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Ivan Schmidt

Publications and source records attributed to Ivan Schmidt.

At least 55 records · Page 3Linked to original sources
arXiv2019

Distinctive features of hadronizing heavy quarks

The color field of a quark, stripped off in a hard reaction, is regenerated via gluon radiation. The space-time development of a jet is controlled by the coherence time of gluon radiation, which for heavy quarks is subject to the dead-cone effect, suppressing gluons with small transverse momenta. As a result, heavy quarks can radiate only a small fraction of the initial energy. This explains the peculiar shape of the measured heavy quark fragmentation function, which strongly peaks at large fractional momenta z. The fragmentation length distribution, related to the fragmentation function in a model independent way, turns out to be concentrated at distances much shorter than the confinement radius. This implies that the mechanisms of heavy quark fragmentation is pure perturbative.

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arXiv2019

Phenomenology of an extended IDM with loop-generated fermion mass hierarchies

We perform a comprehensive analysis of the most distinctive and important phenomenological implications of the recently proposed mechanism of sequential loop generation of strong hierarchies in the Standard Model (SM) fermion mass spectra. This mechanism is consistently realized at the level of renormalizable interactions in an extended variant of the Inert Higgs Doublet model, possessing the additional $Z_{2}^{(1)}\times Z_{2}^{(2)}$ discrete and $U_{1X}$ gauge family symmetries, while the matter sectors of the SM are extended by means of $SU_{2L}$-singlet scalars, heavy vector-like leptons and quarks, as well as right-handed neutrinos. We thoroughly analyze the most stringent constraints on the model parameter space, coming from the $Z^{\prime }$ collider searches, related to the anomaly in lepton universality, and the muon anomalous magnetic moment, as well as provide benchmark points for further tests of the model and discuss possible "standard candle" signatures relevant for future explorations.

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arXiv2019

Baryons in a soft-wall AdS-Schwarzschild approach at low temperature

Recently we derived a soft-wall AdS-Schwarzschild approach at small temperatures for the description of hadrons with integer spin and adjustable number of constituents (mesons, tetraquarks, dibaryons, etc.). In the present paper we extend our formalism to states with half-integer spin (baryons, pentaquarks, etc.), presenting analytical results for the temperature dependence of their masses and form factors.

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arXiv2019

Sequentially loop-generated quark and lepton mass hierarchies in an extended Inert Higgs Doublet model

Extended scalar and fermion sectors offer new opportunities for generating the observed strong hierarchies in the fermion mass and mixing patterns of the Standard Model (SM). In this work, we elaborate on the prospects of a particular extension of the Inert Higgs doublet model where the SM hierarchies are generated sequentially by radiative virtual corrections in a fully renormalisable way, i.e. without adding any non-renormalisable Yukawa terms or soft-breaking operators to the scalar potential. Our model has a potential to explain the recently observed $R_{K}$ and $R_{K^{\ast }}$ anomalies, thanks to the non universal $U_{1X}$ assignments of the fermionic fields that yield non universal $Z^{\prime}$ couplings to fermions. We explicitly demonstrate the power of this model for generating the realistic quark, lepton and neutrino mass spectra. In particular, we show that due to the presence of both continuous and discrete family symmetries in the considered framework, the top quark acquires a tree-level mass, lighter quarks and leptons get their masses at one- and two-loop order, while neutrino masses are generated at three-loop level. The minimal field content, particle spectra and scalar potential of this model are discussed in detail.

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arXiv2019

Low-scale seesaw from neutrino condensation

Knowledge of the mechanism of neutrino mass generation would help understand a lot more about Lepton Number Violation (LNV), the cosmological evolution of the Universe, or the evolu tion of astronomical objects. Here we propose a verifiable and viable extension of the Standard model for neutrino mass generation, with a low-scale seesaw mechanism via LNV condensation in the sector of sterile neutrinos. To prove the concept, we analyze a simplified model of just one single family of elementary particles and check it against a set of phenomenological constraints coming from electroweak symmetry breaking, neutrino masses, leptogenesis and dark matter. The model predicts (i) TeV scale quasi-degenerate heavy sterile neutrinos, suitable for leptogenesis with resonant enhancement of the CP asymmetry, (ii) a set of additional heavy Higgs bosons whose existence can be challenged at the LHC, (iii) an additional light and sterile Higgs scalar which is a candidate for decaying warm dark matter, and (iv) a majoron. Since the model is based on simple and robust principles of dynamical mass generation, its parameters are very restricted, but remarkably it is still within current phenomenological limits.

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arXiv2019

Generalized Parton Distributions from charged current meson production

In this paper we prove that the simultaneous study of both $ρ$- and $π$-meson production by charged currents in Bjorken kinematics allows for a very clean extraction of the leading twist Generalized Parton Distributions of the target, with inherent control of the contribution of higher-twist corrections. Also, it might provide target-independent constraints on the distribution amplitudes of the produced mesons. We expect that such processes might be studied either in neutrino-induced or in electron-induced processes. According to our numerical estimates, the cross-sections of these processes are within the reach of JLab and EIC experiments.

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arXiv2019

Mesons in a soft-wall AdS-Schwarzschild approach at low temperature

We derive a holographic soft-wall approach in five dimensional AdS-Schwarzschild space for the description of mesons at finite temperature. In this first application we consider the small temperature limit and derive analytical expression for the mass spectrum of mesons with adjustable quantum numbers $n$ (radial number), $L$ (angular orbital momentum) and $J$ (total angular momentum). We explicitly separate the contribution at zero temperature and the leading order temperature correction. The temperature corrections arise from the temperature dependence of the dilaton parameter (which is the parameter of spontaneous breaking of chiral symmetry related to the pseudoscalar meson decay constant) and the warping of the AdS metric due to temperature. We extend our results to any hadron with integer spin (tetraquarks, dibaryons, etc.). We present numerical analysis for the temperature dependence of meson masses and form factors.

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arXiv2019

Bounds on lepton flavor violating physics and decays of neutral mesons from $τ(μ) \to 3 \ell, \ell γγ$-decays

We study two- and three-body lepton flavor violating (LFV) decays involving leptons and neutral vector bosons $V=ρ^0, ω, ϕ, J/ψ, Υ, Z^0$, as well as pseudo-scalar $P=π^0, η, η', η_c$ and scalar $S=f_0(500), f_0(980), a_0(980), χ_{c0}(1P)$ mesons, without referring to a specific mechanism of LFV realization. In particular, we relate the rates of the three-body LFV decays $τ(μ) \to 3 \ell$, where $\ell = μ$ or $e$, to the two-body LFV decays $(V,P) \to τμ(τe, μe)$, where $V$ and $P$ play the role of intermediate resonances in the decay process $τ(μ) \to 3 \ell$. From the experimental upper bounds for the branching ratios of $τ(μ) \to 3 \ell$ decays, we derive upper limits for the branching ratios of $(V,P) \to τμ(τe, μe)$. We compare our results to the available experimental data and known theoretical upper limits from previous studies of LFV processes, and find that some of our limits are several orders of magnitude more stringent. Using the idea of quark-hadron duality, we extract limits on various quark-lepton dimension-six LFV operators from data on lepton decays. Some of these limits are either new or stronger than those existing in the literature.

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arXiv2018

Deeply virtual meson production on neutrons

In this paper we analyze in detail how the measurements of exclusive electroproduction of mesons on neutrons would complement the studies of generalized parton distributions (GPDs) of the proton, providing independent experimental observables. Some of these processes on neutrons have very distinctive features, and thus we expect that measurements on liquid deuterium would allow to clearly distinguish them from similar processes on protons, giving a very clean probe of the GPD. In the case of charged meson production, all produced hadrons are charged, and for this reason we expect that the kinematics of this process could be easily reconstructed. We estimate the cross-sections in the kinematics of the Jefferson Laboratory experiments using current phenomenological GPD models.

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arXiv2018

A variant of 3-3-1 model for the generation of the SM fermion mass and mixing pattern

We propose an extension of the 3-3-1 model with an additional symmetry group $Z_{2}\times Z_{4} \times U(1)_{L_g}$ and an extended scalar sector. To our best knowledge this is the first example of a renormalizable 3-3-1 model, which allows explanation of the SM fermion mass hierarchy by a sequential loop suppression: tree-level top and exotic fermion masses, 1-loop bottom, charm, tau and muon masses; 2-loop masses for the light up, down, strange quarks as well as for the electron. The light active neutrino masses are generated from a combination of linear and inverse seesaw mechanisms at two loop level. The model also has viable fermionic and scalar dark matter candidates.

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arXiv2018

Digluon contribution to $J/ψ$ production

In this paper we study the contribution of the double parton distributions of gluons to the charmonium production. Despite being suppressed in the heavy quark mass limit, numerically this contribution gives a sizeable correction to the leading order $k_{T}$ factorization result in LHC kinematics due to enhancement of gluonic densities in the small Bjorken $x_{B}$ limit. This contribution is not suppressed at large $J/ψ$ momenta $p_{T}$ and thus presents one of the complementary mechanisms of charmonia production in this kinematics.

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arXiv2017

Electromagnetic structure of nucleon and Roper in soft-wall AdS/QCD

We present an improved study of the electromagnetic form factors of the nucleon and of the Roper-nucleon transition using an extended version of the effective action of soft-wall AdS/QCD. We include novel contribution from additional non-minimal terms, which do not renormalize the charge and do not change the normalization of the corresponding form factors, but the inclusion of these terms results in an important contribution to the momentum dependence of the form factors and helicity amplitudes.

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arXiv2017

Role of QCD compositeness in the production of scalar and tensor mesons through single-photon annihilation $e^+ e^- \to γ^* \to γS(T)$

We study the exclusive production of scalar $S = 0^{++}$ and tensor $T = 2^{++}$ mesons through single-photon annihilation $e^+ e^- \to γ^* \to γS(T)$. Using QCD compositeness of the involved hadrons considered as quark-antiquark systems, the prediction for the scaling of the differential cross sections of these processes is $dσ/dt \sim 1/s^3$ at large $s$. We further derive the scaling of the $γ^\ast \to γS$ and $γ^\ast \to γT$ transition form factors: $F_{γ^\astγS}(s) \sim 1/s$ and $F_{γ^\astγT}(s) \sim 1/s^2$. Results for the respective cross sections of the scalar and tensor meson production are presented. Note, when scalar and tensor mesons are considered as tetraquark systems of two tightly bound color diquarks, corresponding to them transition form factors and differential cross sections have the same falloffs as in case of quark-antiquark picture. For other tetraquark or two-hadron molecules configurations the transition form factors $F_{γ^\astγS(T)}(s)$ and the differential cross section $dσ/dt$ have additional $1/s$ and $1/s^2$ falloffs, respectively.

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arXiv2017

GPDs from charged current meson production in $ep$ experiments

We suggest that generalized parton distributions can be probed in charged current meson production process, $ep\toν_{e}π^{-}p$. In contrast to pion photoproduction, this process is sensitive to the unpolarized GPDs $H,\,E$, and for this reason has a very small contamination by higher twist and Bethe-Heitler type contributions. Since all produced hadrons are charged, we expect that the kinematics of this process could be easily reconstructed. We estimated the cross-sections in the kinematics of upgraded 12 GeV Jefferson Laboratory experiments and found that thanks to large luminosity the process can be measured with reasonable statistics.

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arXiv2017

Radiative Seesaw-type Mechanism of Fermion Masses and Non-trivial Quark Mixing

We propose a predictive inert 2 Higgs doublet model, where the Standard Model (SM) symmetry is extended by $S_{3}\otimes Z_{2}\otimes Z_{12}$ and the field content is enlarged by extra scalar fields, charged exotic fermions and two heavy right-handed Majorana neutrinos. The charged exotic fermions generate a nontrivial quark mixing and provide one-loop-level masses for the first- and second-generation charged fermions. The masses of the light active neutrinos are generated from a one loop-level radiative seesaw mechanism. Our model successfully explains the observed SM fermion mass and mixing pattern.

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arXiv2017

Transverse momentum spectrum of dilepton pair in the unpolarized $π^-N$ Drell-Yan process within TMD factorization

We study the transverse momentum spectrum of dilepton produced in the unpolarized $π^- N$ Drell-Yan process, using transverse momentum dependent factorization up to next-to-logarithmic order of QCD. We extract the nonperturbative Sudakov form factor for the pion in the evolution formalism of the unpolarized TMD distribution function, by fitting the experimental data collected by the E615 Collaboration at Fermilab. With the extracted Sudakov factor, we calculate the normalized differential cross section with respect to transverse momentum of the dimuon and compare it with the recent measurement by the COMPASS Collaboration.

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arXiv2017

Transverse polarization of the $Λ$ hyperon from unpolarized quark fragmentation in the diquark model

We investigate the spin-dependent (naive) T-odd fragmentation function $D^\perp_{1T}$, which can provide an explanation on the transverse polarization of the $Λ^0$ hyperon produced in an unpolarized process. We calculate $D^\perp_{1T}$ for light flavors in the spectator diquark model, with a Gaussian form factor at the hyperon-quark-diquark vertex. We include in the calculation both the scalar diquark and axial-vector diquark spectators. We determine the values of the model parameters by fitting the unpolarized fragmentation function $D^Λ_1$ to the DSV parametrization for $D^Λ_1$. In addition, we compute the longitudinal polarization fragmentation function $G^Λ_1$ and compare it with the known parametrization of $G^Λ_1$. We also estimate the transverse polarizations of $Λ$ production, in both semi-inclusive deep inelastic scattering and single inclusive $e^+e^-$ annihilation.

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