We study a variant of the Chromo-Natural Inflation (CNI) mechanism in which the inflaton interacts only gravitationally with the CNI fields. Integrating out all the nondynamical scalar fields of the model results in a coupling between the perturbations of the inflaton and of the CNI pseudo-scalar which is significantly greater than the one obtained in the absence of the gauge CNI dynamics. We compute how this greater coupling impacts the power spectrum of the inflaton perturbations that are sourced nonlinearly by the unstable (tensor) gauge CNI modes, and we require that the amplitude of these modes is well below that of the linear perturbations. Combining this result with various constraints, including backreaction effects, the requirement of having observable and dominant sourced gravitational waves (GW), and the current upper bound on the tensor-to-scalar ratio, significantly constrains the range of parameter space where this model can produce an interesting GW signal.
Several models of inflation employing a triplet of SU(2) vectors with spatially orthogonal vacuum expectation values (VEVs) have been recently proposed. One (tensor) combination t of the vector modes is amplified in some momentum range during inflation. Due to the vector VEVs, this combination mixes with gravitational waves (GW) at the linear level, resulting in a GW amplification that has been well studied in the literature. Scalar perturbations in this class of models have been so far studied only at the linear level. We perform a first step toward the nonlinear computation using as an example the original model of Chromo-Natural Inflation. We compute the contribution to the scalar power spectrum arising from the coupling of the combination t to the inflaton. This contribution is mostly controlled by a single parameter of the model (namely, the ratio between the mass of the fluctuations of the vector field and the Hubble rate), and, for a wide range of this parameter, it can significantly affect the phenomenology obtained from the linear theory. This nonlinear contribution is significantly blue, improving the comparison between the two-point function and the Cosmic Microwave Background (CMB) data. This growth can be also relevant for smaller scale phenomenology, such as large scale structure, CMB distortions, and primordial black holes.
Motivated by some of the recent swampland conjectures, we study the implementation for the late time acceleration of the Universe of a mechanism developed by Anber and Sorbo in the context of primordial inflation, in which an axion field can slowly roll in a steep potential due to additional friction provided by its coupling to some U(1) gauge field. We first study the realization of this mechanism in N = 2 supergravity models resulting from string compactifications on Calabi-Yau manifolds. We then study the transition between matter domination and the axion domination, and show that indeed the backreaction of the produced gauge field can sufficiently slow the motion of the axion, so to produce the present accelerated era. We finally study the transition from a pre-inflationary matter or radiation domination to primordial inflation. In the regime that we could explore numerically, the evolution is characterized by stages of faster axion roll (and consequent bursts of gauge field amplification) intermitted by stages of slower roll, with a pattern that “oscillates” about the steady state Anber and Sorbo solution, but that does not appear to relax to it.
ImportanceLong-term oncologic outcomes of robotic surgery remain a hotly debated topic in surgical oncology, but sparse data have been published thus far.ObjectiveTo analyze short- and long-term outcomes of robotic liver resection (RLR) for hepatocellular carcinoma (HCC) from Western high-volume centers to assess the safety, reproducibility, and oncologic efficacy of this technique.Design, Setting, and ParticipantsThis cohort study evaluated the outcomes of patients receiving RLR vs open liver resection (OLR) for HCC between 2010 and 2020 in 5 high-volume centers. After 1:1 propensity score matching, a group of patients who underwent RLR was compared with a validation cohort of OLR patients from a high-volume center that did not perform RLR.Main Outcomes and MeasuresA retrospective analysis was performed of prospectively maintained databases at 2 European and 2 US institutions of patients who underwent RLR for HCC between January 1, 2010, and September 30, 2020. The main outcomes were safety and feasibility of RLR for HCC and its oncologic outcomes compared with a European OLR validation cohort. A 2-sided P < .05 was considered significant.ResultsThe study included 398 patients (RLR group: 125 men, 33 women, median [IQR] age, 66 [58-71] years; OLR group: 315 men, 83 women; median [IQR] age, 70 [64-74] years), and 106 RLR patients were compared with 106 OLR patients after propensity score matching. The RLR patients had a significantly longer operative time (median [IQR], 295 [190-370] minutes vs 200 [165-255] minutes, including docking; P < .001) but a significantly shorter hospital length of stay (median [IQR], 4 [3-6] days vs 10 [7-13] days; P < .001) and a lower number of admissions to the intensive care unit (7 [6.6%] vs 21 [19.8%]; P = .002). Incidence of posthepatectomy liver failure was significantly lower in the RLR group (8 [7.5%] vs 30 [28.3%]; P = .001), with no cases of grade C failure. The 90-day overall survival rate was comparable between the 2 groups (RLR, 99.1% [95% CI, 93.5%-99.9%]; OLR, 97.1% [95% CI, 91.3%-99.1%]), as was the cumulative incidence of death related to tumor recurrence (RLR, 8.8% [95% CI, 3.1%-18.3%]; OLR, 10.2% [95% CI, 4.9%-17.7%]).Conclusions and RelevanceThis study represents the largest Western experience to date of full RLR for HCC. Compared with OLR, RLR performed in tertiary centers represents a safe treatment strategy for patients with HCC and those with compromised liver function while achieving oncologic efficacy.
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