Pairing and condensation in a resonant Bose-Fermi mixture

We study by diagrammatic methods a mixture of single-component bosons and fermions, with boson-fermion coupling tuned by a Fano-Feshbach resonance. For increasing coupling, the growing boson-fermion pairing correlations progressively reduce the boson condensation temperature and make it eventually vanish at a critical coupling. Such quantum critical point depends very weakly on the population imbalance and for vanishing boson densities coincides with that found for the polaron-molecule transition in a strongly imbalanced Fermi gas, thus bridging two quite distinct physical systems.Comment: 4 pages, 4 figure

Mass imbalance effect in resonant Bose-Fermi mixtures

We consider a homogeneous Bose-Fermi mixture, with the boson-fermion interaction tuned by a Fano-Feshbach resonance, in the presence of mass and density imbalance between the two species. By using many-body diagrammatic methods, we first study the finite-temperature phase diagram for the specific case of the mass-imbalanced mixture $^{87}$Rb $-^{40}$K for different values of the density imbalance. We then analyse the quantum phase transition associated with the disappearance at zero temperature of the boson condensate above a critical boson-fermion coupling. We find a pronounced dependence of the critical coupling on the mass ratio and a weak dependence on the density imbalance. For a vanishingly small boson density, we derive, within our approximation, the asymptotic expressions for the critical coupling in the limits of small and large mass ratios. These expressions are relevant also for the polaron-molecule transition in a Fermi mixture at small and large mass ratios. The analysis of the momentum distribution functions at sufficiently large density imbalances shows an interesting effect in the bosonic momentum distribution due to the simultaneous presence of composite fermions and unpaired fermions.Comment: Final versio

Energy of strongly attractive Bose-Fermi mixtures

We discuss how approximate theories for Bose-Fermi mixtures recover in the molecular limit the expected expression for Fermi-Fermi mixtures of molecules and unpaired fermions. In particular, we compare the energy of the system resulting from a T-matrix diagrammatic approach with that obtained with Variational and Fixed-Node Diffusion Quantum Monte Carlo methods.Comment: 5 pages, 2 figures, submitted to the EPJST volume "Novel Quantum Phases and Mesoscopic Physics in Quantum Gases

Infected pancreatic necrosis: outcomes and clinical predictors of mortality. A post hoc analysis of the MANCTRA-1 international study

: The identification of high-risk patients in the early stages of infected pancreatic necrosis (IPN) is critical, because it could help the clinicians to adopt more effective management strategies. We conducted a post hoc analysis of the MANCTRA-1 international study to assess the association between clinical risk factors and mortality among adult patients with IPN. Univariable and multivariable logistic regression models were used to identify prognostic factors of mortality. We identified 247 consecutive patients with IPN hospitalised between January 2019 and December 2020. History of uncontrolled arterial hypertension (p = 0.032; 95% CI 1.135-15.882; aOR 4.245), qSOFA (p = 0.005; 95% CI 1.359-5.879; aOR 2.828), renal failure (p = 0.022; 95% CI 1.138-5.442; aOR 2.489), and haemodynamic failure (p = 0.018; 95% CI 1.184-5.978; aOR 2.661), were identified as independent predictors of mortality in IPN patients. Cholangitis (p = 0.003; 95% CI 1.598-9.930; aOR 3.983), abdominal compartment syndrome (p = 0.032; 95% CI 1.090-6.967; aOR 2.735), and gastrointestinal/intra-abdominal bleeding (p = 0.009; 95% CI 1.286-5.712; aOR 2.710) were independently associated with the risk of mortality. Upfront open surgical necrosectomy was strongly associated with the risk of mortality (p < 0.001; 95% CI 1.912-7.442; aOR 3.772), whereas endoscopic drainage of pancreatic necrosis (p = 0.018; 95% CI 0.138-0.834; aOR 0.339) and enteral nutrition (p = 0.003; 95% CI 0.143-0.716; aOR 0.320) were found as protective factors. Organ failure, acute cholangitis, and upfront open surgical necrosectomy were the most significant predictors of mortality. Our study confirmed that, even in a subgroup of particularly ill patients such as those with IPN, upfront open surgery should be avoided as much as possible. Study protocol registered in ClinicalTrials.Gov (I.D. Number NCT04747990)

Resonant Bose-Fermi Mixtures : a T-matrix and Quantum Monte Carlo Study

In this thesis we develop the theoretical study of a novel physical system, in the context of ultracold gases. We investigate the physical behavior of a resonant Bose-Fermi mix- ture, namely, an ultracold gas made of both bosons and fermions, with a strong attractive interaction between these two components. We study homogeneous density and mass imbalanced mixtures from weak- to strong- coupling limit, comparing the results obtained with two different theoretical approaches, a many-body diagrammatic approach (the T- matrix approximation) and Quantum Monte Carlo method. By using many-body diagrammatic methods we first obtain the finite-temperature phase diagram and the thermodynamic properties of the system. We observe the presence of a quantum phase transition from the condensed (superfluid) to the normal (molecular) phase. Developing the zero-temperature limit of the same Green’s function formalism we study the effect of density and mass imbalances for the Bose-Fermi mixture. For a van- ishingly small boson density we derive the asymptotic expressions for the critical coupling in the limits of small and large mass ratios. These expressions are relevant also for the polaron-molecule transition in a strongly-imbalanced Fermi mixture, thus bridging two quite distinct physical systems. The analysis of the momentum distribution functions at sufficiently large density imbalances shows an interesting effect in the bosonic momentum distribution, due to the simultaneous presence of composite fermions and unpaired bosons. By using the corresponding retarded propagators we calculate the spectral weight func- tions and the dispersions of the bosons and of the fermions. We obtain a wide collection of single-particle intensity plots, for several values of the density and mass imbalances, which could be compared in the near future with experimental data, obtained e.g. with radio-frequency spectroscopy. We use for the first time the Quantum Monte Carlo method with Fixed-Node approxima- tion to investigate resonant Bose-Fermi mixture, from weak to the strong boson-fermion attraction. Two different nodal surfaces are used as trial wave functions in the two regimes. We obtain the equation of state of a density imbalanced mixture and we observe the presence of the quantum phase transition through the crossing of the energies, cal- culated with their respective trial wave functions. By fitting the Quantum Monte Carlo data, we can write the expressions for the energy in the superfluid and in the normal phase. A phase diagram in the coupling and boson-fermion concentration variables is then derived and the occurrence of phase separation is discussed. We compare Quantum Monte Carlo results to T-matrix calculations, finding an interesting agreement between the two results for the bosonic momentum distribution

Resonant Bose-Fermi mixtures with density and mass imbalance

We consider a homogeneous Bose-Fermi mixture, with the boson-fermion interaction tuned by a broad Fano-Feshbach resonance, in the presence of mass and density imbalance between the two species. For increasing coupling, the growing boson-fermion pairing correlations progressively reduce the boson condensation temperature and make it eventually vanish at a critical coupling. We find a pronounced dependence of the critical coupling on the mass ratio and a weak dependence on the density imbalance. For a vanishingly small boson density, we present asymptotic expressions for the critical coupling at small and large mass ratios. The analysis of the momentum distribution functions at sufficiently large density imbalance shows a peculiar feature in the bosonic momentum distribution due to the simultaneous presence of composite fermions and unpaired fermions

Bose-Fermi mixtures in the Strong-Attraction limit

3rd Scientific Day of School of Science and Technology, UNICA

Bose-Fermi mixtures in the Strong-Attraction limit

3rd Scientific Day of School of Science and Technology, UNICA