Axion-electron Coupling Constant Research Articles

Computational mathematics applied to astrophysics: Three cases of study

The role of computational mathematics on the study of the fundamental properties of neutrinos and axions and their impact on the energy loss within stellar structure is illustrated in this work. The theoretical predictions, done with the aid of a numerical code for simulating stellar evolution, are used in three cases of interest: the number of neutrinos reaching our planet from the closest stellar system, calculated by modelling its two main stars and their corresponding neutrino spectrum; the magnitude of the neutrino magnetic dipole moment and the axion-electron coupling constant is estimated by comparing stellar models to the tip-RGB of fifty globular clusters; and, finally, the survival of the Earth, after the Sun becomes a red giant is tested for an scenario in which axions and neutrinos are being simultaneously produced within the solar core.

First axion bounds from a pulsating helium-rich white dwarf star

The Peccei-Quinn mechanism proposed to solve the CP problem of Quantum Chromodynamics has as consequence the existence of axions, hypothetical weakly interacting particles whose mass is constrained to be on the sub-eV range. If these particles exist and interact with electrons, they would be emitted from the dense interior of white dwarfs, becoming an important energy sink for the star. Due to their well known physics, white dwarfs are good laboratories to study the properties of fundamental particles such as the axions. We study the general effect of axion emission on the evolution of helium-rich white dwarfs and on their pulsational properties. To this aim, we calculate evolutionary helium-rich white dwarf models with axion emission, and assess the pulsational properties of this models. Our results indicate that the rates of change of pulsation periods are significantly affected by the existence of axions. We are able for the first time to independently constrain the mass of the axion from the study of pulsating helium-rich white dwarfs. To do this, we use an estimation of the rate of change of period of the pulsating white dwarf PG 1351+489 corresponding to the dominant pulsation period. From an asteroseismological model of PG 1351+489 we obtain gae < 3.3 × 10−13 for the axion-electron coupling constant, or macos2β ≲ 11.5 meV for the axion mass. This constraint is relaxed to gae < 5.5 × 10−13 (macos2β ≲ 19.5 meV), when no detailed asteroseismological model is adopted for the comparison with observations.

An asteroseismic constraint on the mass of the axion from the period drift of the pulsating DA white dwarf star L19-2

We employ an asteroseismic model of L19-2, a relatively massive (M⋆ ∼ 0.75 M⊙) and hot (Teff ∼ 12 100 K) pulsating DA (H-rich atmosphere) white dwarf star (DAV or ZZ Ceti variable), and use the observed values of the temporal rates of period change of its dominant pulsation modes (Π ∼ 113 s and Π ∼ 192 s), to derive a new constraint on the mass of the axion, the hypothetical non-barionic particle considered as a possible component of the dark matter of the Universe. If the asteroseismic model employed is an accurate representation of L19-2, then our results indicate hints of extra cooling in this star, compatible with emission of axions of mass ma cos2β ≲ 25 meV or an axion-electron coupling constant of gae ≲ 7 × 10−13.

Direct Dark Matter search with XENON100

The XENON100 experiment is the second phase of the XENON program for the direct detection of the dark matter in the universe. The XENON100 detector is a two-phase Time Projection Chamber filled with 161 kg of ultra pure liquid xenon. The results from 224.6 live days of dark matter search with XENON100 are presented. No evidence for dark matter in the form of WIMPs is found, excluding spin-independent WIMP-nucleon scattering cross sections above 2 $\times$ 10$^{-45}$ cm$^2$ for a 55 GeV/c$^2$ WIMP at 90% confidence level (C.L.). The most stringent limit is established on the spin-dependent WIMP-neutron interaction for WIMP masses above 6 GeV/c$^2$, with a minimum cross section of 3.5 $\times$ 10$^{-40}$ cm$^2$ (90% C.L.) for a 45 GeV/c$^2$ WIMP. The same dataset is used to search for axions and axion-like-particles. The best limits to date are set on the axion-electron coupling constant for solar axions, $g_{Ae}$ < 7.7 $\times$ 10$^{-12}$ (90% C.L.), and for axion-like-particles, $g_{Ae}$ < 1 $\times$ 10$^{-12}$ (90% C.L.) for masses between 5 and 10 keV/c$^2$.

Revisiting the axion bounds from the Galactic white dwarf luminosity function

It has been shown that the shape of the luminosity function of white dwarfs (WDLF) is a powerful tool to check for the possible existence of DFSZ-axions, a proposed but not yet detected type of weakly interacting particles. With the aim of deriving new constraints on the axion mass, we compute in this paper new theoretical WDLFs on the basis of WD evolving models that incorporate the feedback of axions on the thermal structure of the white dwarf. We find that the impact of the axion emission into the neutrino emission can not be neglected at high luminosities M Bol≲ 8) and that the axion emission needs to be incorporated self-consistently into the evolution of the white dwarfs when dealing with axion masses larger than ma cos 2β≳ 5 meV (i.e. axion-electron coupling constant gae≳ 1.4× 10-13). We went beyond previous works by including 5 different derivations of the WDLF in our analysis. Then we have performed χ2-tests to have a quantitative measure of the agreement between the theoretical WDLFs — computed under the assumptions of different axion masses and normalization methods --- and the observed WDLFs of the Galactic disk. While all the WDLF studied in this work disfavour axion masses in the range suggested by asteroseismology ma cos 2β≳ 10 meV; gae≳ 2.8× 10-13) lower axion masses can not be discarded from our current knowledge of the WDLF of the Galactic Disk. A larger set of completely independent derivations of the WDLF of the galactic disk as well as a detailed study of the uncertainties of the theoretical WDLFs is needed before quantitative constraints on the axion-electron coupling constant can be made.

First axion results from the XENON100 experiment

We present the first results of searches for axions and axion-like-particles with the XENON100 experiment. The axion-electron coupling constant, $g_{Ae}$, has been probed by exploiting the axio-electric effect in liquid xenon. A profile likelihood analysis of 224.6 live days $\times$ 34 kg exposure has shown no evidence for a signal. By rejecting $g_{Ae}$, larger than $7.7 \times 10^{-12}$ (90\% CL) in the solar axion search, we set the best limit to date on this coupling. In the frame of the DFSZ and KSVZ models, we exclude QCD axions heavier than 0.3 eV/c$^2$ and 80 eV/c$^2$, respectively. For axion-like-particles, under the assumption that they constitute the whole abundance of dark matter in our galaxy, we constrain $g_{Ae}$, to be lower than $1 \times 10^{-12}$ (90\% CL) for mass range from 1 to 40 keV/c$^2$, and set the best limit to date as well.

Search for axioelectric effect of solar axions using BGO scintillating bolometer

A search for axioelectric absorption of solar axions produced in the $ p + d \rightarrow {^3\rm{He}}+\gamma~(5.5~ \rm{MeV})$ reactions has been performed with a BGO detector placed in a low-background setup. A model-independent limit on an axion-nucleon and axion-electron coupling constant has been obtained: $| g_{Ae}\times g_{AN}^3|< 1.9\times 10^{-10}$ for 90% confidence level. The constrains of the axion-electron coupling have been obtained for hadronic axion with masses in (0.1 - 1) MeV range: $|g_{Ae}| \leq (0.96 - 8.2)\times 10^{-8}$.

Search for axioelectric effect of 5.5 MeV solar axions using BGO detectors

A search for axioelectric absorption of solar axions produced in the $ p + d \rightarrow {^3\rm{He}}+\gamma (5.5 \rm{MeV})$ reactions has been performed with a BGO detector placed in a low-background setup. A model-independent limit on an axion-nucleon and axion-electron coupling constant has been obtained: $| g_{Ae}\times g_{AN}^3|< 2.9\times 10^{-9}$ for 90% confidence level. The constrains of the axion-electron coupling have been obtained for hadronic axion with masses in (0.1 - 1) MeV range: $|g_{Ae}| \leq (1.4 - 9.7)\times 10^{-7}$.

Constraints on the axion-electron coupling constant for solar axions appearing owing to bremsstrahlung and the compton process

The axio-electric effect in silicon atoms is sought for solar axions appearing owing to bremsstrahlung and the Compton process. Axions are detected using a Si(Li) detector placed in a low-background setup. As a result, a model-independent constraint on the axion-electron coupling constant |g Ae | ≤ 2.2 × 10−10 has been obtained, which leads to the bounds m A ≤ 7.9 eV and m A ≤ 1.4 eV (at 90% C.L.) for the mass of the axion in the DFSZ and KSVZ models, respectively.

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: $g_{Ae} \leq (1-5)\times 10^{-17}$.

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.