonsFeb 15 2018Mar 19 2018We consider the formalism of small-x effective action for reggeized gluons, Gribov (Sov Phys JETP 26:414, 1968), Lipatov (Nucl Phys B 452:369, 1995; Phys Rep 286:131, 1997; Subnucl Ser 49:131, 2013, Int J Mod Phys Conf Ser 39:1560082, 2015; Int J Mod ... More
Band insulator to Mott insulator transition in a bilayer Hubbard modelMar 27 2007The ground state phase diagram of the half-filled repulsive Hubbard model in a bilayer is investigated using cluster dynamical mean field theory. For weak to intermediate values of Coulomb repulsion $U$, the system undergoes a transition from a Mott insulating ... More
Detecting cosmic rays with the LOFAR radio telescopeNov 06 2013The low frequency array (LOFAR), is the first radio telescope designed with the capability to measure radio emission from cosmic-ray induced air showers in parallel with interferometric observations. In the first $\sim 2\,\mathrm{years}$ of observing, ... More
Searching for Neutrino Radio Flashes from the Moon with LOFARJan 22 2013Ultra-high-energy neutrinos and cosmic rays produce short radio flashes through the Askaryan effect when they impact on the Moon. Earthbound radio telescopes can search the Lunar surface for these signals. A new generation of low- frequency, digital radio ... More
Searches for Large-Scale Anisotropy in the Arrival Directions of Cosmic Rays Detected above Energy of $10^{19}$ eV at the Pierre Auger Observatory and the Telescope ArraySep 10 2014Spherical harmonic moments are well-suited for capturing anisotropy at any scale in the flux of cosmic rays. An unambiguous measurement of the full set of spherical harmonic coefficients requires full-sky coverage. This can be achieved by combining data ... More
Detecting Radio Emission from Air Showers with LOFARApr 03 2013LOFAR (the Low Frequency Array) is the largest radio telescope in the world for observing low frequency radio emission from 10 to 240 MHz. In addition to its use as an interferometric array, LOFAR is now routinely used to detect cosmic ray induced air ... More
Characterization of almost maximally almost-periodic groupsMar 08 2009Let $G$ be an abelian group. We prove that a group $G$ admits a Hausdorff group topology $\tau$ such that the von Neumann radical $\mathbf{n}(G, \tau)$ of $(G, \tau)$ is non-trivial and finite iff $G$ has a non-trivial finite subgroup. If $G$ is a topological ... More
Some families of graphs with no nonzero real domination rootsMar 12 2015Let G be a simple graph of order n. The domination polynomial is the generating polynomial for the number of dominating sets of G of each cardinality. A root of this polynomial is called a domination root of G. Obviously 0 is a domination root of every ... More
Domination polynomials of k-tree related graphsJul 22 2014Let $G$ be a simple graph of order $n$. The domination polynomial of $G$ is the polynomial $D(G, x)=\sum_{i=\gamma(G)}^{n} d(G,i) x^{i}$, where $d(G,i)$ is the number of dominating sets of $G$ of size $i$ and $\gamma(G)$ is the domination number of $G$. ... More
A scaling law for the cosmological constant from a stochastic model for cosmic structuresNov 30 2008May 12 2009A set of scaling laws, based on the stochastic motions of the granular components of astronomical systems, is applied to a cosmological model with a positive cosmological constant. It follows that the mass of the dominant particle in the observable universe ... More
Fractal large-scale structure from a stochastic scaling law modelMar 27 2009A stochastic model relating the parameters of astrophysical structures to the parameters of their granular components is applied to the formation of hierarchical, large-scale structures from galaxies assumed as point-like objects. If the density profile ... More
Interval decomposition lattices are balancedJun 24 2013Jun 27 2013Intervals in binary or n-ary relations or other discrete structures generalize the concept of interval in a linearly ordered set. Join-irreducible partitions into intervals are characterized in the lattice of all interval decompositions of a set, in a ... More
Explicit computation of the electrostatic energy for an elliptical charged discJan 06 2014This letter describes a method for obtaining an explicit expression for the electrostatic energy of a charged elliptical infinitely thin disc. The charge distribution is assumed to be polynomial. Such explicit values for this energy are fundamental for ... More
Quotient Equations and Integrals of Motion for Vector Massless FieldDec 14 2002In this article a group-theoretical aspect of the method of dimensional reduction is presented. Then, on the base of symmetry analysis of an anisotropic space geometrical description of dimensional reduction of equations for vector massless field is given. ... More
Soft-wall modelling of meson spectraApr 11 2016Apr 14 2016The holographic methods inspired by the gauge/gravity correspondence from string theory have been actively applied to the hadron spectroscopy in the last eleven years. Within the phenomenological bottom-up approach, the linear Regge-like trajectories ... More
Veneziano like amplitude as a test for AdS/QCD modelsNov 24 2011The high energy asymptotics of QCD correlation functions is often used as a test for bottom-up holographic models. Since QCD is not strongly coupled in the ultraviolet domain, such a test may look questionable. We propose that the sum over resonance poles ... More
A five-dimensional ansatz for the Veneziano amplitudeFeb 14 2011Jul 11 2012A hypothesis is put forward that in the case of low-energy QCD, the holographic prescription for calculating the correlation functions may lead to the dual scattering amplitudes of Veneziano type at zero momentum transfer if the non-conformality is properly ... More
Axial coupling from matching constituent quark model to QCDMay 19 2008The axial-vector coupling $g_A$ of a constituent quark is estimated from matching the constituent quark model to the operator product expansion in QCD in the limit of large number of colours under some assumptions. The obtained relation is $g_A\simeq\sqrt{7/11}\approx0.80$, ... More
A five-dimensional effective model for excited light mesonsJul 28 2010In the usual holographic approach to QCD, the meson spectrum is generated due to a non-trivial 5-dimensional background. We propose an alternative 5-dimensional scenario in which the spectrum emerges due to coupling to a scalar field whose condensation ... More
Hydrogen like classification for light nonstrange mesonsSep 27 2007Sep 09 2008The recent experimental results on the spectrum of highly excited light nonstrange mesons are known to reveal a high degree of degeneracy among different groups of states. We revise some suggestions about the nature of the phenomenon and put the relevant ... More
Light meson spectrum and classical symmetries of QCDJun 29 2006Jul 24 2006Modern spectroscopic data on light non-strange meson spectrum is analyzed. It is argued that the observed regularities of experimental spectrum for highly excited states favour a partial restoration of all approximate classical symmetries of QCD Lagrangian ... More
Relation between quark and gluon condensates from QCD sum rulesMar 22 2006A new relation between $\rho$-meson mass, weak $\pi$-meson decay constant, quark and gluon condensates is derived from the QCD sum rules. As a byproduct an explanation for the dominance of $\rho\rho$-decay for the $f_0(1370)$-meson is proposed.
Finite time analysis based on Sum of Squares Technique: Applied to the super-twisting second order sliding mode controlJun 08 2015Finite time analysis of the continuous system is investigated through both stability and stabilization based on Sum of squares programming. A systematic approach is proposed to construct Lyapunov function and Control Lyapunov function for this objective. ... More
Empirical Emission Functions for LPM Suppression of Photon Emission from Quark-Gluon PlasmaNov 06 2002The LPM suppression of photon emission rates from the quark gluon plasma have been studied at different physical conditions of the plasma given by temperature and chemical potentials.The integral equation for the transverse vector function (f(p_t)) consisting ... More
On the Variational method for LPM Suppression of Photon Emission from Quark-Gluon PlasmaAug 12 2002The photon emission rates from the quark gluon plasma have been studied considering LPM suppression effects. The integral equation for the transverse vector function (f(p)) that consists of multiple scattering effects has been solved using self-consistent ... More
Straight homotopy invariantsMay 02 2014May 29 2014Let $X$ and $Y$ be spaces and $M$ be an abelian group. A homotopy invariant $f\colon [X,Y]\to M$ is called straight if there exists a homomorphism $F\colon L(X,Y)\to M$ such that $f([a])=F(\langle a\rangle)$ for all $a\in C(X,Y)$. Here $\langle a\rangle\colon\langle ... More
Commutative algebras and representations of the category of finite setsNov 29 2010Apr 03 2011We prove that two finite-dimensional commutative algebras over an algebraically closed field are isomorphic if and only if they give rise to isomorphic representations of the category of finite sets and surjective maps.
Order of a homotopy invariant in the stable caseAug 31 2009Let X and Y be CW-complexes, U be an abelian group, and f:[X,Y]->U be a map (a homotopy invariant). We say that f has order at most r if the characteristic function of the r'th Cartesian power of the graph of a continuous map a:X->Y Z-linearly determines ... More
CP-violation and $ππ$-interaction in the radiative decays of $K_L$ and $K_S$May 15 2002May 31 2002The phases of terms of amplitude that arise from the $\pi\pi$ interaction are obtained by using a simple realistic model of $\pi\pi$ interaction via virtual $\rho$-meson, instead of the ChPT. It is shown that the standard ChPT approach cannot reproduce ... More
General relativistic MHD simulations of monopole magnetospheres of black holesFeb 18 2004Mar 10 2004In this paper we report the results of the first ever time-dependent general relativistic magnetohydrodynamic simulations of the magnetically dominated monopole magnetospheres of black holes. It is found that the numerical solution evolves towards a stable ... More
Electrodynamics of black hole magnetospheresFeb 17 2004Apr 02 2004Numerical simulations combined with simple analytical arguments are used to reach a number of important conclusions on the nature of the Blandford-Znajek mechanism. We show that, just like in the Penrose mechanism and in the MHD models of Punsly and Coroniti, ... More
Supersymmetric Mechanics in SuperspaceFeb 20 2006These Lectures have been given at Laboratori Nazionali di Frascati in the month of March, 2005. The main idea was to provide our young collegues, who joined us in our attempts to understand the structure of $N$-extended supersymmetric one-dimensional ... More