Definite Spin Research Articles

Quantum field theory, worldline theory, and spin magnitude change in orbital evolution

A previous paper [Z. Bern , Binary dynamics through the fifth power of spin at O(G2), ] identified a puzzle stemming from the amplitudes-based approach to spinning bodies in general relativity: additional Wilson coefficients appear compared to current worldline approaches to conservative dynamics of generic astrophysical objects, including neutron stars. In this paper we clarify the nature of analogous Wilson coefficients in the simpler theory of electrodynamics. We analyze the original field-theory construction, identifying definite-spin states some of which have negative norms, and relating the additional Wilson coefficients in the classical theory to transitions between different quantum spin states. We produce a new version of the theory which also has additional Wilson coefficients, but no negative-norm states. We match, through O(α2) and O(S2), the Compton amplitudes of these field theories with those of a modified worldline theory with extra degrees of freedom introduced by releasing the spin supplementary condition. We build an effective two-body Hamiltonian that matches the impulse and spin kick of the modified field theory and of the worldline theory, displaying additional Wilson coefficients compared to standard worldline approaches. The results are then compactly expressed in terms of an eikonal formula. Our key conclusion is that, contrary to standard approaches, while the magnitude of the spin tensor is still conserved, the magnitude of the spin vector can change under conserved Hamiltonian dynamics and this change is governed by the additional Wilson coefficients. For specific values of Wilson coefficients the results are equivalent to those from a definite spin obeying the spin supplementary condition, but for generic values they are physically inequivalent. These results warrant detailed studies of the corresponding issues in general relativity. Published by the American Physical Society 2024

Covariant Cubic Interacting Vertices for Massless and Massive Integer Higher Spin Fields

We develop the BRST approach to construct the general off-shell local Lorentz covariant cubic interaction vertices for irreducible massless and massive higher spin fields on d-dimensional Minkowski space. We consider two different cases for interacting higher spin fields: with one massive and two massless; two massive, both with coinciding and with different masses and one massless field of spins s1,s2,s3. Unlike the previous results on cubic vertices we extend our earlier result in (Buchbinder, I.L.; et al. Phys. Lett. B 2021, 820, 136470) for massless fields and employ the complete BRST operator, including the trace constraints, which is used to formulate an irreducible representation with definite integer spin. We generalize the cubic vertices proposed for reducible higher spin fields in (Metsaev, R.R. Phys. Lett. B 2013, 720, 237) in the form of multiplicative and non-multiplicative BRST-closed constituents and calculate the new contributions to the vertex, which contains the additional terms with a smaller number of space-time derivatives. We prove that without traceless conditions for the cubic vertices in (Metsaev, R.R. Phys. Lett. B 2013, 720, 237) it is impossible to provide the noncontradictory Lagrangian dynamics and find explicit traceless solution for these vertices. As the examples, we explicitly construct the interacting Lagrangians for the massive spin of the s field and the massless scalars, both with and without auxiliary fields. The interacting models with different combinations of triples higher spin fields: massive spin s with massless scalar and vector fields and with two vector fields; massless helicity λ with massless scalar and massive vector fields; two massive fields of spins s, 0 and massless scalar is also considered.

Study on the weak decay between two heavy baryons {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+) in the light-front quark model

In this work, we study the weak decay between two heavy baryons {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+) in the light-front quark model where three-quark picture is employed for baryon. We derive general form of transition amplitude of {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+), and analyze two specific cases of transitions: the weak decays of single heavy baryon Sigma _{b} rightarrow Sigma _{c}^* and the decays of double-charmed baryon Xi _{cc}rightarrow Sigma _{c}^*(Xi _{c}^*). We compute the hadronic form factors for the transitions and apply them to study the decay widths of the semi-leptonic {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+) lbar{nu }_l and non-leptonic {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+)M. Previously we studied the transition Sigma _{b} rightarrow Sigma _{c}^* with the quark–diquark picture of baryon in the light-front quark model. Here we revisit this transition with three-quark picture of baryon. At the quark level, the transition Sigma _{b} rightarrow Sigma _{c}^* is induced by the brightarrow c transition.The subsystem of the two unchanged light quarks which possesses definite and same spin in initial and final state can be viewed as a spectator, so the spectator approximation can be applied directly. For the weak decay of doubly charmed baryon Xi _{cc}, a c quark decays to a light quark q_1, so both the initial state cc and final state q_1q_2 (q_1 and the original q_2 in initial state may be the same flavor quarks) which possess definite spin are no longer spectators. A rearrangement of quarks for initial and final states is adopted to isolate the unchanged subsystem cq_2 which can be viewed as the spectator approximately. Future measurements on these channels will constrain the nonperturbative parameter in the wavefunctions and test the model predictions.

Thermodynamics and a definite large half-metallic spin gap along with a magnetic anisotropy in La-doped Ba[formula omitted]NiIrO[formula omitted

Electron doping (i. e., by replacing Ba+2 with La+3) impact on the electronic and magnetic properties of Ba2NiIrO6 system is investigated using ab-initio calculations with the inclusion of Hubbard parameter U along with spin–orbit coupling effects. The calculated formation energies affirm the experimental realization of all motifs at ambient conditions. Whereas, the elastic properties confirm the mechanical stability, ductility, and thermal conductivity of all the structures. It is revealed that anti-ferromagnetic/ferromagnetic (FM) interaction between Ni and Ir ions are energetically stable in pristine motif having an energy band gap (Eg) of 0.70/0.35 eV using the GGA+U method without/with the inclusion of SOC effects, which is in good agreement with the recent experimental results (Feng et al., 2021). Interestingly, La-doped structures depict the half-metallic FM behavior except for 50% concentration, which results in conductivity of the spin-minority channel owing to the admixture of Ir 5d states. On the other hand, the spin-majority channels exhibit an insulating nature having a large Eg of 2.53/2.63/2.49 eV for 12.5%/25%/37.5%, which looks sufficient to restrict the spin reversal and assure high spin filtering efficiency. Moreover, La-doping leads to the existence of mixed-valence state of ＋6/＋5 having a configuration 5d3 (t2g3↑t2g0↓eg0↑eg0↓)/5d4 (t2g3↑t2g1↓eg0↑eg0↓) for Ir ion. Finally, a reasonable magneto-crystalline anisotropic constant of ∼×106 erg/cm3 in all La-doped Ba2NiIrO6 systems is predicted, which is a good signal for their potential utilization in data storage devices.

Complexity for superconformal primaries from BCH techniques

We extend existing results for the Nielsen complexity of scalar primaries and spinning primaries in four dimensions by including supersymmetry. Specifically, we study the Nielsen complexity of circuits that transform a superconformal primary with definite scaling dimension, spin and R-charge by means of continuous unitary gates from the mathfrak{su} (2, 2| mathcal{N} ) group. Our analysis makes profitable use of Baker-Campbell-Hausdorff formulas including a special class of BCH formulas we conjecture and motivate. With this approach we are able to determine the super-Kähler potential characterizing the circuit complexity geometry and obtain explicit expressions in the case of mathcal{N} = 1 and mathcal{N} = 2 supersymmetry.

Spin-locked scattering of unpolarized light by magnetoelectric coupling

Unpolarized light is ubiquitous in nature. It does not carry spin angular momentum but it can be converted to partially polarized light with spin angular momentum after scattering. In this work, we demonstrate that the unpolarized light not only possesses a definite spin state after scattering but also induces lateral separation of scattered light with opposite chiralities. Such spin-locked scattering of unpolarized light stems from the inherent property of magnetoelectric coupling of the scatterer. Moreover, the spin-locked scattering for arbitrary linearly polarized light is also investigated and compared with the case of unpolarized light. Our findings can broaden the application range of unpolarized light and open other avenues for spin-related phenomena induced by unpolarized light.

Probabilities and Certainties Within a Causally Symmetric Model

This paper is concerned with the causally symmetric version of the familiar de Broglie–Bohm interpretation, this version allowing the spacelike nonlocality and the configuration space ontology of the original model to be avoided via the addition of retrocausality. Two different features of this alternative formulation are considered here. With regard to probabilities, it is shown that the model provides a derivation of the Born rule identical to that in Bohm’s original formulation. This derivation holds just as well for a many-particle, entangled state as for a single particle. With regard to “certainties”, the description of a particle’s spin is examined within the model and it is seen that a statistical description is no longer necessary once final boundary conditions are specified in addition to the usual initial state, with the particle then possessing a definite (but hidden) value for every spin component at intermediate times. These values are consistent with being the components of a single, underlying spin vector. The case of a two-particle entangled spin state is also examined and it is found that, due to the retrocausal aspect, each particle possesses its own definite spin during the entanglement, independent of the other particle. In formulating this picture, it is demonstrated how such a realistic model can preserve Lorentz invariance in the face of Bell’s theorem and avoid the need for a preferred reference frame.

Thermodynamics and a Definite Large Half-Metallic Spin Gap Along with a Sizeable Magnetic Anisotropy in La-Doped Ba2niiro6

Thermodynamics and a Definite Large Half-Metallic Spin Gap Along with a Sizeable Magnetic Anisotropy in La-Doped Ba2niiro6

Mass spectra, wave functions and mixing effects of the (bcq) baryons

Mass spectra and wave functions of the J^P=frac{1}{2}^+ (bcq) baryons are calculated by the relativistic Bethe–Salpeter equation (BSE) with considering the mixing effects between the 1^+ and 0^+ (bc)-diquarks inside. Based on the diquark picture, the three-body problem of baryons is transformed into two two-body problems. The BSE and wave functions of the 0^+ diquark are given, and then solved numerically to obtain the effective mass spectra and form factors. Also we present the wave functions at zero point for the (bc)-diquark. Considering the obtained diquark form factors, the (bcq) baryons are then described by the BSE as the bound state of a diquark and a light quark, where the interaction kernel includes the inner transitions between the 0^+ and 1^+ diquarks. The general wave function of the frac{1}{2}^+ (bcq) baryons is constructed and solved to obtain the corresponding mass spectra. Especially, by using the obtained wave functions, the mixing effects between Xi _{bc}(Omega _{bc}) and Xi _{bc}'(Omega '_{bc}) in ground states are computed and determined to be small (sim !1%). The numerical results indicate that it is a good choice to take Xi _{bc} and Xi '_{bc} as the baryon states with the inside (bc)-diquarks occupying the definite spin.

Spin transport at a Pt/InAs quantum well interface using spin Hall and Rashba effects

In the field of spintronics, charge-to-spin conversion without a ferromagnetic material has attracted intense interest from researchers seeking to realize a fully electrical spin device because this design obviates the need for magnetic field control of magnetization. Instead of spin injection from a ferromagnetic source, spin-Hall-induced pure spin current has recently attracted considerable interest for transferring spin information into the semiconductor channel. In the present work, the spin is injected from a platinum electrode via the direct spin Hall effect and is subsequently detected in a strong Rashba channel via the inverse spin Hall effect. Before being detected, the spin state is modulated by a gate voltage; the signal observed with various channel lengths and gate voltages demonstrates this Rashba precessional modulation. The addition of Zeeman precession induced by an external magnetic field provides the signal-elucidating definite spin motion in the channel and clear interplay between the Rashba and Zeeman processions. Our approach opens a fascinating possibility for realizing a ferromagnet-free system for use in low-power and high-temperature spin transistors.

Study on Xi _{cc}rightarrow Xi _c and Xi _{cc}rightarrow Xi '_c weak decays in the light-front quark model

In this work we study the weak decays of Xi _{cc}rightarrow Xi _c and Xi _{cc}rightarrow Xi '_c in the light-front quark model. Generally, a naive, but reasonable conjecture suggests that the cc subsystem in Xi _{cc} ( us pair in Xi ^{(')}_c) stands as a diquark with definite spin and color assignments. During the concerned processes, the diquark of the initial state is not a spectator, namely must be broken. A Racah transformation would decompose the original (cc)q into a combination of c(cq) components. Thus we may deal with the decaying c quark alone while keeping the (cq) subsystem as a spectator. With the re-arrangement of the inner structure we calculate the form factors numerically and then obtain the rates of semi-leptonic decays and non-leptonic decays, which will be measured in the future.

Solutions for mixed states in open bosonic string theory

We describe the family of normalizable solutions in linearized open string field theory, defined by QΨ0=0 (Q is BRST charge) understood in the sense <<QΨ0,Φ>>=0 for an arbitrary string field Φ. The solutions depend on shifted partition numbers and are parametrized in terms of values of ζ-function at pairs of positive numbers greater than 2. We argue that the operators, defined by these solutions, create mixed quantum-mechanical states by acting on the vacuum (as opposed to standard vertex operators, creating the pure states with definite masses and spins).

Investigation of room temperature ferromagnetism in transition metal doped BiFeO3

Spintronic functionality in ferromagnetic materials is a next-generation technique, to be used in data storage, high-frequency communications, and logic devices with minimum energy consumption. Ultra-low energy consumption in high-speed logic devices can be envisioned by inducing ferromagnetic behavior into room temperature multiferroic materials. However, there is a scarcity of room temperature multiferroic materials which have a definite spin degree of freedom. To fully exploit these technological challenges, we introduce the induced ferromagnetism in bismuth ferrite (BiFeO3, BFO) by doping transition metal (Cr, Ni, Co) elements. Our investigation initiates with the experimental study on chemically synthesized BiFe(1−x)MxO3 samples where x = 0.0625 (6.25%) and M = Cr, Ni and Co. Experimental findings are verified by theoretical simulation using density functional theory (DFT + U) and gauge including projector augmented wave (GIPAW) based calculation. All the experimental studies are done at room temperature while the theoretical verification using DFT is carried to understand the underlying mechanism behind the magnetic behavior of doped BiFeO3. It is done by optimizing the structural parameters comparable to the room temperature values. Microstructural and magnetic properties are studied using x-ray diffraction (XRD), transmission electron microscopy (TEM) and Vibrating sample magnetometer (VSM). All these experimental studies confirm the structural changes and induced ferromagnetism with doping. X-ray photoelectron spectroscopy (XPS) verified the reason behind this ferromagnetic property on the basis of oxygen vacancy content. Electron paramagnetic resonance (EPR) spectroscopy shows the tuning of Δg values due to enhanced magnetization.The density of states (DOS) calculations were performed on BFO (band-gap 1.89 eV) after structural optimization using DFT + U method, confirm our experimental findings. Magnetic moment values change drastically with doping elements (M), i.e. almost negligible for BFO (antiferromagnetic) to maximum (2.85 μB/f.u.) for Ni-doped sample. We also compute the EPR g-tensor using GIPAW method to confirm the tuning of Δg values due to enhanced magnetization. These results can highlight the impact and importance of suitable transition element doping to induce the room temperature ferromagnetism in BiFeO3.

Test-field limit of metric nonlinear gravity theories

In the framework of alternative metric gravity theories, it has been shown by several authors that a generic Lagrangian depending on the Riemann tensor describes a theory with 8 degrees of freedom (which reduce to 3 for f(R) Lagrangians depending only on the curvature scalar). This result is often related to a reformulation of the fourth-order equations for the metric into a set of second-order equations for a multiplet of fields, including – besides the metric – a massive scalar field and a massive spin-2 field (the latter being usually regarded as a ghost): this is commonly assumed to represent the particle spectrum of the theory. In this article we investigate an issue which does not seem to have been addressed so far: in ordinary general-relativistic field theories, all fundamental fields (i.e. fields with definite spin and mass) reduce to test fields in some appropriate limit of the model, where they cease to act as sources for the metric curvature. In this limit, each of the fundamental fields can be excited from its ground state independently from the others (which does not happen, instead, as long as the fields are coupled through the gravitational interaction). We thus address the following question: does higher-derivative gravity admit a test-field limit for its fundamental fields? It is easy to show that for a generic f(R) theory (carrying 3 d.o.f.) the test-field limit does exist; then, we consider the case of Lagrangians depending on the full Ricci tensor, relying on a previous analysis published several years ago. We show that, already for a quadratic Lagrangian, the constraint binding together the scalar field and the massive spin-2 field does not disappear in the limit where they should be expected to act as test fields. A proper test-field limit exists only for a particular choice of the coefficients in the Lagrangian, which cause the scalar field to disappear (so that the resulting model has only 7 d.o.f.). We finally consider the possible addition of an arbitrary function of the quadratic invariant of the Weyl tensor, C^{alpha }{}_{beta mu nu }C_{alpha }{}^{beta mu nu }, showing that the appearance of the Weyl tensor does not add physical degrees of freedom (in accordance to the known results for Lagrangians depending on the full Riemann tensor) and the resulting model with 8 d.o.f. still lacks a proper test-field limit: the differential constraints between the fundamental fields do not cancel out when gravitational interaction is suppressed. We argue that the lack of a test-field limit for the dynamics of the fundamental fields may constitute a serious drawback of the full 8 d.o.f. higher-order gravity models, which is not encountered in the restricted 7 d.o.f. or 3 d.o.f. cases.

Revisiting Lambda _{b}rightarrow Lambda _{c} and Sigma _{b}rightarrow Sigma _{c} weak decays in the light-front quark model

In this work, we study Lambda _{b}rightarrow Lambda _{c} and Sigma _{b}rightarrow Sigma _{c} weak decays in the light-front quark model. As is well known, the key point for such calculations is properly evaluating the hadronic transition matrix elements which are dominated by the non-perturbative QCD effect. In our calculation, we employ the light-front quark model and rather than the traditional diquark picture, we account the two spectator light quarks as individual ones. Namely during the transition, they retain their color indices, momenta and spin polarizations unchanged. Definitely, the subsystem composed of the two light quarks is still in a color-anti-triplet and possesses a definite spin, but we do not priori assume the two light quarks to be in a bound system–diquark. Our purpose is probing the diquark picture, via comparing the results with the available data, we test the validity and applicability of the diquark structure which turns a three-body problem into a two-body one, so greatly simplifies the calculation. It is indicated that the two approaches (diquark and a subsystem within which the two light quarks are free) lead to similar numerical results even though the model parameters in the two schemes might deviate slightly. Thus, the diquark approach seems sufficiently reasonable.

Shape and angular distribution of the 4.439-MeV γ -ray line from proton inelastic scattering off C12

The emission of the 4.438-MeV gamma-ray line in proton inelastic scattering off 12C has been investigated in detail. For this, two independent descriptions of the correlated scattering and emission process have been developed, one for the direct reaction mechanism and the other for the compound-nucleus (CN) component. Direct reactions were calculated in the framework of the coupled-channels formalism, while the CN component was described as a superposition of separate resonances with definite spin and parity, treated with the angular momentum coupling theory. Both components were incoherently added and compared to a comprehensive data set on measured line shapes and gamma-ray angular distributions in the proton energy range Ep = 5.44 - 25.0 MeV. In the range Ep ~ 14 - 25 MeV, good agreement with data was obtained with a dominating direct reaction component. At lower energy, an important CN component was required to describe line shape and angular distribution data. In general, a good decription of the data could be found for a CN component with spin and parity corresponding to a known nearby resonance. The new calculation improves significantly the agreement with line shape data compared to previous ones. Based on these results, predictions for line shapes and gamma-ray angular distributions up to Ep = 100 MeV were made and applied to gamma-ray emissions in solar flares and proton radiotherapy.

Neutrino propagator in media: spin properties and spectral representation

We have found that in case of propagation of neutrino in the moving matter or external magnetic field there is a fixed 4-axis of polarization, which corresponds to spin projectors commute with a propagator. It means that, states with the definite spin projection on this axis in media have a definite dispersion law. The presence of this axis essentially simplifies the eigenvalue problem and allows one to build spectral representation of the propagator in media.

Corrections of two-photon interactions in the fine and hyperfine structure of the P-energy levels of muonic hydrogen

In the framework of the quasipotential method in quantum electrodynamics we calculate corrections to the nuclear structure proportional to $r_N^2$ from two-photon exchange amplitudes in the fine and hyperfine structure of P-states in muonic hydrogen, as well as the photon-photon interaction amplitudes, leading to the exchange of the axial vector meson. In constructing the quasipotential of the muon-nucleus interaction, we use the method of projection operators on states of two particles with a definite spin and total angular momentum. Analytical calculation of the matrix elements is performed and contributions to the fine and hyperfine structure of the $2P_{1/2}$ and $2P_{3/2}$ levels are obtained.

Band head spin assignment of superdeformed bands in Hg isotopes through power index formula

The power index formula has been used to obtain the band head spin (I0) of all the superdeformed (SD) bands in Hg isotopes. A least squares fitting approach is used. The root mean square deviations between the determined and the observed transition energies are calculated by extracting the model parameters using the power index formula. Whenever definite spins are available, the determined and the observed transition energies are in accordance with each other. The computed values of dynamic moment of inertia J(2) obtained by using the power index formula and its deviation with the rotational frequency is also studied. Excellent agreement is shown between the calculated and the experimental results for J(2) versus the rotational frequency. Hence, the power index formula works very well for all the SD bands in Hg isotopes expect for 195Hg(2, 3, 4).

Genuine Multipartite Entanglement in the 3-Photon Decay of Positronium

The electron-positron annihilation into two photons is a standard technology in medicine to observe e.g. metabolic processes in human bodies. A new tomograph will provide the possibility to observe not only direct e+e− annihilations but also the 3 photons from the decay of ortho-positronium atoms formed in the body. We show in this contribution that the three-photon state with respect to polarisation degrees of freedom depends on the angles between the photons and exhibits various specific entanglement features. In particular genuine multipartite entanglement, a type of entanglement involving all degrees of freedom, is subsistent if the positronium was in a definite spin eigenstate. Remarkably, when all spin eigenstates are mixed equally, entanglement –and even stronger genuine multipartite entanglement– survives. Due to a “symmetrization” process, however, Dicke-type or W-type entanglement remains whereas GHZ-type entanglement vanishes. The survival of particular entanglement properties in the mixing scenario may make it possible to extract quantum information in the form of distinct entanglement features, e.g., from metabolic processes in human bodies.