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S. V. Demidov

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

At least 19 recordsLinked to original sources
arXiv2025

Only slightly "Amplifying nonresonant production of dark sector particles in scattering dominance regime''

In recent article [PhysRevD.109.055041 (2024)] it has been argued that production of dark photons -- hypothetical massive vectors -- in nuclear reactors via mixing with the visible photons is considerably enhanced (by a factor of 10) due to Compton scattering of the latter. We revisit the production of dark photons in the reactor environment and find that although the scattering of photons indeed leads to a larger number of produced dark photons, the overall enhancement is considerably smaller than what has been obtained in Ref. [PhysRevD.109.055041 (2024)]. Our findings are validated using GEANT simulations, which take into account oscillations between ordinary and visible photons and interaction of the latter with matter. The correction to the limit on mixing parameter between dark and visible photons is expected to be below 30% for all masses. It's application must be accompanied with an update on the original spectrum of photons produced in nuclear reactions inside the nuclear reactor.

hep-ph↗
arXiv2025

New physics from atmosphere: light sgoldstino case

In a supersymmetric model with low scale supersymmetry breaking light sgoldstinos can appear in decays of mesons abundantly produced in atmospheric showers. We obtain bounds on parameter space of such a scenario from the Super-Kamiokande atmospheric neutrino oscillation data and estimate future sensitivity of the Hyper-Kamiokande project. We find that the bounds from the Super-Kamiokande results are weaker than constraints from existing searches by other experiments while the Hyper-Kamiokande detector can probe a still allowed part of the model parameter space.

hep-ph↗
arXiv2022

Suppression exponent for multiparticle production in $λϕ^{4}$ theory

We compute the probability of producing $n$ particles from few colliding particles in the unbroken $(3+1)$-dimensional $λϕ^4$ theory. To this end we numerically implement semiclassical method of singular solutions which works at ${n \gg 1}$ in the weakly coupled regime ${λ\ll 1}$. For the first time, we obtain reliable results in the region of exceptionally large final state multiplicities ${n\gg λ^{-1}}$ where the probability decreases exponentially with $n$, ${{\cal P}(\mbox{few} \to n) \sim \exp\{f_\infty(\varepsilon) \, n\}}$, and its slope $f_{\infty}< 0$ depends on the mean kinetic energy $\varepsilon$ of produced particles. In the opposite case ${n\ll λ^{-1}}$ our data match well-known tree-level result, and they interpolate between the two limits at $n \sim λ^{-1}$. Overall, this proves exponential suppression of the multiparticle production probability at ${n\gg 1}$ and arbitrary $\varepsilon$ in the unbroken theory. Using numerical solutions, we critically analyze the mechanism for multiple Higgs boson production suggested in the literature. Application of our technique to the scalar theory with spontaneously broken symmetry can eradicate (or confirm) it in the nearest future.

hep-ph↗
arXiv2020

Bounds on non-standard interactions of neutrinos from IceCube DeepCore data

New physics in neutrino sector can reveal itself via non-standard neutrino interactions which can result in modification of the standard picture of neutrino propagation in matter. Experiments with atmospheric neutrinos has been used to probe this scenario. Using publicly available three-year low energy data in IceCube DeepCore we place bounds on the parameters $ε_{αβ}$ of non-standard neutrino interactions in propagation. We obtain restrictive constraints not only for $μτ$ sector but also for flavor changing interactions involving electron neutrinos.

hep-ph↗
arXiv2018

A search for neutrino signal from dark matter annihilation in the center of the Milky Way with Baikal NT200

We reanalyze the dataset collected during the years 1998--2003 by the deep underwater neutrino telescope NT200 in the lake Baikal with the low energy threshold (10 GeV) in searches for neutrino signal from dark matter annihilations near the center of the Milky Way. Two different approaches are used in the present analysis: counting events in the cones around the direction towards the Galactic Center and the maximum likelihood method. We assume that the dark matter particles annihilate dominantly over one of the annihilation channels $b\bar{b}$, $W^+W^-$, $τ^+τ^-$, $μ^+μ^-$ or $ν\barν$. No significant excess of events towards the Galactic Center over expected neutrino background of atmospheric origin is found and we derive 90% CL upper limits on the annihilation cross section of dark matter.

astro-ph.HE↗
arXiv2018

Gravitational waves from phase transition in split NMSSM

We discuss gravitational wave signal from the strongly first order electroweak phase transition in the split NMSSM. We find that for sets of parameters predicting successful electroweak baryogenesis the gravitational wave signal can be within the reach of future experiments LISA, BBO and Ultimate DECIGO.

hep-ph↗
arXiv2018

Numerical study of multiparticle scattering in $λϕ^4$ theory

We study numerically classical collisions of waves in $λϕ^4$ theory. These processes correspond to multiparticle scattering in the semiclassical regime. Parametrizing initial and final wavepackets by energy $E$ and particle numbers $N_{i}$, $N_{f}$ we find classically allowed region in the parameter space. We describe properties of the scattering solutions at the boundary of the classically allowed region. We comment on the implications of our results for multiparticle production in the quantum regime.

hep-ph↗
arXiv2018

Non-standard interactions and neutrinos from dark matter annihilation in the Sun

We perform an analysis of the influence of non-standard neutrino interactions (NSI) on neutrino signal from dark matter annihilations in the Sun. Taking experimentally allowed benchmark values for the matter NSI parameters we show that the evolution of such neutrinos with energies at GeV scale can be considerably modified. We simulate propagation of neutrinos from the Sun to the Earth for realistic dark matter annihilation channels and find that the matter NSI can result in at most 30% correction to the signal rate of muon track events at neutrino telescopes. Still present experimental bounds on dark matter from these searches are robust in the presence of NSI within considerable part of their allowed parameter space. At the same time electron neutrino flux from dark matter annihilation in the Sun can be changed by a factor of few.

hep-ph↗
arXiv2017

Low scale supersymmetry at the LHC with jet and missing energy signature

If supersymmetry is broken at TeV scale, particles from sector responsible for supersymmetry breaking - goldstino and sgoldstinos - can reveal themselves already at the LHC experiments. We discuss bounds on supersymmetry breaking scale from the LHC searches for events with a jet plus missing momentum signature focusing on the case of TeV scale sgoldstinos. We show that contribution of light sgoldstinos to the cross section of of gravitino pair production with a jet can be sizable and the bounds on the gravitino mass can be stronger by up to a factor of 2 as compared to those obtained in the heavy sgoldstino limit. We compare these bounds on parameters of the model to those obtained with the results of ATLAS and CMS searches for dijet resonances.

hep-ph↗
arXiv2016

Dark matter constraints from an observation of dSphs and the LMC with the Baikal NT200

In present analysis we complete search for a dark matter signal with the Baikal neutrino telescope NT200 from potential sources in the sky. We use five years of data and look for neutrinos from dark matter annihilations in the dwarfs spheroidal galaxies in the Southern hemisphere and the Large Magellanic Cloud known as the largest and close satellite galaxy of the Milky Way. We do not find any excess in observed data over expected background from the atmospheric neutrinos towards the LMC or any of tested 22 dwarfs. We perform a joint likelihood analysis on the sample of five selected dwarfs and found a concordance of the data with null hypothesis of the background-only observation. We derive 90% CL upper limits on the cross section of annihilating dark matter particles of mass between 30 GeV and 10 TeV into several channels both in our combined analysis of the dwarfs and in a particular analysis towards the LMC.

astro-ph.HE↗
arXiv2016

Lepton flavor-violating decays of the Higgs boson from sgoldstino mixing

We study lepton flavor violation in a class of supersymmetric models with light sgoldstino - scalar superpartner of Goldstone fermions responsible for spontaneous supersymmetry breaking. Sgoldstino couplings to the Standard Model (SM) fermions are determined by the MSSM soft terms and, in general, provide with flavor violation in this sector. Sgoldstino admixture to the lightest Higgs boson results in changes of its coupling constants and, in particular, leads to lepton flavor-violating decay $h\toτμ$ of the Higgs resonance. We discuss viability and phenomenological consequences of this scenario.

hep-ph↗
arXiv2016

Split NMSSM with electroweak baryogenesis

In light of the Higgs boson discovery we reconsider generation of the baryon asymmetry in the non-minimal split Supersymmetry model with an additional singlet superfield in the Higgs sector. We find that successful baryogenesis during the first order electroweak phase transition is possible within phenomenologically viable part of the model parameter space. We discuss several phenomenological consequences of this scenario, namely, predictions for the electric dipole moments of electron and neutron and collider signatures of light charginos and neutralinos.

hep-ph↗
arXiv2016

Nucleon-decay-like signatures of Hylogenesis

We consider nucleon-decay-like signatures of the hylogenesis, a variant of the antibaryonic dark matter model. For the interaction between visible and dark matter sectors through the neutron portal, we calculate the rates of dark matter scatterings off neutron which mimic neutron-decay processes $n\to νγ$ and $n\to νe^+ e^-$ with richer kinematics. We obtain bounds on the model parameters from nonobservation of the neutron decays by applying the kinematical cuts adopted in the experimental analyses. The bounds are generally (much) weaker than those coming from the recently performed study of events with a single jet of high transverse momentum and missing energy observed at the LHC. Then we suggest several new nucleon-decay like processes with two mesons in the final state and estimate (accounting for the LHC constraints) the lower limits on the nucleon lifetime with respect to these channels. The obtained values appear to be promising for probing the antibaryonic dark matter at future underground experiments like HyperK and DUNE.

hep-ph↗
arXiv2016

On sgoldstino interpretation of the diphoton excess

We point out that the diphoton excess at about 750 GeV recently discovered by the LHC experiments can be explained within supersymmetric models with low scale supersymmetry breaking with sgoldstino as a natural candidate. We discuss phenomenological consequences of this scenario describing possible signatures to test this hypothesis.

hep-ph↗
arXiv2015

Baikal-GVD: first cluster Dubna

In April 2015 the demonstration cluster "Dubna" was deployed and started to take data in Lake Baikal. This array is the first cluster of the cubic kilometer scale Gigaton Volume Detector (Baikal-GVD), which is constructed in Lake Baikal. In this contribution we will review the design and status of the array.

physics.ins-det↗
arXiv2015

Semiclassical description of soliton-antisoliton pair production in particle collisions

We develop a consistent semiclassical method to calculate the probability of topological soliton-antisoliton pair production in collisions of elementary particles. In our method one adds an auxiliary external field pulling the soliton and antisoliton in the opposite directions. This transforms the original scattering process into a Schwinger pair creation of the solitons induced by the particle collision. One describes the Schwinger process semiclassically and recovers the original scattering probability in the limit of vanishing external field. We illustrate the method in (1+1)-dimensional scalar field model where the suppression exponents of soliton-antisoliton production in the multiparticle and two-particle collisions are computed numerically.

hep-th↗
arXiv2015

Sgoldstino-Higgs mixing in models with low-scale supersymmetry breaking

We consider a supersymmetric extension of the Standard Model with low-scale supersymmetry breaking. Besides usual superpartners it contains additional chiral goldstino supermultiplet whose scalar components - sgoldstinos can mix with scalars from the Higgs sector of the model. We show that this mixing can have considerable impact on phenomenology of the lightest Higgs boson and scalar sgoldstino. In particular, the latter can be a good candidate for explanation of 2-sigma LEP excess with mass around 98 GeV.

hep-ph↗