arXiv subjects

Arpine Piloyan

Publications and source records attributed to Arpine Piloyan.

6 recordsLinked to original sources

arXiv2026

A resonance in phonons scattering off a kink in the absence of a Peierls-Nabarro potential

We investigate the interaction of small-amplitude waves called phonons, with an initially static kink in an exceptional discretization of the $\phi^4$ model that is free of the Peierls-Nabarro potential. Phonons are generated by a localized harmonic source and scattered from one side of the kink. By computing the transmission and reflection coefficients over the entire phonon band, we demonstrate that the scattering properties depend strongly on the lattice spacing. In the weak-discreteness regime ($h<1$), the kink is nearly transparent and phonons are transmitted through it over most of the phonon spectrum. In contrast, for strong discreteness ($h>1$), significant reflection emerges even though the corresponding continuum $\phi^4$ kink is reflectionless. We further show that depending on the frequency of the incoming phonons, the kink experiences negative radiation pressure and is accelerated toward the incoming phonons for all lattice spacings considered, and this effect is much stronger for the strong discretness. The frequency dependence of the kink velocity and energy transfer is explained in terms of resonances associated with Doppler-shifted phonon frequencies and extrema of the phonon group velocity. Our results reveal that strong lattice discreteness can qualitatively modify phonon-kink interactions even in systems where the static Peierls-Nabarro potential is absent.

nlin.PS↗

arXiv2022

Advanced Radio Frequency Timing AppaRATus (ARARAT) Technique and Applications

The development of the advanced Radio Frequency Timer of electrons is described. It is based on a helical deflector, which performs circular or elliptical sweeps of keV electrons, by means of 500 MHz radio frequency field. By converting a time distribution of incident electrons to a hit position distribution on a circle or ellipse, this device achieves extremely precise timing. Streak Cameras, based on similar principles, routinely operate in the ps and sub-ps time domain, but have substantial slow readout system. Here, we report a device, where the position sensor, consisting of microchannel plates and a delay-line anode, produces ~ns duration pulses which can be processed by using regular fast electronics. A photon sensor based on this technique, the Radio Frequency Photo-Multiplier Tube (RFPMT), has demonstrated a timing resolution of ~10 ps and a time stability of ~0.5 ps, FWHM. This makes the apparatus highly suited for Time Correlated Single Photon Counting which is widely used in optical microscopy and tomography of biological samples. The first application in lifetime measurements of quantum states of graphene, under construction at the A. I. Alikhanyan National Science Laboratory (AANL), is outlined. This is followed by a description of potential RFPMT applications in time-correlated Diffuse Optical Tomography, time-correlated Stimulated Emission Depletion microscopy, hybrid FRET/STED nanoscopy and Time-of-Flight Positron Emission Tomography.

physics.ins-det↗

arXiv2018

On the Stability of Dark Energy Scalar Field Reconstruction from SNe Ia Data

The current paper addresses the possibility of Dark Energy scalar field potential reconstruction from SNe Ia data and the problems arising during the process. We describe the method and test its limits and features with use of synthetic data, as well as discuss several issues connected to error propagation. We conclude that the chosen smoothing method -- binning of the data -- introduces immense uncertainty amplification which limits the practical application of this method, leaving us with other alternatives. We also address the ``instability of the reconstruction'', an important effect when a false scalar field -- real or phantom -- could be reconstructed if the $\Omega_m$ and $H_0$ parameters are wrongly estimated; a similar effect could be expected in other Dark Energy models as well.

astro-ph.CO↗

arXiv2018

Limits on the Reconstruction of a Single Dark Energy Scalar Field Potential from SNe Ia Data

In this paper we perform a reconstruction of the scalar field potential responsible for cosmic acceleration using SNe Ia data. After describing the method, we test it with real SNe Ia data-Union2.1 and JLA SNe datasets. We demonstrate that with the current data precision level, the full reconstruction is not possible. We discuss the problems which arise during the reconstruction process and the ways to overcome them.

astro-ph.CO↗

arXiv2014

Linear Perturbation constraints on Multi-coupled Dark Energy

The Multi-coupled Dark Energy (McDE) scenario has been recently proposed as a specific example of a cosmological model characterized by a non-standard physics of the dark sector of the universe that nevertheless gives an expansion history which does not significantly differ from the one of the standard $Λ$CDM model. In this work, we present the first constraints on the McDE scenario obtained by comparing the predicted evolution of linear density perturbations with a large compilation of recent data sets for the growth rate $fσ_{8}$, including 6dFGS, LRG, BOSS, WiggleZ and VIPERS. Confirming qualitative expectations, growth rate data provide much tighter bounds on the model parameters as compared to the extremely loose bounds that can be obtained when only the background expansion history is considered. In particular, the $95\%$ confidence level on the coupling strength $|β|$ is reduced from $|β|\leq 83$ (background constraints only) to $|β|\leq 0.88$ (background and linear perturbation constraints). We also investigate how these constraints further improve when using data from future wide-field surveys such as supernova data from LSST and growth rate data from Euclid-type missions. In this case the $95\%$ confidence level on the coupling further reduce to $|β|\leq 0.85$. Such constraints are in any case still consistent with a scalar fifth-force of gravitational strength, and we foresee that tighter bounds might be possibly obtained from the investigation of nonlinear structure formation in McDE cosmologies.[Abridged]

astro-ph.CO↗

arXiv2013

Supernova constraints on Multi-coupled Dark Energy

The persisting consistency of ever more accurate observational data with the predictions of the standard LCDM cosmological model puts severe constraints on possible alternative scenarios, but still does not shed any light on the fundamental nature of the cosmic dark sector.As large deviations from a LCDM cosmology are ruled out by data, the path to detect possible features of alternative models goes necessarily through the definition of cosmological scenarios that leave almost unaffected the background and -- to a lesser extent -- the linear perturbations evolution of the universe. In this context,the Multi-coupled DE (McDE) model was proposed by Baldi 2012 as a particular realization of an interacting Dark Energy field characterized by an effective screening mechanism capable of suppressing the effects of the coupling at the background and linear perturbation level. In the present paper, for the first time, we challenge the McDE scenario through a direct comparison with real data, in particular with the luminosity distance of Type Ia supernovae. By studying the existence and stability conditions of the critical points of the associated background dynamical system, we select only the cosmologically consistent solutions, and confront their background expansion history with data. Confirming previous qualitative results, the McDE scenario appears to be fully consistent with the adopted sample of Type Ia supernovae, even for coupling values corresponding to an associated scalar fifth-force about four orders of magnitude stronger than standard gravity. Our analysis demonstrates the effectiveness of the McDE background screening, and shows some new non-trivial asymptotic solutions for the future evolution of the universe. Our results show how the background expansion history might be highly insensitive to the fundamental nature and to the internal complexity of the dark sector. [Abridged]

astro-ph.CO↗