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D. Gorbunov

Publications and source records attributed to D. Gorbunov.

At least 55 records · Page 3Linked to original sources
arXiv2016

Dark matter component decaying after recombination: lensing constraints with Planck data

It has been recently suggested~\cite{Berezhiani:2015yta} that emerging tension between cosmological parameter values derived in high-redshift (CMB anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can be reconciled in a model which contains subdominant fraction of dark matter decaying after recombination. We check the model against the CMB Planck data. We find that lensing of the CMB anisotropies by the large-scale structure gives strong extra constraints on this model, limiting the fraction as $F<8\%$ at 2\,$σ$ confidence level. However, investigating the combined data set of CMB and conflicting low-$z$ measurements, we obtain that the model with $F\approx2\!-\!5$\% exhibits better fit (by 1.5-3\,$σ$ depending on the lensing priors) compared to that of the concordance $Λ$CDM cosmological model.

astro-ph.CO↗
arXiv2015

Decaying light particles in the SHiP experiment. II. Signal rate estimates for light neutralinos

Considering the supersymmetric models with light neutralino and R-parity violation, we perform estimates of the signal rate expected at the recently proposed fixed target SHiP experiment exploiting CERN SPS beam of 400 GeV protons. We extend the existing studies by introducing new production channels (in particular through the beauty mesons) and decay modes. We also constrain model parameter space from analysis of negative results of the CHARM experiment.

hep-ph↗
arXiv2015

A facility to Search for Hidden Particles (SHiP) at the CERN SPS

A new general purpose fixed target facility is proposed at the CERN SPS accelerator which is aimed at exploring the domain of hidden particles and make measurements with tau neutrinos. Hidden particles are predicted by a large number of models beyond the Standard Model. The high intensity of the SPS 400~GeV beam allows probing a wide variety of models containing light long-lived exotic particles with masses below ${\cal O}$(10)~GeV/c$^2$, including very weakly interacting low-energy SUSY states. The experimental programme of the proposed facility is capable of being extended in the future, e.g. to include direct searches for Dark Matter and Lepton Flavour Violation.

physics.ins-det↗
arXiv2015

Relic Gravity Waves and 7 keV Dark Matter from a GeV scale inflaton

We study the mechanism of generation of 7 keV sterile neutrino Dark Matter (DM) in the model with light inflaton $χ$, which serves as a messenger of scale invariance breaking. In this model the inflaton, in addition to providing reheating to the Standard Model (SM) particles, decays directly into sterile neutrinos. The latter are responsible for the active neutrino oscillations via seesaw type I like formula. While the two sterile neutrinos may also produce the lepton asymmetry in the primordial plasma and hence explain the baryon asymmetry of the Universe, the third one being the lightest may be of 7 keV and serve as DM. For this mechanism to work, the mass of the inflaton is bound to be light (0.1-1 GeV) and uniquely determines its properties, which allows to test the model. For particle physics experiments these are: inflaton lifetime ($10^{-5}-10^{-12}$ s), partial decay width of B-meson to kaon and inflaton ($10^{-6}-10^{-4}$) and inflaton branching ratios into light SM particles like it would be for the SM Higgs boson of the same mass. For cosmological experiments these are: spectral index of scalar perturbations ($n_s\simeq0.957-0.967$), and amount of tensor perturbations produced at inflation (tensor-to-scalar ratio $r\simeq0.15-0.005$).

hep-ph↗
arXiv2013

Proposal to Search for Heavy Neutral Leptons at the SPS

A new fixed-target experiment at the CERN SPS accelerator is proposed that will use decays of charm mesons to search for Heavy Neutral Leptons (HNLs), which are right-handed partners of the Standard Model neutrinos. The existence of such particles is strongly motivated by theory, as they can simultaneously explain the baryon asymmetry of the Universe, account for the pattern of neutrino masses and oscillations and provide a Dark Matter candidate. Cosmological constraints on the properties of HNLs now indicate that the majority of the interesting parameter space for such particles was beyond the reach of the previous searches at the PS191, BEBC, CHARM, CCFR and NuTeV experiments. For HNLs with mass below 2 GeV, the proposed experiment will improve on the sensitivity of previous searches by four orders of magnitude and will cover a major fraction of the parameter space favoured by theoretical models. The experiment requires a 400 GeV proton beam from the SPS with a total of 2x10^20 protons on target, achievable within five years of data taking. The proposed detector will reconstruct exclusive HNL decays and measure the HNL mass. The apparatus is based on existing technologies and consists of a target, a hadron absorber, a muon shield, a decay volume and two magnetic spectrometers, each of which has a 0.5 Tm magnet, a calorimeter and a muon detector. The detector has a total length of about 100 m with a 5 m diameter. The complete experimental set-up could be accommodated in CERN's North Area. The discovery of a HNL would have a great impact on our understanding of nature and open a new area for future research.

hep-ex↗
arXiv2013

Antibaryonic dark matter

Assuming existence of (very) heavy fourth generation of quarks and antiquarks we argue that antibaryon composed of the three heavy antiquarks can be light, stable and invisible, hence a good candidate for the Dark matter particle. Such opportunity allows to keep the baryon number conservation for the generation of the visible baryon asymmetry. The dark matter particles traveling through the ordinary matter will annihilate with nucleons inducing proton(neutron)-decay-like events with ~5GeV energy release in outcoming particles.

hep-ph↗
arXiv2013

Light inflaton after LHC8 and WMAP9 results

We update the allowed parameter space of the simple chaotic inflationary model with quartic potential and light inflaton [Bezrukov,Gorbunov'2009] taking into account recent results from cosmology (CMB observations from SPT, ACT and WMAP) and from particle physics (LHC hints of the SM Higgs boson). The non-minimal (yet small) coupling to gravity of the inflaton becomes essential to fit the observational data. The inflaton has mass above 300 MeV and can be searched for at B-factories in B-meson two-body decays to kaon and inflaton. The inflaton lifetime depends on the model parameters, resulting in various inflaton signatures: either a missing energy, or a displaced vertex from the B-meson decay position, or a resonance in the Dalitz plot of a three particle decay. We also discuss the implementation of the inflaton model to the nuMSM, where the inflaton can be responsible for production of the dark matter sterile neutrino in the early Universe.

hep-ph↗
arXiv2012

The surface detector array of the Telescope Array experiment

The Telescope Array (TA) experiment, located in the western desert of Utah,USA, is designed for observation of extensive air showers from extremely high energy cosmic rays. The experiment has a surface detector array surrounded by three fluorescence detectors to enable simultaneous detection of shower particles at ground level and fluorescence photons along the shower track. The TA surface detectors and fluorescence detectors started full hybrid observation in March, 2008. In this article we describe the design and technical features of the TA surface detector.

astro-ph.IM↗
arXiv2012

The Energy Spectrum of Telescope Array's Middle Drum Detector and the Direct Comparison to the High Resolution Fly's Eye Experiment

The Telescope Array's Middle Drum fluorescence detector was instrumented with telescopes refurbished from the High Resolution Fly's Eye's HiRes-1 site. The data observed by Middle Drum in monocular mode was analyzed via the HiRes-1 profile-constrained geometry reconstruction technique and utilized the same calibration techniques enabling a direct comparison of the energy spectra and energy scales between the two experiments. The spectrum measured using the Middle Drum telescopes is based on a three-year exposure collected between December 16, 2007 and December 16, 2010. The calculated difference between the spectrum of the Middle Drum observations and the published spectrum obtained by the data collected by the HiRes-1 site allows the HiRes-1 energy scale to be transferred to Middle Drum. The HiRes energy scale is applied to the entire Telescope Array by making a comparison between Middle Drum monocular events and hybrid events that triggered both Middle Drum and the Telescope Array's scintillator Ground Array.

astro-ph.IM↗
arXiv2011

New air fluorescence detectors employed in the Telescope Array experiment

Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been observing ultra high energy cosmic rays to understand their origins. The experiment involves a surface detector (SD) array and three fluorescence detector (FD) stations. FD stations, installed surrounding the SD array, measure the air fluorescence light emitted from extensive air showers (EASs) for precise determination of their energies and species. The detectors employed at one of the three FD stations were relocated from the High Resolution Fly's Eye experiment. At the other two stations, newly designed detectors were constructed for the TA experiment. An FD consists of a primary mirror and a camera equipped with photomultiplier tubes. To obtain the EAS parameters with high accuracies, understanding the FD optical characteristics is important. In this paper, we report the characteristics and installation of new FDs and the performances of the FD components. The results of the monitored mirror reflectance during the observation time are also described in this report.

astro-ph.IM↗
arXiv2011

The 2010 Interim Report of the Long-Baseline Neutrino Experiment Collaboration Physics Working Groups

In early 2010, the Long-Baseline Neutrino Experiment (LBNE) science collaboration initiated a study to investigate the physics potential of the experiment with a broad set of different beam, near- and far-detector configurations. Nine initial topics were identified as scientific areas that motivate construction of a long-baseline neutrino experiment with a very large far detector. We summarize the scientific justification for each topic and the estimated performance for a set of far detector reference configurations. We report also on a study of optimized beam parameters and the physics capability of proposed Near Detector configurations. This document was presented to the collaboration in fall 2010 and updated with minor modifications in early 2011.

hep-ex↗
arXiv2011

Late and early time phenomenology of Higgs-dependent cutoff

The analysis of theories with non-minimal coupling of Higgs field to gravity revealed that they enter into strong coupling regime above certain Higgs-dependent cutoff, which may be considerably below the Planck scale. Assuming that the effective theory, complementing the Standard Model or its minimal extension--the nuMSM--contains a set of higher dimensional operators suppressed by the Higgs-dependent cutoff, we analyse the reheating of the Universe after the Higgs inflation. We show that extra terms do not spoil the Higgs inflation, but can lead to baryogenesis and to warm sterile neutrino dark matter production at the reheating stage of the Universe expansion. They can also result in neutrino mass generation and proton decay.

hep-ph↗
arXiv2010

Light inflaton Hunter's Guide

We study the phenomenology of a realistic version of the chaotic inflationary model, which can be fully and directly explored in particle physics experiments. The inflaton mixes with the Standard Model Higgs boson via the scalar potential, and no additional scales above the electroweak scale are present in the model. The inflaton-to-Higgs coupling is responsible for both reheating in the Early Universe and the inflaton production in particle collisions. We find the allowed range of the light inflaton mass, 270 MeV<~m_chi<~1.8 GeV, and discuss the ways to find the inflaton. The most promising are two-body kaon and B-meson decays with branching ratios of orders 10^{-9} and 10^{-6}, respectively. The inflaton is unstable with the lifetime 10^{-9}--10^{-10} s. The inflaton decays can be searched for in a beam-target experiment, where, depending on the inflaton mass, from several billions to several tenths of millions inflatons can be produced per year with modern high-intensity beams.

hep-ph↗
arXiv2009

On initial conditions for the Hot Big Bang

We analyse the process of reheating the Universe in the electroweak theory where the Higgs field plays a role of the inflaton. We estimate the maximal temperature of the Universe and fix the initial conditions for radiation-dominated phase of the Universe expansion in the framework of the Standard Model (SM) and of the nuMSM -- the minimal extension of the SM by three right-handed singlet fermions. We show that the inflationary epoch is followed by a matter dominated stage related to the Higgs field oscillations. We investigate the energy transfer from Higgs-inflaton to the SM particles and show that the radiation dominated phase of the Universe expansion starts at temperature T_r~(3-15)*10^{13} GeV, where the upper bound depends on the Higgs boson mass. We estimate the production rate of singlet fermions at preheating and find that their concentrations at T_r are negligibly small. This suggests that the sterile neutrino Dark Matter (DM) production and baryogenesis in the nuMSM with Higgs-driven inflation are low energy phenomena, having nothing to do with inflation. We study then a modification of the nuMSM, adding to its Lagrangian higher dimensional operators suppressed by the Planck scale. The role of these operators in Higgs-driven inflation is clarified. We find that these operators do not contribute to the production of Warm Dark Matter (WDM) and to baryogenesis. We also demonstrate that the sterile neutrino with mass exceeding 100 keV (a Cold Dark Matter (CDM) candidate) can be created during the reheating stage of the Universe in necessary amounts. We argue that the mass of DM sterile neutrino should not exceed few MeV in order not to overclose the Universe.

hep-ph↗
arXiv2008

Is gravitino still a warm dark matter candidate?

We make use of the phase space density approach to discuss gravitino as a warm dark matter candidate. Barring fine tuning between the reheat temperature in the Universe and superparticle masses, we find that \emph{warm} gravitinos have both appropriate total mass density, Omega_{\tilde G} = Ω_{DM} \simeq 0.2, and suitable primordial phase space density at low momenta provided that their mass is in the range 1 keV \lesssim \mg \lesssim 15 keV, the reheat temperature in the Universe is low, T_R \lesssim 10 TeV, and masses of some of the superparticles are sufficiently small, M \lesssim 350 GeV. The latter property implies that the gravitino warm dark matter scenario will be either ruled out or supported by the LHC experiments.

hep-ph↗
arXiv2008

Constraining sterile neutrino dark matter by phase-space density observations

We apply phase-space density considerations to obtain lower bounds on the mass of sterile neutrino as dark matter candidate. The bounds are different for non-resonant production, resonant production in the presence of lepton asymmetry and production in decays of heavier particles. In the former case our bound is comparable to, but independent of the Lyman-alpha bound, and together with X-ray upper limit it disfavors non-resonantly produced sterile neutrino dark matter. An interesting feature of the latter case is that warm dark matter may be composed of heavy particles.

hep-ph↗
arXiv2002

Evidence for a connection between the gamma-ray and the highest energy cosmic-ray emissions by BL Lacertae objects

A set of potentially gamma-ray--loud BL Lac objects is selected by intersecting the EGRET and BL Lac catalogs. Of the resulting 14 objects, eight are found to correlate with arrival directions of ultra--high-energy cosmic rays (UHECRs), with significance of the order of 5 sigma. This suggests that gamma-ray emission can be used as a distinctive feature of those BL Lac objects that are capable of producing UHECR.

astro-ph↗