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Search Results: 1 - 10 of 4769 matches for " Yuko Tanaka "
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Influence on observation from IR divergence during inflation -- Single field inflation --
Yuko Urakawa,Takahiro Tanaka
Physics , 2009, DOI: 10.1143/PTP.122.779
Abstract: A naive computation of the correlation functions of fluctuations generated during inflation suffers from logarithmic divergences in the infrared (IR) limit. In this paper, we propose one way to solve this IR divergence problem in the single-field inflation model. The key observation is that the variables that are commonly used in describing fluctuations are influenced by what we cannot observe. Introducing a new perturbation variable which mimics what we actually observe, we propose a new prescription to solve the time evolution of perturbation in which this leakage of information from the unobservable region of the universe is shut off. We give a proof that IR divergences are absent as long as we follow this new scheme. We also show that the secular growth of the amplitude of perturbation is also suppressed, at least, unless very higher order perturbation is discussed.
Influence on observation from IR divergence during inflation -- Multi field inflation --
Yuko Urakawa,Takahiro Tanaka
Physics , 2009, DOI: 10.1143/PTP.122.1207
Abstract: We propose one way to regularize the fluctuations generated during inflation, whose infrared (IR) corrections diverge logarithmically. In the case of a single field inflation model, recently, we proposed one solution to the IR divergence problem. There, we introduced new perturbative variables which better mimic actual observable fluctuations, and proved the regularity of correlation functions with respect to these variables. In this paper, we extend our previous discussions to a multi field inflation model. We show that, as long as we consider the case that the non-linear interaction acts for a finite duration, observable fluctuations are free from IR divergences in the multi field model, too. In contrast to the single field model, to discuss observables, we need to take into account the effects of quantum decoherence which pick up a unique history of the universe from various possibilities contained in initial quantum state set naturally in the early stage of the universe.
Strong restriction on inflationary vacua from the local gauge invariance III: Infrared regularity of graviton loops
Takahiro Tanaka,Yuko Urakawa
Physics , 2014, DOI: 10.1093/ptep/ptu071
Abstract: It has been claimed that the super Hubble modes of the graviton generated during inflation can make loop corrections diverge. Even if we introduce an infrared (IR) cutoff at a comoving scale as an ad hoc but a practical way for the regularization, we encounter the secular growth, which may lead to the breakdown of perturbative expansion for a sufficiently long lasting inflation. In this paper, we show that the IR pathology concerning the graviton can be attributed to the presence of residual gauge degrees of freedom in the local observable universe as in the case of the adiabatic curvature perturbation. We will show that choosing the Euclidean vacuum as the initial state ensures the invariance under the above-mentioned residual gauge transformations. We will also show that as long as we consider a gauge invariant quantity in the local universe, we encounter neither the IR divergence nor the secular growth. The argument in this paper applies to general single field models of inflation up to a sufficiently high order in perturbation.
IR divergence does not affect the gauge-invariant curvature perturbation
Yuko Urakawa,Takahiro Tanaka
Physics , 2010, DOI: 10.1103/PhysRevD.82.121301
Abstract: We address the infrared(IR) divergence problem during inflation that appears in the loop corrections to the primordial perturbations. In our previous paper, we claimed that, at least in single field models, the IR divergence is originating from the gauge artifact. Namely, diverging IR corrections should not appear in genuine gauge-invariant observables. We propose here one simple but explicit example of such gauge-invariant quantities. Then, we explicitly calculate such a quantity to find that the IR divergence is absent at the leading order in the slow-roll approximation for the usual scale invariant vacuum state. At the same time we notice that there is a subtle issue on the gauge-invariance in how to specify the initial vacuum state.
Natural selection of inflationary vacuum required by infra-red regularity and gauge-invariance
Yuko Urakawa,Takahiro Tanaka
Physics , 2010, DOI: 10.1143/PTP.125.1067
Abstract: It has been an issue of debate whether the inflationary infrared(IR) divergences are physical or not. Our claim is that, at least, in single-field models, the answer is "No," and that the spurious IR divergence is originating from the careless treatment of the gauge modes. In our previous work we have explicitly shown that the IR divergence is absent in the genuine gauge-invariant quantity at the leading order in the slow-roll approximation. We extend our argument to include higher-order slow-roll corrections and the contributions from the gravitational waves. The key issue is to assure the gauge invariance in the choice of the initial vacuum, which is a new concept that has not been considered in conventional calculations.
Dominance of gauge artifact in the consistency relation for the primordial bispectrum
Takahiro Tanaka,Yuko Urakawa
Physics , 2011, DOI: 10.1088/1475-7516/2011/05/014
Abstract: The conventional cosmological perturbation theory has been performed under the assumption that we know the whole spatial region of the universe with infinite volume. This is, however, not the case in the actual observations because observable portion of the universe is limited. To give a theoretical prediction to the observable fluctuations, gauge-invariant observables should be composed of the information in our local observable universe with finite volume. From this point of view, we reexamine the primordial non-Gaussianity in single field models, focusing on the bispectrum in the squeezed limit. A conventional prediction states that the bispectrum in this limit is related to the power spectrum through the so-called consistency relation. However, it turns out that, if we adopt a genuine gauge invariant variable which is naturally composed purely of the information in our local universe, the leading term for the bispectrum in the squeezed limit predicted by the consistency relation vanishes.
Loops in inflationary correlation functions
Takahiro Tanaka,Yuko Urakawa
Physics , 2013, DOI: 10.1088/0264-9381/30/23/233001
Abstract: We review the recent progress regarding the loop corrections to the correlation functions in the inflationary universe. A naive perturbation theory predicts that loop corrections generated during inflation suffer from various infrared (IR) pathologies. Introducing an IR cutoff by hand is not only unsatisfactory but also does not fix the problem of secular growth, which may ruin the predictive power of inflation models if the inflation lasts sufficiently long. We discuss the origin of the IR divergences and explore the regularity conditions of loop corrections for the adiabatic perturbation, the iso-curvature perturbation, and the tensor perturbation, in turn. These three kinds of perturbations have qualitative differences, but in discussing the IR regularity there is a feature common to all cases, which is the importance of the proper identification of observable quantities. Genuinely observable quantities should respect the gauge invariance from the view point of a local observer. Interestingly, we find that the requirement of the IR regularity restricts the allowed quantum states.
Strong restriction on inflationary vacua from the local gauge invariance I: Local gauge invariance and infrared regularity
Takahiro Tanaka,Yuko Urakawa
Physics , 2012,
Abstract: The primordial perturbation is widely accepted to be generated through the vacuum fluctuation of the scalar field which drives inflation. It is, however, not completely clear what is the natural vacuum in the inflationary universe particularly in the presence of non-linear interactions. In this series of papers, we will address this issue, focusing on the condition required for the removal of the divergence from the infrared (IR) contribution to loop diagrams. We show that requesting the gauge invariance in the local observable universe guarantees the IR regularity of the loop corrections beginning with a simple initial state. In our previous works, the IR regularity condition was discussed using the slow roll expansion, which restricts the background evolution of the inflationary universe. We will show more generally that requesting the gauge invariance/the IR regularity leads to non-trivial constraints on the allowed quantum states.
Strong restriction on inflationary vacua from the local gauge invariance II: Infrared regularity and absence of the secular growth in Euclidean vacuum
Takahiro Tanaka,Yuko Urakawa
Physics , 2013,
Abstract: We investigate the initial state of the inflationary universe. In our recent publications, we showed that requesting the gauge invariance in the local observable universe to the initial state guarantees the infrared (IR) regularity of loop corrections in a general single clock inflation. Following this study, in this paper, we show that choosing the Euclidean vacuum ensures the gauge invariance in the local universe and hence the IR regularity of loop corrections. It has been suggested that loop corrections to inflationary perturbations may yield the secular growth, which can lead to the break down of the perturbative analysis in an extremely long term inflation. The absence of the secular growth has been claimed by picking up only the IR contributions, which we think is incomplete because the non-IR modes which are comparable to or smaller than the Hubble scale potentially can contribute to the secular growth. We prove the absence of the secular growth without neglecting these non-IR modes to a certain order in the perturbative expansion. We also discuss how the regularity of the n-point functions for the genuinely gauge invariant variable constrains the initial states of the inflationary universe. These results apply in a fully general single field model of inflation.
High Preoperative Anxiety Level and the Risk of Intraoperative Hypothermia  [PDF]
Noriyoshi Tanaka, Yuko Ohno, Megumi Hori, Mai Utada, Kenji Ito, Toshiyasu Suzuki
International Journal of Clinical Medicine (IJCM) , 2012, DOI: 10.4236/ijcm.2012.36085
Abstract: Aim: The relationship between preoperative anxiety level and intraoperative hypothermia (<36℃) was investigated. Background: Core temperature often decreases during surgery, with an initial rapid decrease followed by a slower decrease for about 2 hours. Preoperative anxiety may influence perioperative physiological responses. The relationship between preoperative anxiety level and perioperative decrease in core temperature has not been studied closely. Design: A prospective observational study. Methods: This study enrolled 120 adult patients who underwent elective major abdominal surgery under combined epidural and general anesthesia. Tympanic membrane temperature was used to measure core temperature preoperatively and during the operation. The relationship between anxiety level according to the State-Trait Anxiety Inventory (STAI) and core temperature was examined using descriptive and multivariate risk analysis. Results: High anxiety level was found in 61 patients (51%), of which 26 (43%) developed hypothermia during the first hour and 40 (66%) developed hypothermia during the first 2 hours of anesthesia. After adjustment for covariates, patients with a high anxiety level were found to have a 2.17-fold higher risk of hypothermia during the first hour and a 1.77-fold higher risk of hypothermia during the first 2 hours than patients with a low/moderate anxiety level. Conclusions: The risk of hypothermia in the early phase of general anesthesia can be predicted by measurement of the preoperative anxiety level using the STAI. Relevance to Clinical Practice: Patients with a high anxiety level had a significantly higher risk of intraoperative hypothermia. Preoperative preventive nursing care programs should include anxiety management and thermal care.
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