Axion-electron Coupling Research Articles

Constraints on the axion-electron coupling for solar axions produced by a Compton process and bremsstrahlung

The search for solar axions produced by Compton ($\ensuremath{\gamma}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}+A$) and bremsstrahlunglike (${e}^{\ensuremath{-}}+Z\ensuremath{\rightarrow}Z+{e}^{\ensuremath{-}}+A$) processes has been performed. The axion flux in both cases depends on the axion-electron coupling constant. The resonant excitation of the low-lying nuclear level of $^{169}\mathrm{Tm}$ was looked for: $A+^{169}\mathrm{Tm}\ensuremath{\rightarrow}^{169}\mathrm{Tm}^{*}\ensuremath{\rightarrow}^{169}\mathrm{Tm}+\ensuremath{\gamma}$ (8.41 keV). The Si(Li) detector and $^{169}\mathrm{Tm}$ target installed inside the low-background setup were used to detect 8.41 keV $\ensuremath{\gamma}$ rays. As a result, a new model-independent restriction on the axion-electron and the axion-nucleon couplings was obtained: ${g}_{Ae}\ifmmode\times\else\texttimes\fi{}|{g}_{AN}^{0}+{g}_{AN}^{3}|\ensuremath{\le}2.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$. In the model of the hadronic axion this restriction corresponds to the upper limit on the axion-electron coupling and on the axion mass ${g}_{Ae}\ifmmode\times\else\texttimes\fi{}{m}_{A}\ensuremath{\le}3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\text{ }\text{ }\mathrm{eV}$ (90% C.L.). The limits on the axion mass are ${m}_{A}\ensuremath{\le}105\text{ }\text{ }\mathrm{eV}$ and ${m}_{A}\ensuremath{\le}1.3\text{ }\text{ }\mathrm{keV}$ for the Dine-Fischler-Srednicki-Zhitnitskii- and Kim-Shifman-Vainstein-Zakharov-axion models, correspondingly (90% C.L.).

Search for solar axions produced in the p + d → 3He + A reaction

A search for the axioelectric absorption of 5.5-MeV solar axions produced in the $p+d\rightarrow \rm{^3He}+\gamma(5.5 \rm{MeV})$ reaction was performed with two BGO detectors placed inside a low-background setup. A model independent limit on axion-photon and axion-nucleon couplings was obtained: $|g_{Ae}\times g_{AN}| \leq 3.2\times 10^{-9} (m_A=0)$. Constraints on the axion-electron coupling constant were obtained for axions with masses in the $(0.1-1.0)$ MeV range: $g_{Ae}\leq (1.8-9.0)\times 10^{-7}$. The solar positron flux from $A\rightarrow e^-+e^+$ decay was determined for axions with masses $m_A > 2m_e$. Using the existing experimental data on the interplanetary positron flux, a new constraint on the axion-electron coupling constant for axions with masses in the $(1.2-5.4)$ MeV range was obtained: $g_{Ae} \leq (1-5)\times 10^{-17}$.

Search for solar hadronic axions produced by a bremsstrahlung-like process

We have searched for hadronic axions which may be produced in the Sun by a bremsstrahlung-like process, and observed in the HPGe detector by an axioelectric effect. A conservative upper limit on the hadronic axion mass of ma≲334 eV at 95% C.L. is obtained. Our experimental approach is based on the axion–electron coupling and it does not include the axion–nucleon coupling, which suffers from the large uncertainties related to the estimation of the flavor-singlet axial-vector matrix element.

888 Cranial nerve palsies in metastatic prostate caner-results of base of skull radiotherapy

We present results from a search for solar axions with the COSINE-100 experiment. We find no evidence of solar axion events from a data-set of 6,303.9 kg · days exposure and set a 90% confidence level upper limit on the axion-electron coupling, gae, of 1.70 ×10−11 for an axion mass less than 1 keV/c2. This limit excludes QCD axions heavier than 0.59 eV/c2 in the DFSZ model and 168.1 eV/c2 in the KSVZ model.

Magnetic-field influence on radiative axion decay into photons of the same polarization

The decays of a pseudoscalar particle, the axion, into two photons of the same polarization are studied in the model involving direct axion-electron coupling. These processes, which are forbidden in a vacuum because of a pseudoscalar nature of the axion, become possible in a magnetic field. It is shown that the kinematics of ultrarelativistic-axion decay substantially depends on photon polarizations. The probability of radiative axion decay in the limit of a strong magnetic field substantially exceeds the corresponding probability in a vacuum.

Propagation of axions in a strongly magnetized medium

The polarization operator of an axion in a degenerate gas of electrons occupying the ground-state Landau level in a superstrong magnetic field $H\gg H_0=m_e^2c^3/e\hbar =4.41\cdot 10^{13}$ G is investigated in a model with a tree-level axion-electron coupling. It is shown that a dynamic axion mass, which can fall within the allowed range of values $(10^{-5} eV \lesssim m_a\lesssim 10^{-2} eV)$, is generated under the conditions of strongly magnetized neutron stars. As a result, the dispersion relation for axions is appreciably different from that in a vacuum.

Axion cyclotron emissivity of magnetized white dwarfs and neutron stars

The energy loss rate of a magnetized electron gas emitting axions $a$ due to the process ${e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}+a$ is derived for arbitrary magnetic field strength $B$. Requiring that for a strongly magnetized neutron star the axion luminosity is smaller than the neutrino luminosity we obtain the bound ${g}_{\mathrm{ae}}\ensuremath{\lesssim}{10}^{\ensuremath{-}10}$ for the axion electron coupling constant. This limit is considerably weaker than the bound derived earlier by Borisov and Grishina using the same method. Applying a similar argument to magnetic white dwarf stars results in the more stringent bound ${g}_{\mathrm{ae}}\ensuremath{\lesssim}9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{(T/10}^{7}\mathrm{K}{)}^{5/4}{(B/10}^{10}\mathrm{G}{)}^{\ensuremath{-}2}$, where $T$ is the internal temperature of the white dwarf.

Axion emission from red giants and white dwarfs

Using thermal field theory methods, we recalculate axion emission from dense plasmas. We study in particular the Primakoff and the bremsstrahlung processes. The Primakoff rate is significantly suppressed at high densities, when the electrons become relativistic. However, the bound on the axion-photon coupling, G < 10 −10 GeV −1, is unaffected, as it is constrained by the evolution of HB stars, which have low densities. In contradistinction, the same relativistic effects enhance the bremsstrahlung processes. From the red giants and white dwarfs evolution, we obtain a conservative bound on the axion-electron coupling, g ae < 3 × 10 −13.

The cooling of hot white dwarfs: a theory with non-standard weak interactions, and a comparison with observations

We present calculations of the cooling evolutionary sequences of hot (T eff >12×10 3 K) white dwarf stars. The input physics is discussed in some detail, with special emphasis on the thermal conductivity and plasmon neutrino emission assumed. We suggest our own approximation for the latter. We find that the calculated effective temperature distribution of white dwarfs is rather sensitive to the assumed mass. The best fit to the observations yields the mass M=0.7 M ○. . With the inclusion of non-standard physics, we confirm the upper limit on the neutrino magnetic moment to be μ ν <10 −11 in units of the Bohr magneton. Taking into account the bremsstrahlung of axions, we find a constraint on the axion-electron coupling (the axion fine-structure constant) of α a <5×10 −26

Paraphotons and axions: Similarities in stellar emission and detection

The massless gauge boson of an extra U(1) symmetry - the paraphoton - could have low-energy effective couplings to ordinary matter. The coupling to electrons would behave much like the invisible axion-electron coupling at keV energies. We find astrophysical bounds on the paraphoton-electron coupling strength: α Γee <1.5 × 10 −22 (sun), and α Γee ≲10 −26 (while dwarfs). We also show that planned solar axion detectors would not distinguish axions and paraphotons.