New Constraints on the Axion–Photon Coupling Constant for Solar Axions

Resonance excitation of the ⁸³Kr first nuclear level (E = 9.4 keV) by solar axions formed via the Primakoff mechanism is sought. The γ- and X-ray photons and the conversion and Auger electrons arising from the excited-level relaxation are detected with a gas proportional counter of a low-background detector in the underground Baksan Neutrino Observatory. The following experimental constraint is obtained for the product of the axion–photon coupling constant and the axion mass:|g_Aγ × m_A| ≤ 6.3 × 10 ^-17 In the framework of the hadronic-axion model, this corresponds to a new axion-mass constraint of m_A ≤ 12.7 eV at 95% C.L.     

Search for resonant absorption of solar axions by atomic nuclei

Search for resonant absorption of solar axions by ⁵⁷Fe and ¹⁶⁹Tm nuclei, leading to the excitation of the first nuclear level: ⁵⁷Fe: A + ⁵⁷Fe → ⁵⁷Fe* → ⁵⁷Fe + γ and A + ¹⁶⁹Tm → ¹⁶⁹Tm* → ¹⁶⁹Tm + γ, has been performed. To this end, the energy spectra of the Si(Li) detector with ⁵⁷Fe and ¹⁶⁹Tm targets have been measured. The detector and targets were located in a low-background setup equipped with passive and active shields. A new upper limit on the axion mass: m _A ≤ 330 eV (90% confidence level) has been established from the spectrum of ⁵⁷Fe (30 days). Measurements with a ¹⁶⁹Tm target during 8 days gave a new upper limit on the product of the axion-photon coupling constant and the axion mass: g _Aγ (GeV^?1) × m _A (eV) ≤ 2.9 × 10^?4 (90% confidence level).     

Search for solar axions emitted in an <Emphasis Type="Italic">M</Emphasis>1 transition in <Superscript>7</Superscript>Li* nuclei

The resonance absorption of solar axions by ⁷Li nuclei, which is accompanied by the excitation of the first nuclear level of lithium a + ⁷Li → ⁷Li* → ⁷Li + γ, is sought. To this end, the energy spectrum has been measured by an HPGe detector that is surrounded by a LiOH layer. A new upper limit m_a ≤ 16 keV (at 90% C.L.) has been determined for the mass of the hadron axion.     

Search for resonant absorption of solar axions emitted in an <Emphasis Type="Italic">M</Emphasis>1 transition in <Superscript>57</Superscript>Fe nuclei

The resonant absorption of solar axions by ⁵⁷Fe nuclei, which is accompanied by the excitation of the first excited nuclear level: A + ⁵⁷Fe → ⁵⁷Fe* → ⁵⁷Fe + γ(14.4 keV), is sought. To seek 14.4-keV photons, a Si(Li) detector and an enriched ⁵⁷Fe target are used. The detector and target are placed in a low-background setup equipped with passive and active shieldings. As a result, a new upper limit m _A ≤ 360 eV (at 90% C.L.) has been determined for the axion mass.     

Resonant mechanism of axion photoproduction in a magnetized electron gas

It was shown that the contribution of diagrams with electron-positron vacuum excitation in a strong magnetic field B ? B ₀ = m ²/e = 4.41 × 10¹³ G in the Compton mechanism of axion production γe → ae at temperatures on the order of the axion mass exceeds the contribution of the “simple” Compton diagram and the contribution of the neutrino production γe → (ν\(\bar \nu \))e to the radiation power by many orders of magnitude. The conclusion is made on the probable axionic nature of the cold hidden mass of the Universe.     

The minimal axion minimal linear $$\sigma $$ model

The minimal SO(5) / SO(4) linear \(\sigma \) model is extended including an additional complex scalar field, singlet under the global SO(5) and the Standard Model gauge symmetries. The presence of this scalar field creates the conditions to generate an axion à la KSVZ, providing a solution to the strong CP problem, or an axion-like-particle. Different choices for the PQ charges are possible and lead to physically distinct Lagrangians. The internal consistency of each model necessarily requires the study of the scalar potential describing the \(SO(5)\rightarrow SO(4)\), electroweak and PQ symmetry breaking. A single minimal scenario is identified and the associated scalar potential is minimised including counterterms needed to ensure one-loop renormalizability. In the allowed parameter space, phenomenological features of the scalar degrees of freedom, of the exotic fermions and of the axion are illustrated. Two distinct possibilities for the axion arise: either it is a QCD axion with an associated scale larger than \(\sim 10^{5}\) TeV and therefore falling in the category of the invisible axions; or it is a more massive axion-like-particle, such as a 1 GeV axion with an associated scale of \(\sim 200\) TeV, that may show up in collider searches.     

Compton polarimetry detection of small circularly and linearly polarized impurities in Mössbauer 8.4 keV (3/2-1/2) M1 γ-transition of 169Tm

The arrangement of an experiment to detect the P?odd and P, T?odd polarized part of the Mössbauer (⁺3/2– ⁺1/2) gamma transition of a deformed ¹⁶⁹Tm nucleus with an energy of 8.4 keV by Compton polarimetry is discussed. Tm ₂O₃ single crystal with a quadrupolarly split Mössbauer spectrum is proposed as a resonance polarizer. A Be-scatterer-based Compton polarimeter and a synchronously detecting system will be used to measure the P-odd circular polarization P_Cand P, T-odd linear polarization P_L.The expected accuracy of measuring the relative magnitude of the P, T-odd contribution is about 1% of the magnitude of usual weak nucleon–nucleon interaction.     

The effect of concentration of <Emphasis Type="Bold">H</Emphasis> <Subscript> <Emphasis Type="Bold">2</Emphasis> </Subscript> physisorption on the current–voltage characteristic of armchair BN nanotubes in CNT–BNNT–CNT set

In this research, we have studied physisorption of hydrogen molecules on armchair boron nitride (BN) nanotube (3,3) using density functional methods and its effect on the current–voltage (I–V) characteristic of the nanotube as a function of concentration using Green’s function techniques. The adsorption geometries and energies, charge transfer and electron transport are calculated. It is found that H₂ physisorption can suppress the I–V characteristic of the BN nanotube, but it has no effect on the band gap of the nanotube. As the H₂ concentration increases, under the same applied bias voltage, the current through the BN nanotube first increases and then begins to decline. The current–voltage characteristic indicates that H₂ molecules can be detected by a BN-based sensor.     

Maximum Entropy Inferences on the Axion Mass in Models with Axion-Neutrino Interaction

In this work, we use the maximum entropy principle (MEP) to infer the mass of an axion which interacts to photons and neutrinos in an effective low energy theory. The Shannon entropy function to be maximized is defined in terms of the axion branching ratios. We show that MEP strongly constrains the axion mass taking into account the current experimental bounds on the neutrinos masses. Assuming that the axion is massive enough to decay into all the three neutrinos and that MEP fixes all the free parameters of the model, the inferred axion mass is in the interval 0.1 eV < m _A < 0.2 eV, which can be tested by forthcoming experiments such as IAXO. However, even in the case where MEP fixes just the axion mass and no other parameter, we found that 0.1 eV < m _A < 6.3 eV in the DFSZ model with right-handed neutrinos. Moreover, a light axion, allowed to decay to photons and the lightest neutrino only, is determined by MEP as a viable dark matter candidate.     

Quantum-Chemical Simulation of the Solvent Effect on Spontaneous Emission of Singlet Oxygen

A molecular simulation of the solvent effect on radiative rate constant k _r of singlet oxygen is carried out. This study included a search for the most probable conformations of the complexes of molecules of singlet oxygen and ten solvents and calculation of dipole moments M of transitions a¹Δ _g –b¹Σ _g ⁺ (M _a–b ) and a¹Δ _g –X³Σ _g ^- (M _a–X ) of the oxygen molecule for them. Averaging of M _a–b by conformations, taking into account the probability of their formation for complexes without atoms with a large atomic number (Cl, S), yields values that, as a rule, correlate well with the behavior of k _r in the experiment. Taking into account the possibility of decreasing the distance (compared to equilibrium) between molecules in a collision complex at room temperature made it possible to achieve satisfactory agreement of the calculated and experimental data also for complexes with CCl₄, C₂Cl₄, and CS₂. The obtained data indicate that a number of factors affect k _r . The correlation of k _r with molecular polarizability in a number of cases is due, on the one hand, to its effect on the strength of dispersion interactions in the complex and, on the other hand, to the fact that it to some extent reflects the position of the upper filled orbitals of the solvent molecule. Both factors affect the degree of mixing of the π orbitals of the singlet oxygen molecule with the orbitals of the solvent molecule, which, as was found earlier, facilitates the activation of the a¹Δ _g –b¹Σ _g ⁺ transition and the borrowing of its intensity by the a¹Δ _g –X³Σ _g ^- transition.     

Effect of incommensurate potential on the resonant tunneling through Majorana bound states on the topological superconductor chains

We study the transport through the Kitaev chain with incommensurate potentials coupled to two normal leads by the numerical operator method. We find a quantized linear conductance of e ² / h, which is independent to the disorder strength and the gate voltage in a wide range, signaling the Majorana bound states. While the incommensurate potential suppresses the current at finite voltage bias, and then narrows the linear response regime of the I-V curve which exhibits two plateaus corresponding to the superconducting gap and the band edge, respectively. The linear conductance abruptly drops to zero as the disorder strength reaches the critical value 2g _s + 2Δ with Δ the p-wave pairing amplitude and g _s the hopping between neighbor sites, corresponding to the transition from the topological superconducting phase to the Anderson localized phase. Changing the gate voltage also causes an abrupt drop of the linear conductance by driving the chain into the topologically trivial superconducting phase, whose I-V curve exhibits an exponential shape.     

Anlagerungskoeffizienten und Driftgeschwindigkeiten von Elektronen in Luft

Electron drift velocities and attachment coefficients were measured in dry air (E/p=0.1–30 V/cm Torr) and in a 9∶1 nitrogen/oxygen mixture (E/p=0.2–3 V/cm Torr) in the pressure range from 50 to 200 Torr, using a modified spark chamber technique. The primary electrons were released by anα-particle. The temporal development of the electron density in the gap was determined from the amplitude of the current due to the avalanches, which were produced by applying high voltage pulses at different delay times. — It was found that in air the dissociative attachment sets in at higherE/p (～10–15 V/cm Torr) than in oxygen. At lowerE/p three body attachment is predominant. — When the high voltage pulses were applied after the transit time of the primary electrons, electron avalanches still appeared. It was concluded that they were started by electrons which were detached from negative ions. The estimated detachment rates indicate the formation of O ₂ ^? ions at lowE/p and of O^? ions at higherE/p.     

Influence of a magnetic two-phase state on the magnetocaloric effect in the La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> manganites

The magnetocaloric effect ΔT_ex and the magnetization in La_1?xSr_xMnO₃ single crystals (x=0.1, 0.125, 0.175, 0.3) have been experimentally studied. The magnetic entropy and the magnetocaloric effect ΔT_th were computed from magnetization curves. All the samples exhibited a maximum in the ΔT_th(T) curve at T=T _max ^′ . A step was observed on the ΔT_ex(T) curve in the region of T _max ^′ , with the value of ΔT_ex on this step being substantially smaller than ΔT_th. The step on the ΔT_ex(T) curve was followed by a maximum, which appeared at a temperature 20–40 K above T _max ^′ . This anomalous behavior of ΔT_ex and ΔT_th is assigned to the coexistence of two magnetic (ferro-and antiferromagnetic) phases in the crystal. The calculated value of ΔT_th is determined primarily by the ferromagnetic part of the crystal and disregards the negative contribution from the antiferromagnetic part of the crystal to ΔT_ex.     

Parametric study of radiofrequency helium discharge under atmospheric pressure

The parameters of radiofrequency helium discharge under atmospheric pressure were studied by electrical and optical measurements using high voltage probe, current probe and optical emission spectroscopy. Two discharge modes α and γ were observed within certain limits. During α to γ mode transition, a decrease in voltage (280–168 V), current (2.05–1.61 A) and phase angle (76^°–56^°) occurred. The discharge parameters such as resistance, reactance, sheath thickness, electron density, excitation temperature and gas temperature were assessed by electrical measurements using equivalent circuit model and optical emission spectroscopy. In α mode, the discharge current increased from 1.17 to 2.05 A, electron density increased from 0.19 × 10¹² to 0.47 × 10¹² cm^?3 while sheath thickness decreased from 0.40 to 0.25 mm. The excitation temperatures in the α and γ modes were 3266 and 4500 K respectively, evaluated by Boltzmann’s plot method. The estimated gas temperature increased from 335 K in the α mode to 485 K in the γ mode, suggesting that the radiofrequency atmospheric pressure helium discharge can be used for surface treatment applications.     

Thermodynamic study of compounds of the Nd-Ba-Cu-O system

Standard enthalpies of formation for solid solutions of composition Nd_{1 + x} Ba_{2 ? x} Cu₃O _y (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa₂Cu₃O_6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy S ^o(T), the difference of enthalpies H ^o(T)-H ^o(0 K), and the reduced Gibbs energy Φ^o(T) = S ^o(T)–[H ^o(T)–H ^o(0)]/T were calculated on the basis of smoothed dependence C _p (T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd_1+x Ba_2?x Cu₃O _y . The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.     

On emission from a hydrogen-like atom

A solution of the Dirac equation for an electron in the field of a point nucleus (Ze) has been obtained as an eigenfunction of the Schrödinger Hamiltonian and the spin projection operator Σ₃. With the use of this solution, the probability W^(ν) of the emission of a neutrino per unit time from a hydrogen-like atom, \((Ze)* \to (Ze) + \nu \bar \nu\), has been calculated for the first time in the first order of the parameter Ze ? 1. The probability W^(ν) appears to be rather small, and the corresponding lifetime τ^(ν) = [W^(ν)]^–1 is much larger than the age of the Universe; correspondingly, this process cannot affect the balance of low-energy neutrinos. The smallness of W^(ν) is due not only to the presence of the obvious “weak” factor (Gm_p²)²(m/mp)⁴ in the expression for W^(ν), but also primarily to the “electromagnetic” factor (Zα)¹², which can be revealed only in a particular calculation. It has been argued within quantum electrodynamics with the mentioned wavefunctions that photon emission, (Ze)* → (Ze) + γ, can be absent (analysis of photon emission requires the further development of the method), whereas axion emission, (Ze)* → (Ze) + a, can occur, although the last two effects have not been considered in detail.     

Temperature-dependent resonant tunneling in disordered quasi-one-dimensional <Emphasis Type="Italic">N</Emphasis>–<Emphasis Type="Italic">I</Emphasis>–<Emphasis Type="Italic">N</Emphasis> junctions

Formulas are obtained for the current–voltage characteristics and conductance of a quasi-one-dimensional N–I–N junction (where N is an ordinary metal and I is an insulator) with quantum resonance percolation trajectories (QRPTs) in a disordered I-layer at temperatures T > 0 K and the energy of local single-impurity electron level being equal to the Fermi energy ε₀ = ε_F. Under these conditions, the impact QRPTs have on the current through the junctions weakens as the temperature grows, and the conductance drops; this is in contrast to the rise in conductance of an empty junction (with no impurities in the I-layer).     

Diffraction enhancement effect and new possibilities of measuring the electric charge of the neutron and its inertial-to-gravitational mass ratio

Diffraction enhancement of small effects affecting a neutron undergoing Laue diffraction at Bragg angles θ _B close to 90° is predicted and experimentally observed. The enhancement is due to the delay of the neutron inside the crystal during diffraction and is proportional to tan² θ _B. As a result, the diffraction enhancement factor may be as large as ～10⁸–10⁹. On this basis, a new method is proposed for searching for the electric charge of the neutron and for measuring the ratio of its inertial mass m _i to the gravitational mass m _G . It is shown that the accuracy of the neutron charge measurement can be improved by more than two orders of magnitude in relation to the present-day accuracy and that the ratio m _i /m _G can be measured to an precision of σ(m _i /m _G ) ～ 10^?6.     

Homogeneous nucleation in liquid nitrogen at negative pressures

The kinetics of spontaneous cavitation in liquid nitrogen at positive and negative pressures has been studied in a tension wave formed by a compression pulse reflected from the liquid–vapor interface on a thin platinum wire heated by a current pulse. The limiting tensile stresses (Δp = p_s–p, where p_s is the saturation pressure), the corresponding bubble nucleation frequencies J (10²⁰–10²² s^–1 m^–3), and temperature induced nucleation frequency growth rate G_T = dlnJ/dT have been experimentally determined. At T = 90 K, the limiting tensile stress was Δp = 8.3 MPa, which was 4.9 MPa lower than the value corresponding to the boundary of thermodynamic stability of the liquid phase (spinodal). The measurement results were compared to classical (homogeneous) nucleation theory (CNT) with and without neglect of the dependence of the surface tension of critical bubbles on their dimensions. In the latter case, the properties of new phase nuclei were described in terms of the Van der Waals theory of capillarity. The experimental data agree well with the CNT theory when it takes into account the “size effect.”