Production of 
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 and a photon in 
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 annihilation

Braaten, Eric; He, Li-Ping; Ingles, Kevin

doi:10.1103/physrevd.101.014021

Cited by 31 publications

(29 citation statements)

References 63 publications

(169 reference statements)

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“…Thus, the number of atoms transferred by the rf pulse at high frequencies in linear response is ∝ C/ω 3/2 [5,27]. Including final state interactions, the general expression for the rf transfer rate in a gas with unitarity-limited initial state interactions is [60]:…”

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confidence: 99%

Spectral Response and Contact of the Unitary Fermi Gas

et al. 2019

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We measure radio frequency (rf) spectra of the homogeneous unitary Fermi gas at temperatures ranging from the Boltzmann regime through quantum degeneracy and across the superfluid transition. For all temperatures, a single spectral peak is observed. Its position smoothly evolves from the bare atomic resonance in the Boltzmann regime to a frequency corresponding to nearly one Fermi energy at the lowest temperatures. At high temperatures, the peak width reflects the scattering rate of the atoms, while at low temperatures, the width is set by the size of fermion pairs. Above the superfluid transition, and approaching the quantum critical regime, the width increases linearly with temperature, indicating non-Fermi-liquid behavior. From the wings of the rf spectra, we obtain the contact, quantifying the strength of short-range pair correlations. We find that the contact rapidly increases as the gas is cooled below the superfluid transition.PACS numbers: 03.75. Ss, 05.30.Fk, 51.30.+i, 71.18.+y Understanding fermion pairing and pair correlations is of central relevance to strongly interacting Fermi systems such as nuclei [1,2], ultracold gases [3-6], liquid 3 He [7], high temperature superconductors [8], and neutron stars [9]. Strong interactions on the order of the Fermi energy challenge theoretical approaches, especially methods that predict dynamic properties such as transport or the spectral response at finite temperature [10]. Atomic Fermi gases at Feshbach resonances realize a paradigmatic system where the gas becomes as strongly interacting as allowed by unitarity [3][4][5][6]11]. Here, the system becomes universal, requiring only two energy scales: the Fermi energy E F and thermal energy k B T , where k B is the Boltzmann constant and T is the temperature. The corresponding length scales are the interparticle spacing λ F = n −1/3 and the thermal de Broglie wavelength λ T = h/ √ 2πmk B T , where m and n are the mass and number density of the atoms respectively. When the two energy scales are comparable, the system enters a quantum critical regime separating the high temperature Boltzmann gas from the fermionic superfluid [12]. Quantum criticality is often associated with the absence of quasiparticles [10,12,13], spurring a debate on the applicability of Fermi liquid theory to the degenerate normal fluid below the Fermi temperature [14][15][16]. It has been conjectured that preformed pairs exist above T c , up to a pairing temperature T * [3,5,11,[17][18][19][20][21].Radio frequency (rf) spectroscopy measures the momentum integrated, occupied spectral function, providing a powerful tool for studying interactions and correlations in Fermi gases [22][23][24][25][26][27]. Here, a particle is ejected from the interacting many-body state and transferred into a weakly interacting final state. Shifts in rf spectra indicate attractive or repulsive interactions in the gas. At high temperatures, the width of the rf spectrum reflects the scattering rate in the gas, while at low temperatures, the width has been used to infe...

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confidence: 99%

Spectral Response and Contact of the Unitary Fermi Gas

et al. 2019

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“…(3) to remove the cutoff p c , Eq. (A·4) is found to reproduce the Tan's pressure relation, [94][95][96] 97) Comparing Eq. (A·4) with the relation between the pressure and the stress tensor,…”

Section: Appendix A: Expression Forπ Xy In the Bcs Modelmentioning

confidence: 88%

Shear Viscosity and Strong-Coupling Corrections in the BCS–BEC Crossover Regime of an Ultracold Fermi Gas

2019

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We theoretically investigate the shear viscosity η in the BCS-BEC crossover regime of an ultracold Fermi gas with a Feshbach resonance. Within the framework of the strong-coupling self-consistent T -matrix approximation, we examine how a strong pairing interaction associated with a Feshbach resonance affects this transport coefficient, in the normal state above the superfluid phase transition temperature T c . We show that, while η diverges in both the weak-coupling BCS and strong-coupling BEC limits, it becomes small in the unitary regime. The minimum of η is obtained, not at the unitarity, but slightly in the strong-coupling BEC side. This deviation is consistent with the recent experiment on a 6 Li Fermi gas. In the weak-coupling BCS regime, we also find that η exhibits anomalous temperature dependence near T c , which is deeply related to the pseudogap phenomenon originating form strong pairing fluctuations.

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“…The hadronic decays of the X(3872) are investigated in [142][143][144][145][146][147][148][149][150][151][152][153][154][155][156]. As for radiative decays, as seen in [157][158][159][160][161][162][163][164][165][166][167][168][169][170][171], the existence of the core seems to be required, but the results depend on details of the wave function.…”

Section: +04mentioning

confidence: 99%

Heavy hadronic molecules with pion exchange and quark core couplings: a guide for practitioners

Yamaguchi

Hosaka

Takeuchi

et al. 2020

J. Phys. G: Nucl. Part. Phys.

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We discuss selected and important features of hadronic molecules as one of promising forms of exotic hadrons near thresholds. Using examples of DD * systems such as X(3872) and Z c , emphasis is put on the roles of the one pion exchange interaction between them and their coupling to intrinsic quark states. Thus hadronic molecules emerge as admixtures of the dominant long-range hadron structure and short-range quark structure. For the pion exchange interaction, properties of the tensor force are analyzed in detail. More coupled channels supply more attractions, and heavier constituents suppress kinetic energies, providing more chances to form hadronic molecules of heavy hadrons. Throughout this article, we show details of basic ideas and methods. ‡ More complete references are given in section 4.1 for X(3872) and in section 5.1 for Z c and Z b . arXiv:1908.08790v1 [hep-ph] 23 Aug 2019 § Here D ( * ) stands for either D or D * meson. In this article we do not consider systems containing strange quarks, and therefore the notation q is used for light u, d quarks.

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Production of X(3872) and a photon in e+e− annihilation

Cited by 31 publications

References 63 publications

Spectral Response and Contact of the Unitary Fermi Gas

Spectral Response and Contact of the Unitary Fermi Gas

Shear Viscosity and Strong-Coupling Corrections in the BCS–BEC Crossover Regime of an Ultracold Fermi Gas

Heavy hadronic molecules with pion exchange and quark core couplings: a guide for practitioners

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