arXiv subjects

D. Antonov

Publications and source records attributed to D. Antonov.

15 recordsLinked to original sources

arXiv2016

Towards optimized surface $δ$-profiles of nitrogen-vacancy centers activated by helium irradiation in diamond

The negatively-charged nitrogen-vacancy (NV) center in diamond has been shown recently as an excellent sensor for external spins. Nevertheless, their optimum engineering in the near-surface region still requires quantitative knowledge in regard to their activation by vacancy capture during thermal annealing. To this aim, we report on the depth profiles of near-surface helium-induced NV centers (and related helium defects) by step-etching with nanometer resolution. This provides insights into the efficiency of vacancy diffusion and recombination paths concurrent to the formation of NV centers. It was found that the range of efficient formation of NV centers is limited only to approximately $10$ to $15\,$nm (radius) around the initial ion track of irradiating helium atoms. Using this information we demonstrate the fabrication of nanometric-thin ($δ$) profiles of NV centers for sensing external spins at the diamond surface based on a three-step approach, which comprises (i) nitrogen-doped epitaxial CVD diamond overgrowth, (ii) activation of NV centers by low-energy helium irradiation and thermal annealing, and (iii) controlled layer thinning by low-damage plasma etching. Spin coherence times (Hahn echo) ranging up to $50\,$ $μ$s are demonstrated at depths of less than $5\,$nm in material with $1.1\,\%$ of $^{13}$C (depth estimated by spin relaxation (T$_1$) measurements). At the end, the limits of the helium irradiation technique at high ion fluences are also experimentally investigated.

cond-mat.mes-hall↗

arXiv2012

Regge-like quark-antiquark excitations in the effective-action formalism

Radial excitations of the quark-antiquark string sweeping the Wilson-loop area are considered in the framework of the effective-action formalism. Identifying these excitations with the daughter Regge trajectories, we find corrections which they produce to the constituent quark mass. The energy of the quark-antiquark pair turns out to be mostly saturated by the constituent quark masses, rather than by the elongation of the quark-antiquark string. Specifically, while the constituent quark mass turns out to increase as the square root of the radial-excitation quantum number, the energy of the string increases only as the fourth root of that number.

hep-ph↗

arXiv2010

QCD relics from the early Universe

We suggest the possibility of creation in the early Universe of stable domains of radius a few kilometers wide, formed by coherently excited states of $π$-mesons. Such domains appear dark to an external observer, since the decay rate of the said coherent pionic states into photons is vanishingly small. The related thermal insulation of the domains from the outer world could have allowed them to survive till present days. The estimated maximum radius and the period of rotation of such objects turn out to be compatible with those of certain pulsars.

hep-ph↗

arXiv2010

Quantifying zigzag motion of quarks

The quark condensate is calculated in terms of the effective string tension and the constituent quark mass. For 3 colors and 2 light flavors, the constituent mass is bounded from below by the value of 460 MeV. This value is only accessible when the string tension decreases linearly with the Schwinger proper time. For this reason, the Hausdorff dimension of a light-quark trajectory is equal to 4, indicating that these trajectories are similar to branched polymers, which can describe a weak first-order deconfinement phase transition in SU(3) Yang-Mills theory. Using this indication, we develop a gluon-chain model based on such trajectories.

hep-ph↗

arXiv2009

Pressure and interaction measure of the gluon plasma

We explore the thermodynamics of the gluon plasma in SU(3) Yang-Mills theory emerging from the non-trivial spatial dynamics of valence gluons. The lattice data suggest that these gluons interact with each other linearly at large spatial separations. At high temperatures, valence gluons should reproduce the pressure of the non-interacting Stefan-Boltzmann plasma along with the leading perturbative correction. These properties of valence gluons can be modeled in terms of the integral over their trajectories. We calculate such a world-line integral analytically and obtain the pressure and the interaction measure $(\varepsilon-3p)/T^4$ of the gluon plasma. Additionally, we account for the contributions of stochastic background fields to these thermodynamic quantities. The results turn out to be in a good agreement with the corresponding lattice data. In particular, the lattice-simulated peak of the interaction measure near the deconfinement critical temperature is reproduced.

hep-ph↗

arXiv2008

Jet quenching parameter \hat q in the stochastic QCD vacuum with Landau damping

We argue that the radiative energy loss of a parton traversing the quark-gluon plasma is determined by Landau damping of soft modes in the plasma. Using this idea, we calculate the jet quenching parameter of a gluon. The calculation is done in SU(3) quenched QCD within the stochastic vacuum model. At the LHC-relevant temperatures, the result depends on the gluon condensate, the vacuum correlation length, and the gluon Debye mass. Numerically, when the temperature varies from T=T_c to T=900 MeV, the jet quenching parameter rises from \hat q=0 to approximately 1.8 GeV^2/fm. We compare our results with the predictions of perturbative QCD and other calculations.

hep-ph↗

arXiv2007

Thermal Dileptons at LHC

We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb collisions at LHC. Hadronic emission in the low-mass region is calculated using in-medium spectral functions of light vector mesons within hadronic many-body theory. In the intermediate-mass region thermal radiation from the Quark-Gluon Plasma, evaluated perturbatively with hard-thermal loop corrections, takes over. An important source over the entire mass range are decays of correlated open-charm hadrons, rendering the nuclear modification of charm and bottom spectra a critical ingredient.

hep-ph↗

arXiv2007

A Heavy Quark-Antiquark Pair in Hot QCD

Thermodynamics of a heavy quark-antiquark pair in SU(3)-QCD is studied both below and above the deconfinement critical temperature $T_c$. In the quenched case, a model of the string passing through heavy valence gluons yields a correct estimate of $T_c$ and the critical behavior of the string tension below $T_c$. For two light flavors, entropy and internal energy below $T_c$ can be obtained from the partition function of heavy-light mesons and baryons. To calculate the free energy of the system above $T_c$, we apply second-order perturbation theory in the interaction of the quark-gluon plasma constituents with the static quark-antiquark pair. The results for the entropy and internal energy, obtained both below and above $T_c$, are compared with recent lattice data.

hep-ph↗

arXiv2007

Following Gluonic World Lines to Find the QCD Coupling in the Infrared

Using a parametrization of the Wilson loop with the minimal-area law, we calculate the polarization operator of a valence gluon, which propagates in the confining background. This enables us to obtain the infrared freezing (i.e. finiteness) of the running strong coupling in the confinement phase, as well as in the deconfinement phase up to the temperature of dimensional reduction. The momentum scale defining the onset of freezing is found both analytically and numerically. The nonperturbative contribution to the thrust variable, originating from the freezing, makes the value of this variable closer to the experimental one.

hep-ph↗

arXiv2006

On the Thermodynamics of a Heavy Quark-Antiquark Pair

Thermodynamics of a heavy quark-antiquark pair in SU(3)-QCD is studied below the deconfinement critical temperature, $T_c$. In the quenched case, a model of the string passing through heavy valence gluons yields a correct estimate of $T_c$ and a behavior of the string tension near $T_c$. For two light flavors, entropy and internal energy can be obtained from the partition function of heavy-light mesons and baryons. They are in a good qualitative agreement with the lattice results.

hep-ph↗

arXiv2005

String breaking in QCD: dual superconductor vs. stochastic vacuum model

Effects of dispersion of the chromoelectric field of the flux tube on the string-breaking distance are studied. The leading-order correction is shown to slightly diminish the result following from the Schwinger formula. Instead, accounting for corrections of all orders might result, at certain values of the Landau-Ginzburg parameter, in an increase of the string-breaking distance up to one order of magnitude. An alternative formula for this distance is obtained when produced pairs are treated as holes in a confining pellicle, which spans over the contour of an external quark-antiquark pair. Generalizations of the obtained results to the cases of small temperatures, as well as temperatures close to the critical one are also discussed.

hep-th↗

arXiv2004

3D Georgi-Glashow model and confining strings at zero and finite temperatures

In this review, we discuss the confining and finite-temperature properties of the 3D SU(N) Georgi-Glashow model, and of 4D compact QED. At zero temperature, we derive string representations of both theories, thus constructing the SU(N)-version of Polyakov's theory of confining strings. We discuss the geometric properties of confining strings, as well as the appearance of the string theta-term from the field-theoretical one in 4D, and k-string tensions at N larger than 2. In particular, we point out the relevance of negative stiffness for stabilizing confining strings, an effect recently re-discovered in material science. At finite temperature, we present a derivation of the confining-string free energy and show that, at the one-loop level and for a certain class of string models in the large-D limit, it matches that of QCD at large N. This crucial matching is again a consequence of the negative stiffness. In the discussion of the finite-temperature properties of the 3D Georgi-Glashow model, in order to be closer to QCD, we mostly concentrate at the effects produced by some extensions of the model by external matter fields, such as dynamical fundamental quarks or photinos, in the supersymmetric generalization of the model.

hep-th↗

arXiv2003

A model for string-breaking in QCD

We present a model for string breaking based on the existence of chromoelectric flux tubes. We predict the form of the long-range potential, and obtain an estimate of the string breaking length. A prediction is also obtained for the behaviour with temperature of the string breaking length near the deconfinement phase transition. We plan to use this model as a guide for a program of study of string breaking on the lattice.

hep-lat↗

arXiv2003

Higgs- and quark-inspired modifications of the finite-temperature properties of the Polyakov model

(2+1)-dimensional Georgi-Glashow model, else called the Polyakov model, is explored at nonzero temperatures and in the regime when the Higgs boson is not infinitely heavy. The finiteness of the Higgs-boson mass leads to the appearance of the upper bound on the parameter of the weak-coupling approximation, necessary to maintain the stochasticity of the Higgs vacuum. The modification of the finite-temperature behavior of the model emerging due to the introduction of massless quarks is also discussed.

hep-th↗

arXiv2003

SUSY 3D Georgi-Glashow model at finite temperature

We study the finite-temperature properties of the supersymmetric version of (2+1)D Georgi-Glashow model. As opposed to its nonsupersymmetric counterpart, the parity symmetry in this theory at zero temperature is spontaneously broken by the bilinear photino condensate. We find that as the temperature is raised, the deconfinement and the parity restoration occur in this model at the same point $T_c=g^2/8π$. The transition is continuous, but is not of the Ising type as in nonsupersymmetric Georgi-Glashow model, but rather of the Berezinsky-Kosterlitz-Thouless type as in $Z_4$-invariant spin model.

hep-th↗