Solving the Effective Field Equations for the Newtonian Potential

Loop corrections to the gravitational potential are usually inferred from scattering amplitudes, which seems quite different from how the linearized Einstein equations are solved with a static, point mass to give the classical potential. In this study we show how the Schwinger-Keldysh effective field equations can be used to compute loop corrections to the potential in a way which parallels the classical treatment. We derive explicit results for the one loop correction from the graviton self-energy induced by a massless, minimally coupled scalar.Comment: 15 pages, uses LaTeX2

Stress Tensor Correlators in the Schwinger-Keldysh Formalism

We express stress tensor correlators using the Schwinger-Keldysh formalism. The absence of off-diagonal counterterms in this formalism ensures that the +- and -+ correlators are free of primitive divergences. We use dimensional regularization in position space to explicitly check this at one loop order for a massless scalar on a flat space background. We use the same procedure to show that the ++ correlator contains the divergences first computed by `t Hooft and Veltman for the scalar contribution to the graviton self-energy.Comment: 14 pages, LaTeX 2epsilon, no figures, revised for publicatio

Possible Enhancement of High Frequency Gravitational Waves

We study the tensor perturbations in a class of non-local, purely gravitational models which naturally end inflation in a distinctive phase of oscillations with slight and short violations of the weak energy condition. We find the usual generic form for the tensor power spectrum. The presence of the oscillatory phase leads to an enhancement of gravitational waves with frequencies somewhat less than 10^{10} Hz.Comment: 27 pages, 11 figures, LaTeX.2

PD effluent specimen collection: your questions answered

When a patient on peritoneal dialysis (PD) presents with suspected PD-related peritonitis (e.g. cloudy PD fluid and abdominal pain), one of the most important initial aspects of management is for the nephrology nurse/home dialysis nurse to collect PD effluent specimens for white blood cells count, Gram stain, culture and sensitivity for inspection and to send for laboratory testing before antibiotics are started. A review by seven members of the International Society for Peritoneal Dialysis (ISPD) Nursing Committee of all 133 questions posted to the ISPD website ‘Questions about PD’ over the last 4 years (January 2018–December 2021), revealed 97 posted by nephrology nurses from around the world. Of these 97 questions, 10 were noted to be related to best practices for PD effluent specimen collection. For our review, we focused on these 10 questions along with their responses by the members of the ISPD ‘Ask The Experts Team’, whereby existing best practice recommendations were considered, if available, relevant literature was cited and differences in international practice discussed. We revised the original responses for clarity and updated the references. We found that these 10 questions were quite varied but could be organised into four categories: how to collect PD effluent safely; how to proceed with PD effluent collection; how to collect PD effluent for assessment; and how to proceed with follow-up PD effluent collection after intraperitoneal antibiotics have been started. In general, we found that there was limited evidence in the PD literature to answer several of these 10 questions posted to the ISPD website ‘Questions about PD’ by nephrology nurses from around the world on this important clinical topic of best practices for PD effluent specimen collection. Some of these questions were also not addressed in the latest ISPD Peritonitis Guidelines. Moreover, when polling members of our ISPD Nursing Committee we found when answering a few of these questions, nursing practice varied within and among countries. We encourage PD nurses to conduct their own research on this important topic, focusing on areas where research evidence is lacking

Loop Corrections to Cosmological Perturbations in Multi-field Inflationary Models

We investigate one-loop quantum corrections to the power spectrum of adiabatic perturbation from entropy modes/adiabatic mode cross-interactions in multiple DBI inflationary models. We find that due to the non-canonical kinetic term in DBI models, the loop corrections are enhanced by slow-varying parameter $\epsilon$ and small sound speed $c_s$. Thus, in general the loop-corrections in multi-DBI models can be large. Moreover, we find that the loop-corrections from adiabatic/entropy cross-interaction vertices are IR finite.Comment: 21 pages, 7 figures; v2, typos corrected, ref added; v3 typos corrected, version for publishing in jca

Super-Hubble de Sitter Fluctuations and the Dynamical RG

Perturbative corrections to correlation functions for interacting theories in de Sitter spacetime often grow secularly with time, due to the properties of fluctuations on super-Hubble scales. This growth can lead to a breakdown of perturbation theory at late times. We argue that Dynamical Renormalization Group (DRG) techniques provide a convenient framework for interpreting and resumming these secularly growing terms. In the case of a massless scalar field in de Sitter with quartic self-interaction, the resummed result is also less singular in the infrared, in precisely the manner expected if a dynamical mass is generated. We compare this improved infrared behavior with large-N expansions when applicable.Comment: 33 pages, 4 figure

Hessence: A New View of Quintom Dark Energy

Recently a lot of attention has been drawn to build dark energy model in which the equation-of-state parameter $w$ can cross the phantom divide $w=-1$. One of models to realize crossing the phantom divide is called quintom model, in which two real scalar fields appears, one is a normal scalar field and the other is a phantom-type scalar field. In this paper we propose a non-canonical complex scalar field as the dark energy, which we dub ``hessence'', to implement crossing the phantom divide, in a similar sense as the quintom dark energy model. In the hessence model, the dark energy is described by a single field with an internal degree of freedom rather than two independent real scalar fields. However, the hessence is different from an ordinary complex scalar field, we show that the hessence can avoid the difficulty of the Q-balls formation which gives trouble to the spintessence model (An ordinary complex scalar field acts as the dark energy). Furthermore, we find that, by choosing a proper potential, the hessence could correspond to a Chaplygin gas at late times.Comment: Latex2e, 12 pages, no figure; v2: discussions and references added, 14 pages, 3 eps figures; v3: published versio

One-loop corrections to a scalar field during inflation

The leading quantum correction to the power spectrum of a gravitationally-coupled light scalar field is calculated, assuming that it is generated during a phase of single-field, slow-roll inflation.Comment: 33 pages, uses feynmp.sty and ioplatex journal style. v2: matches version published in JCAP. v3: corrects sign error in Eq. (58). Corrects final coefficient of the logarithm in Eq. (105). Small corrections to discussion of divergences in 1-point function. Minor improvements to discussion of UV behaviour in Sec. 4.

One-loop corrections to the curvature perturbation from inflation

An estimate of the one-loop correction to the power spectrum of the primordial curvature perturbation is given, assuming it is generated during a phase of single-field, slow-roll inflation. The loop correction splits into two parts, which can be calculated separately: a purely quantum-mechanical contribution which is generated from the interference among quantized field modes around the time when they cross the horizon, and a classical contribution which comes from integrating the effect of field modes which have already passed far beyond the horizon. The loop correction contains logarithms which may invalidate the use of naive perturbation theory for cosmic microwave background (CMB) predictions when the scale associated with the CMB is exponentially different from the scale at which the fundamental theory which governs inflation is formulated.Comment: 28 pages, uses feynmp.sty and ioplatex journal style. v2: supersedes version published in JCAP. Some corrections and refinements to the discussion and conclusions. v3: Corrects misidentification of quantum correction with an IR effect. Improvements to the discussio

Classical approximation to quantum cosmological correlations

We investigate up to which order quantum effects can be neglected in calculating cosmological correlation functions after horizon exit. As a toy model, we study $\phi^3$ theory on a de Sitter background for a massless minimally coupled scalar field $\phi$. We find that for tree level and one loop contributions in the quantum theory, a good classical approximation can be constructed, but for higher loop corrections this is in general not expected to be possible. The reason is that loop corrections get non-negligible contributions from loop momenta with magnitude up to the Hubble scale H, at which scale classical physics is not expected to be a good approximation to the quantum theory. An explicit calculation of the one loop correction to the two point function, supports the argument that contributions from loop momenta of scale $H$ are not negligible. Generalization of the arguments for the toy model to derivative interactions and the curvature perturbation leads to the conclusion that the leading orders of non-Gaussian effects generated after horizon exit, can be approximated quite well by classical methods. Furthermore we compare with a theorem by Weinberg. We find that growing loop corrections after horizon exit are not excluded, even in single field inflation.Comment: 44 pages, 1 figure; v2: corrected errors, added references, conclusions unchanged; v3: added section in which we compare with stochastic approach; this version matches published versio