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Register a new userHyperfine Suppression of $2^3{rm S}_1 - 3^3{rm P}_J$ Transitions in $^3$He
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Two anomalously weak transitions within the $2 ^3{rm S}_1~-~3 ^3{rm P}_J$ manifolds in $^3$He have been identified. Their transition strengths are measured to be 1,000 times weaker than that of the strongest transition in the same group. This dramatic suppression of transition strengths is due to the dominance of the hyperfine interaction over the fine structure interaction. An alternative selection rule based on textit{IS}-coupling (where the nuclear spin is first coupled to the total electron spin) is proposed. This provides qualitative understanding of the transition strengths. It is shown that the small deviations from the textit{IS}-coupling model are fully accounted for by an exact diagonalization of the strongly interacting states.
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The workhorse of atomic physics, quantum electrodynamics, is one of the best-tested theories in physics. However recent discrepancies have shed doubt on its accuracy for complex atomic systems. To facilitate the development of the theory further we aim to measure transition dipole matrix elements of metastable helium (He*) (the ideal 3 body test-bed) to the highest accuracy thus far. We have undertaken a measurement of the `tune-out wavelength which occurs when the contributions to the dynamic polarizability from all atomic transitions sum to zero; thus illuminating an atom with this wavelength of light then produces no net energy shift. This provides a strict constraint on the transition dipole matrix elements without the complication and inaccuracy of other methods. Using a novel atom-laser based technique we have made the first measurement of the tune-out wavelength in metastable helium between the $3^{3}P_{1,2,3}$ and $2^{3}P_{1,2,3}$ states at 413.07(2) nm which compares well with the predicted valuecite{Mitroy2013} of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $sim$200 pK and is widely applicable to other species and areas of atom optics.
We consider string theory on AdS$_3$ $times$ (S$^3$ $times$ S$^3$ $times$ S$^1)/mathbb Z_2$, a background supporting $mathcal N=(3,3)$ spacetime supersymmetry. We propose that string theory on this background is dual to the symmetric product orbifold of $mathcal S_0/mathbb Z_2$ where $mathcal S_0$ is a theory of four free fermions and one free boson. We show that the BPS spectra of the two sides of the duality match precisely. Furthermore, we compute the elliptic genus of the dual CFT and that of the supergravity limit of string theory and demonstrate that they match, hence providing non-trivial support for the holographic proposal.
Despite quantum electrodynamics (QED) being one of the most stringently tested theories underpinning modern physics, recent precision atomic spectroscopy measurements have uncovered several small discrepancies between experiment and theory. One particularly powerful experimental observable that tests QED independently of traditional energy level measurements is the `tune-out frequency, where the dynamic polarizability vanishes and the atom does not interact with applied laser light. In this work, we measure the `tune-out frequency for the $2^{3!}S_1$ state of helium between transitions to the $2^{3!}P$ and $3^{3!}P$ manifolds and compare it to new theoretical QED calculations. The experimentally determined value of $725,736,700,$$(40_{mathrm{stat}},260_{mathrm{syst}})$ MHz is within ${sim} 2.5sigma$ of theory ($725,736,053(9)$ MHz), and importantly resolves both the QED contributions (${sim} 30 sigma$) and novel retardation (${sim} 2 sigma$) corrections.
The ${^3{rm He}}(alpha,gamma){^7{rm Be}}$ and ${^3{rm H}}(alpha,gamma){^7{rm Li}}$ astrophysical $S$ factors are calculated within the no-core shell model with continuum using a renormalized chiral nucleon-nucleon interaction. The ${^3{rm He}}(alpha,gamma){^7{rm Be}}$ astrophysical $S$ factors agree reasonably well with the experimental data while the ${^3{rm H}}(alpha,gamma){^7{rm Li}}$ ones are overestimated. The seven-nucleon bound and resonance states and the $alpha+{^3{rm He}}/{^3{rm H}}$ elastic scattering are also studied and compared with experiment. The low-lying resonance properties are rather well reproduced by our approach. At low energies, the $s$-wave phase shift, which is non-resonant, is overestimated.
The astrophysical $^{3}{rm He}(alpha, gamma)^{7}{rm Be}$ and $^{3}{rm H}(alpha, gamma)^{7}{rm Li}$ direct capture processes are studied in the framework of the two-body model with the potentials of a simple Gaussian form, which describe correctly the phase-shifts in the s-, p-, d-, and f-waves, as well as the binding energy and the asymptotic normalization constant of the ground $p_{3/2}$ and the first excited $p_{1/2}$ bound states. It is shown that the E1-transition from the initial s-wave to the final p-waves is strongly dominant in both capture reactions. On this basis the s-wave potential parameters are adjusted to reproduce the new data of the LUNA collaboration around 100 keV and the newest data at the Gamov peak estimated with the help of the observed neutrino fluxes from the Sun, $S_{34}$(23$^{+6}_{-5}$ keV)=0.548$pm$0.054 keV b for the astrophysical S-factor of the capture process $^{3}{rm He}(alpha, gamma)^{7}{rm Be}$. The resulting model describes well the astrophysical S-factor in low-energy Big Bang nucleosynthesis region of 180-400 keV, however has a tendency to underestimate the data above 0.5 MeV. Two-body potentials, adjusted on the properties of the $^7$Be nucleus, $^3{rm He}+alpha$ elastic scattering data and the astrophysical S-factor of the $^{3}{rm He}(alpha, gamma)^{7}{rm Be}$ direct capture reaction, are able to reproduce the properties of the $^7$Li nucleus, the binding energies of the ground 3/2$^-$ and first excited 1/2$^-$ states, and phase shifts of the $^3 {rm H}+alpha$ elastic scattering in partial waves. Most importantly, these potential models can successfully describe both absolute value and energy dependence of the existing experimental data for the mirror astrophysical $^{3}{rm H}(alpha, gamma)^{7}{rm Li}$ capture reaction without any additional adjustment of the parameters.
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