On uplifts by warped anti-D3-branes

In this note we outline the arguments against the ten-dimensional consistency of the simplest types of KKLT de Sitter vacua, as given in arXiv:1707.08678. We comment on parametrization proposals within four-dimensional supergravity and express our disagreement with the recent criticism by the authors of arXiv:1808.09428.Comment: Latex, revtex, 4 pages, 1 figure, v2: references added, minor clarification

Passage of radiation through wormholes

We investigate numerically the process of the passage of a radiation pulse through a wormhole and the subsequent evolution of the wormhole that is caused by the gravitational action of this pulse. The initial static wormhole is modeled by the spherically symmetrical Armendariz-Picon solution with zero mass. The radiation pulses are modeled by spherically symmetrical shells of self-gravitating massless scalar fields. We demonstrate that the compact signal propagates through the wormhole and investigate the dynamics of the fields in this process for both cases: collapse of the wormhole into the black hole and for the expanding wormhole.Comment: 18 Pages, 13 figures, minor typos corrected, updated reference

Towards Axion Monodromy Inflation with Warped KK-Modes

We present a particularly simple model of axion monodromy: Our axion is the lowest-lying KK-mode of the RR-2-form-potential $C_2$ in the standard Klebanov-Strassler throat. One can think of this inflaton candidate as being defined by the integral of $C_2$ over the $S^2$ cycle of the throat. It obtains an exponentially small mass from the IR-region in which the $S^2$ shrinks to zero size both with respect to the Planck scale and the mass scale of local modes of the throat. Crucially, the $S^2$ cycle has to be shared between two throats, such that the second locus where the $S^2$ shrinks is also in a warped region. Well-known problems like the potentially dangerous back-reaction of brane/antibrane pairs and explicit supersymmetry breaking are not present in our scenario. However, the inflaton back-reaction starts to deform the geometry strongly once the field excursion approaches the Planck scale. We derive the system of differential equations required to treat this effect quantitatively. Numerical work is required to decide whether back-reaction makes the model suitable for realistic inflation. While we have to leave this crucial issue to future studies, we find it interesting that such a simple and explicit stringy monodromy model allows an originally sub-Planckian axion to go through many periods with full quantitative control before back-reaction becomes strong. Also, the mere existence of our ultra-light throat mode (with double exponentially suppressed mass) is noteworthy.Comment: 28 pages, 3 figures; v2: references added; v3: Corrected an underestimate of supergravity back-reaction in Eq. (36); results changed accordingly; added section 6 which develops the methodology for the 10d non-linear back-reaction; added reference

Oscillatory motion of a droplet in an active poroelastic two-phase model

We investigate flow-driven amoeboid motility as exhibited by microplasmodia of Physarum polycephalum. A poroelastic two-phase model with rigid boundaries is extended to the case of free boundaries and substrate friction. The cytoskeleton is modeled as an active viscoelastic solid permeated by a fluid phase describing the cytosol. A feedback loop between a chemical regulator, active mechanical deformations, and induced flows gives rise to oscillatory and irregular motion accompanied by spatio-temporal contraction patterns. We cover extended parameter regimes of active tension and substrate friction by numerical simulations in one spatial dimension and reproduce experimentally observed oscillation periods and amplitudes. In line with experiments, the model predicts alternating forward and backward ectoplasmatic flow at the boundaries with reversed flow in the center. However, for all cases of periodic and irregular motion, we observe practically no net motion. A simple theoretical argument shows that directed motion is not possible with a spatially independent substrate friction

Development of novel cardiovascular biomarkers by MRI assessment of postprandial physiology

Stress testing is an important concept in cardiovascular medicine. Feeding is a common cardiovascular stressor. Unlike metabolic or immunological stress, the links between feeding-induced haemodynamic stress and cardiovascular risk and dysfunction have not yet been explored in humans. Therefore, cardiovascular responses to a meal were firstly characterised comprehensively in healthy volunteers using a novel rapid MRI protocol. It was shown that the ingestion of food decreased mesenteric vascular resistance substantially, and that this was compensated for by a rise in cardiac output primarily. Previous research demonstrated that mesenteric vasoreactivity was blunted in obese animals and those on a lipid-rich diet. This was linked to greater myocardial mass, an important and independent risk factor for cardiovascular disease in early life. Therefore, the proposed protocol was conducted in adolescents of varying weight to investigate links between mesenteric vasoreactivity and indicators of cardiovascular risk. Blunted postprandial mesenteric vasoreactivity was associated with raised systolic blood pressure and greater left ventricular mass. Importantly, this was independent of other factors known to influence these variables, such as pubertal stage, obesity, insulin resistance, and resting blood pressure. Abnormal vascular resistance of the limbs and the intestine has been described in Fontan-palliated patients with univentricular congenital heart disease, possibly in order to maintain organ perfusion in the presence of low cardiac output and chronic venous congestion. It was hypothesised that this mechanism could interfere with the common cardiovascular responses to feeding. Using the established protocol, vasoconstriction of the legs, but not the intestine, was found in fasting Fontan patients compared to controls. While the mesenteric responses to the meal were similar, Fontan patients had abnormal responses of the celiac axis and the lower limbs

Sasakian quiver gauge theories and instantons on cones over round and squashed seven-spheres

We study quiver gauge theories on the round and squashed seven-spheres, and orbifolds thereof. They arise by imposing $G$-equivariance on the homogeneous space $G/H=\mathrm{SU}(4)/\mathrm{SU}(3)$ endowed with its Sasaki-Einstein structure, and $G/H=\mathrm{Sp}(2)/\mathrm{Sp}(1)$ as a 3-Sasakian manifold. In both cases we describe the equivariance conditions and the resulting quivers. We further study the moduli spaces of instantons on the metric cones over these spaces by using the known description for Hermitian Yang-Mills instantons on Calabi-Yau cones. It is shown that the moduli space of instantons on the hyper-Kahler cone can be described as the intersection of three Hermitian Yang-Mills moduli spaces. We also study moduli spaces of translationally invariant instantons on the metric cone $\mathbb{R}^8/\mathbb{Z}_k$ over $S^7/\mathbb{Z}_k$.Comment: 44 pages; v2: minor changes, reference added; Final version to appear in Nuclear Physics