Quantum Creation of the Randall-Sundrum Bubble

We investigate the semiclassical instability of the Randall-Sundrum brane world. We carefully analyze the bubble solution with the Randall-Sundrum background, which expresses the decay of the brane world. We evaluate the decay probability following the Euclidean path integral approach to quantum gravity. Since a bubble rapidly expands after the nucleation, the entire spacetime will be occupied by such bubbles.Comment: 13 pages, 6 figures, To appear in Prog. Theor. Phy

Thermal evolution and lifetime of intrinsic magnetic fields of Super Earths in habitable zones

We have numerically studied the thermal evolution of various-mass terrestrial planets in habitable zones, focusing on duration of dynamo activity to generate their intrinsic magnetic fields, which may be one of key factors in habitability on the planets. In particular, we are concerned with super-Earths, observations of which are rapidly developing. We calculated evolution of temperature distributions in planetary interior, using Vinet equations of state, Arrhenius-type formula for mantle viscosity, and the astrophysical mixing length theory for convective heat transfer modified for mantle convection. After calibrating the model with terrestrial planets in the Solar system, we apply it for 0.1--$10M_{\oplus}$ rocky planets with surface temperature of 300~\mbox{K} (in habitable zones) and the Earth-like compositions. With the criterion for heat flux at the CMB (core-mantle boundary), the lifetime of the magnetic fields is evaluated from the calculated thermal evolution. We found that the lifetime slowly increases with the planetary mass ($M_p$) independent of initial temperature gap at the core-mantle boundary ($\Delta T_{\rm CMB}$) but beyond a critical value $M_{c,p}$ ($\sim O(1)M_{\oplus}$) it abruptly declines by the mantle viscosity enhancement due to the pressure effect. We derived $M_{c,p}$ as a function of $\Delta T_{\rm CMB}$ and a rheological parameter (activation volume, $V^*$). Thus, the magnetic field lifetime of super-Earths with $M_p > M_{p,c}$ sensitively depends on $\Delta T_{\rm CMB}$, which reflects planetary accretion, and $V^*$, which has uncertainty at very high pressure. More advanced high-pressure experiments and first-principle simulation as well as planetary accretion simulation are needed to discuss habitability of super-Earths.Comment: 19pages, 15 figures, accepted for publication in Ap

3D MHD Simulations of Planet Migration in Turbulent Stratified Disks

We performed 3D MHD simulations of planet migration in stratified disks using the Godunov code PLUTO, where the disk is turbulent due to the magnetorotational instability. We study the migration for planets with different planet-star mass ratios $q=M_{p}/M_{s}$. In agreement with previous studies, for the low-mass planet cases ($q=5\times10^{-6}$ and $10^{-5}$), migration is dominated by random fluctuations in the torque. For a Jupiter-mass planet $(q=M_{p}/M_{s}=10^{-3}$ for $M_{s}=1M_{\odot})$, we find a reduction of the magnetic stress inside the orbit of the planet and around the gap region. After an initial stage where the torque on the planet is positive, it reverses and we recover migration rates similar to those found in disks where the turbulent viscosity is modelled by an $\alpha$ viscosity. For the intermediate-mass planets ($q=5\times10^{-5}, 10^{-4}$ and $2\times10^{-4}$) we find a new and so far unexpected behavior. In some cases they experience sustained and systematic outwards migration for the entire duration of the simulation. For this case, the horseshoe region is resolved and torques coming from the corotation region can remain unsaturated due to the stresses in the disk. These stresses are generated directly by the magnetic field. The magnitude of the horseshoe drag can overcome the negative Lindblad contribution when the local surface density profile is flat or increasing outwards, which we see in certain locations in our simulations due to the presence of a zonal flow. The intermediate-mass planet is migrating radially outwards in locations where there is a positive gradient of a pressure bump (zonal flow).Comment: Accepted for publication in Ap

Augmented Cardiopulmonary Baroreflex Sensitivity in Intradialytic Hypertension.

IntroductionEnd-stage renal disease (ESRD) patients with a paradoxical increase in blood pressure (BP) during hemodialysis (HD), termed intradialytic hypertension (ID-HTN), are at significantly increased risk for mortality and adverse cardiovascular events. ID-HTN affects up to 15% of all HD patients, and the pathophysiologic mechanisms remain unknown. We hypothesized that ESRD patients prone to ID-HTN have heightened volume-sensitive cardiopulmonary baroreflex sensitivity (BRS) that leads to exaggerated increases in sympathetic nervous system (SNS) activation during HD.MethodsWe studied ESRD patients on maintenance HD with ID-HTN (n = 10) and without ID-HTN (controls, n = 12) on an interdialytic day, 24 to 30 hours after their last HD session. We measured continuous muscle sympathetic nerve activity (MSNA), beat-to-beat arterial BP, and electrocardiography (ECG) at baseline, and during graded lower body negative pressure (LBNP). Low-dose LBNP isolates cardiopulmonary BRS, whereas higher doses allow assessment of physiologic responses to orthostatic stress.ResultsThe ID-HTN patients had significantly higher pre- and post-HD BP, and greater interdialytic fluid weight gain compared to controls. There was a significantly greater increase in MSNA burst incidence (P = 0.044) during graded LBNP in the ID-HTN group, suggesting heightened cardiopulmonary BRS. The ID-HTN group also had a trend toward increased diastolic BP response during LBNP, and had significantly greater increases in BP during the cold pressor test.ConclusionPatients with ID-HTN have augmented cardiopulmonary BRS that may contribute to increased SNS activation and BP response during HD