Covariant path integrals for quantum fields back-reacting on classical space-time

We introduce configuration space path integrals for quantum fields interacting with classical fields. We show that this can be done consistently by proving that the dynamics are completely positive directly, without resorting to master equation methods. These path integrals allow one to readily impose space-time symmetries, including Lorentz invariance or diffeomorphism invariance. They generalize and combine the Feynman-Vernon path integral of open quantum systems and the stochastic path integral of classical stochastic dynamics while respecting symmetry principles. We introduce a path integral formulation of general relativity where the space-time metric is treated classically, as well as a diffeomorphism invariant theory based on the trace of Einstein's equations. The theory is a candidate for a fundamental theory that reconciles general relativity with quantum mechanics.Comment: 9 main, 4 appendice

The constraints of post-quantum classical gravity

We study a class of theories in which space-time is treated classically, while interacting with quantum fields. These circumvent various no-go theorems and the pathologies of semi-classical gravity, by being linear in the density matrix and stochastic on the classical phase-space. The theory can either be considered fundamental or an effective theory where the classical limit is taken of space-time. The theories have the dynamics of general relativity as their classical limit and provide a way to study the back-action of quantum fields on the space-time metric. Here, we provide a methadology to derive the constraint equations of such a theory by imposing invariance of the dynamics under time-reparametrization invariance. This leads to generalisations of the Hamiltonian and momentum constraints, and we compute their algebra for the case of a quantum scalar field interacting with gravity.Comment: 21 pages, comments welcom

Diffeomorphism invariant classical-quantum path integrals for Nordstrom gravity

When classical degrees of freedom and quantum degrees of freedom are consistently coupled, the former diffuse, while the latter undergo decoherence. Here, we construct a theory of quantum matter fields and Nordstrom gravity in which the space-time metric is treated classically. The dynamics is constructed via the classical-quantum path integral and is completely positive, trace preserving (CPTP), and respects the classical-quantum split. The weak field limit of the model matches the Newtonian limit of the full covariant path integral but it is easier to show that the theory is both diffeomorphism invariant, CPTP, and has the appropriate classical limit

Stellenwert der Verlaufsbeobachtung, operativen Tumorresektion und Monochemotherapie bei Oligodendrogliomen WHO Grad II

INTRODUCTION Gliomas of histological WHO grades 2 and 3 show a heterogenous prognosis that largely depends on molecular tumor characteristics. Presence of 1p/19q codeletions distinguishes oligodendroglioma from astrocytoma among IDHmut gliomas. Both entities are associated with favourable outcome when compared to IDHwt WHO grade 2 and 3 astrocytomas with molecular features of glioblastomas, e.g., pTERTmut (which are now referred as glioblastoma). We here investigated different therapies in WHO grade 2 oligodendrogliomas (Publication I) and assessed clinical and epigenetic similarities between IDHwt pTERTmut WHO grade 2 and 3 astrocytomas and glioblastoma (Publication II). METHODS In this single-centre, retrospective study, 420 patients were included, including 142 patients with oligodendroglioma, 54 patients with IDHwt astrocytoma WHO grade 2 or 3 with pTERTmut and 224 patients with histopathological glioblastoma. In Publication I, different therapeutic approaches in the treatment of oligodendroglioma WHO grade 2 were investigated, including surveillance strategies after biopsy (wait-and-scan; n=59) or tumor resection (n=27), temozolomide chemotherapy after biopsy (n=26) or the combination therapy of procarbazine, CCNU/lomustine and vincristine (PCV; n=30) after biopsy. In Publication II, extent and pattern of MGMT promoter methylation in IDHwt pTERTmut astrocytomas WHO grade 2 and 3 and in histological glioblastoma were investigated through PCR and Sanger sequencing. RESULTS The retrospective outcome analysis of WHO grade 2 oligodendrogliomas showed superior progression-free survival in patients receiving PCV therapy after biopsy when compared to wait-and-scan or resection only or temozolomide. (in years, 9.1 (PCV) vs 5.1 (wait-and-scan) vs 4.4 (resection) vs 3.6 (temozolomide); p=0.05). Longer progression-free survival in patients treated with PCV when compared to temozolomide was also seen in a matched-pair analysis (p=0.03) and in patients that were treated with PCV or temozolomide at first progression (p=0.04). Histological progression occurred at significantly lower rate in the PCV cohort when compared to all other cohorts (p=0.01). Epigenetic analyses of the MGMT promoter showed similar pattern and extent of methylation in IDHwt pTERTmut astrocytomas and glioblastomas. Overall survival and progression-free survival were similar in both groups irrespective of lower initial histological grade. CONCLUSION PCV chemotherapy prolongs progression-free survival and potentially delays malignant transformation in oligodendroglioma WHO grade 2. Extent and pattern of MGMT promoter methylation in IDHwt pTERTmut astrocytomas and glioblastomas are similar

Gravitationally induced decoherence vs space-time diffusion: testing the quantum nature of gravity

We consider two interacting systems when one is treated classically while the other system remains quantum. Consistent dynamics of this coupling has been shown to exist, and explored in the context of treating space-time classically. Here, we prove that any such hybrid dynamics necessarily results in decoherence of the quantum system, and a breakdown in predictability in the classical phase space. We further prove that a trade-off between the rate of this decoherence and the degree of diffusion induced in the classical system is a general feature of all classical quantum dynamics; long coherence times require strong diffusion in phase-space relative to the strength of the coupling. Applying the trade-off relation to gravity, we find a relationship between the strength of gravitationally-induced decoherence versus diffusion of the metric and its conjugate momenta. This provides an experimental signature of theories in which gravity is fundamentally classical. Bounds on decoherence rates arising from current interferometry experiments, combined with precision measurements of mass, place significant restrictions on theories where Einstein’s classical theory of gravity interacts with quantum matter. We find that part of the parameter space of such theories are already squeezed out, and provide figures of merit which can be used in future mass measurements and interference experiments

Objective trajectories in hybrid classical-quantum dynamics

Consistent dynamics which couples classical and quantum degrees of freedom exists, provided it is stochastic. This provides a way to study the back-reaction of quantum fields on space-time which does not suffer from the pathologies of the semi-classical equations. Here we introduce several toy models in which to study hybrid classical-quantum evolution, including a qubit coupled to a particle in a potential, and a quantum harmonic oscillator coupled to a classical one. We present an unravelling approach to calculate the dynamics. Unlike the purely quantum case, the trajectories (or histories) of this unravelling can be unique, conditioned on the classical degrees of freedom. This provides a potential solution to the "measurement problem" of quantum theory; quantum systems become classical because they interact with a genuinely classical field.Comment: Main text: 24 pages, 8 figures; appendix 6 page

The weak field limit of quantum matter back-reacting on classical spacetime

Consistent coupling of quantum and classical degrees of freedom exists so long as there is both diffusion of the classical degrees of freedom and decoherence of the quantum system. In this paper, we derive the Newtonian limit of such classical-quantum (CQ) theories of gravity. Our results are obtained both via the gauge fixing of the recently proposed path integral theory of CQ general relativity and via the CQ master equation approach. In each case, we find the same weak field dynamics. We find that the Newtonian potential diffuses by an amount lower bounded by the decoherence rate into mass eigenstates. We also present our results as an unravelled system of stochastic differential equations for the trajectory of the hybrid classical-quantum state and provide a series of kernels for constructing figures of merit, which can be used to rule out part of the parameter space of classical-quantum theories of gravity by experimentally testing it via the decoherence-diffusion trade-off. We compare and contrast the weak field limit to previous models of classical Newtonian gravity coupled to quantum systems. Here, we find that the Newtonian potential and quantum state change in lock-step, with the flow of time being stochastic.Comment: 42 pages, 1 table, comments welcome

PCV chemotherapy alone for WHO grade 2 oligodendroglioma: prolonged disease control with low risk of malignant progression

INTRODUCTION The role of chemotherapy alone in newly diagnosed WHO grade 2 oligodendroglioma after biopsy, incomplete or gross total resection remains controversial. We here analyze the clinical outcome of four patient cohorts being treated with either procarbazine, CCNU and vincristine (PCV) or temozolomide (TMZ) after biopsy, resection only, or wait-and-scan after biopsy. METHODS Patients (n = 142) with molecularly defined oligodendroglioma (WHO 2016) were assigned to four cohorts: W&S, wait-and-scan after stereotactic biopsy (n = 59); RES, surgical resection only (n = 27); TMZ, temozolomide after biopsy (n = 26) or PCV (n = 30) after biopsy. Presurgical MRI T2 tumor volumes were obtained by manual segmentation. Progression-free survival (PFS), post-recurrence PFS (PR-PFS) and rate of histological progression to grade 3 were analyzed. RESULTS PFS was longest after PCV (9.1 years), compared to 5.1 years after W&S, 4.4 years after RES and 3.6 years after TMZ. The rate of histological progression from grade 2 to 3 within 10 years was 9% for the PCV, 29% for the W&S, 67% for the RES and 75% for the TMZ group (p = 0.01). In the W&S group, patients treated with PCV at first relapse had a longer PFS from intervention than those treated with TMZ (7.2 vs 4.0 years, p = 0.04). Multivariate analysis identified smaller tumor volume prior to any intervention (p = 0.02) to be prognostic for PFS. CONCLUSIONS PCV chemotherapy alone is an effective treatment for WHO grade 2 oligodendroglioma, with long PFS and low rate of histological progression

A surface mooring for air–sea interaction research in the Gulf Stream. Part I : mooring design and instrumentation

Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 29 (2012): 1363–1376, doi:10.1175/JTECH-D-12-00060.1.The design of a surface mooring for deployment in the Gulf Stream in the Mid-Atlantic Bight is described. The authors' goals were to observe the surface meteorology; upper-ocean variability; and air–sea exchanges of heat, freshwater, and momentum in and near the Gulf Stream during two successive 1-yr deployments. Of particular interest was quantifying these air–sea fluxes during wintertime events that carry cold, dry air from the land over the Gulf Stream. Historical current data and information about the surface waves were used to guide the design of the surface mooring. The surface buoy provided the platform for both bulk meteorological sensors and a direct covariance flux system. Redundancy in the meteorological sensors proved to be a largely successful strategy to obtain complete time series. Oceanographic instrumentation was limited in size by considerations of drag; and two current meters, three temperature–salinity recorders, and 15 temperature recorders were deployed. Deployment from a single-screw vessel in the Gulf Stream required a controlled-drift stern first over the anchor sites. The first deployment lasted the planned full year. The second deployment ended after 3 months when the mooring was cut by unknown means at a depth of about 3000 m. The mooring was at times in the core of the Gulf Stream, and a peak surface current of over 2.7 m s−1 was observed. The 15-month records of surface meteorology and air–sea fluxes captured the seasonal variability as well as several cold-air outbreaks; the peak observed heat loss was in excess of 1400 W m−2.This work was funded by the National Science Foundation Grant OCE04-24536 as part of the CLIVAR Mode Water Dynamics Experiment (CLIMODE). The Vetlesen Foundation is also acknowledged for the early support of SB.2013-03-0