Variable quiescent state for the neutron-star X-ray transient SAX J1750.8-2900: not such a hot neutron star after all?

We monitored the neutron star low-mass X-ray binary SAX J1750.8-2900 after the end of its 2015/2016 outburst using the X-ray Telescope (XRT) aboard Swift to detect possible post-outburst 'rebrightenings', similar to those seen after its 2008 outburst. We did not detect any rebrightening behaviour, suggesting that the physical mechanism behind the rebrightening events is not always active after each outburst of the source. Any model attempting to explain these rebrightenings should thus be able to reproduce the different outburst profiles of the source at different times. Surprisingly, our Swift/XRT observations were unable to detect the source, contrary to previous Swift/XRT observations in quiescence. We determined a temperature upper limit of $\leq$ 106 eV, much colder than the post 2008 outburst value of $\sim$ 145 eV. We also report on an archival Chandra observation of the source after its 2011 outburst and found a temperature of $\sim$ 126 eV. These different temperatures, including the non-detection very close after the end of the 2015/2016 outburst, are difficult to explain in any model assuming we observe the cooling emission from a neutron star core or an accretion-heated crust. We discuss our observations in the context of a change in envelope (the outer $\sim$ 100 m of the crust) composition and (possibly in combination with) a cooling crust. Both hypotheses cannot explain our results unless potentially unrealistic assumptions are made. Irrespective of what causes the temperature variability, it is clear that the neutron star in SAX J1750.8-2900 may not be as hot as previously assumed.Comment: Accepted for publication in MNRA

Enhanced Instability of de Sitter Space in Einstein-Gauss-Bonnet Gravity

We show that the addition of a topological Gauss-Bonnet term to the gravitational action can greatly increase the instability of four-dimensional de Sitter space, by favoring the nucleation of black holes. The pair-production rate given by the Euclidean action for the instanton takes the form exp(Delta S) where S is the entropy in Einstein-Gauss-Bonnet theory. The coefficient of the Gauss-Bonnet term in the action sets a stability bound on the curvature of empty de Sitter space. For that coefficient in the low-energy effective action of heterotic string theory, the maximal curvature of de Sitter space is in general much lower than the Planck scale.Comment: 8 page

Swift observations of the dwarf nova ASASSN-18fs

The All Sky Automated Survey for SuperNovae (ASAS-SN) reported a possible Galactic dwarf nova ASASSN-18fs on 2018 March 19 at $\sim$13.2 mag in the V band, with a quiescent magnitude of V$>$17.6. Here we report on the follow-up photometry using the {\it Neil Gehrels Swift Observatory}.Comment: Published by AAS Research Note

Perturbations of vortex ring pairs

We study pairs of co-axial vortex rings starting from the action for a classical bosonic string in a three-form background. We complete earlier work on the phase diagram of classical orbits by explicitly considering the case where the circulations of the two vortex rings are equal and opposite. We then go on to study perturbations, focusing on cases where the relevant four-dimensional transfer matrix splits into two-dimensional blocks. When the circulations of the rings have the same sign, instabilities are mostly limited to wavelengths smaller than a dynamically generated length scale at which single-ring instabilities occur. When the circulations have the opposite sign, larger wavelength instabilities can occur.Comment: 62 pages, 21 figure

Massage Therapy in Outpatient Cancer Care: A Metropolitan Area Analysis.

Massage offers cancer patients general quality of life benefits as well as alleviation of cancer-related symptoms/cancer-treatment-related symptoms including pain, anxiety, and fatigue. Little is known about whether massage is accessible to cancer patients who receive treatment in the outpatient setting and how massage is incorporated into the overall cancer treatment plan. Outpatient cancer centers (n = 78) in a single metropolitan area were included this mixed-methods project that included a systematic analysis of website information and a telephone survey. Massage was offered at only 40 centers (51.3% of total). A range of massage modalities were represented, with energy-based therapies (Reiki and Therapeutic Touch) most frequently provided. Although massage therapists are licensed health care providers in the states included in this analysis, massage was also provided by nurses, physical therapists, and other health care professionals

Segmented strings and the McMillan map

We present new exact solutions describing motions of closed segmented strings in $AdS_3$ in terms of elliptic functions. The existence of analytic expressions is due to the integrability of the classical equations of motion, which in our examples reduce to instances of the McMillan map. We also obtain a discrete evolution rule for the motion in $AdS_3$ of arbitrary bound states of fundamental strings and D1-branes in the test approximation.Comment: 18 page

A window into the neutron star: Modelling the cooling of accretion heated neutron star crusts

In accreting neutron star X-ray transients, the neutron star crust can be substantially heated out of thermal equilibrium with the core during an accretion outburst. The observed subsequent cooling in quiescence (when accretion has halted) offers a unique opportunity to study the structure and thermal properties of the crust. Initially crust cooling modelling studies focussed on transient X-ray binaries with prolonged accretion outbursts (> 1 year) such that the crust would be significantly heated for the cooling to be detectable. Here we present the results of applying a theoretical model to the observed cooling curve after a short accretion outburst of only ~10 weeks. In our study we use the 2010 outburst of the transiently accreting 11 Hz X-ray pulsar in the globular cluster Terzan 5. Observationally it was found that the crust in this source was still hot more than 4 years after the end of its short accretion outburst. From our modelling we found that such a long-lived hot crust implies some unusual crustal properties such as a very low thermal conductivity (> 10 times lower than determined for the other crust cooling sources). In addition, we present our preliminary results of the modelling of the ongoing cooling of the neutron star in MXB 1659-298. This transient X-ray source went back into quiescence in March 2017 after an accretion phase of ~1.8 years. We compare our predictions for the cooling curve after this outburst with the cooling curve of the same source obtained after its previous outburst which ended in 2001.Comment: 4 pages, 1 figure, to appear in the proceedings of "IAUS 337: Pulsar Astrophysics - The Next 50 Years" eds: P. Weltevrede, B.B.P. Perera, L. Levin Preston & S. Sanida

CO2 Emissions reduction strategies and economic development of India

This paper examines the consequences of alternative CO2 emission reduction strategies on economic development and, in particular, the implications for the poor by empirically implementing an economy-wide model for India over a 35-year time horizon. A multi-sectoral, inter-temporal model in the activity analysis framework is used for this purpose. The model with specific technological alternatives, endogenous income distribution, truly dynamic behaviour and covering the whole economy is an integrated top-down bottom-up model. The results show that CO2 emission reduction imposes costs in terms of lower GDP and higher poverty. Cumulative emission reduction targets are, however, preferable to annual reduction targets and that a dynamically optimum strategy can help reduce the burden of emission reductions. The scenarios involving compensation for the loss in welfare are not very encouraging as they require large capital inflows. Contrasted with these, scenarios involving tradable emission quota give India an incentive to be carbon efficient. It becomes a net seller for the first 25 years and because of reduction in carbon intensity it would demand less in later years when it becomes a net buyer. The results suggest that for India, and other developing countries, the window of opportunity to sell carbon quotas is the next two decades or so.

O(N) and O(N) and O(N)

Three related analyses of $\phi^4$ theory with $O(N)$ symmetry are presented. In the first, we review the $O(N)$ model over the $p$-adic numbers and the discrete renormalization group transformations which can be understood as spin blocking in an ultrametric context. We demonstrate the existence of a Wilson-Fisher fixed point using an $\epsilon$ expansion, and we show how to obtain leading order results for the anomalous dimensions of low dimension operators near the fixed point. Along the way, we note an important aspect of ultrametric field theories, which is a non-renormalization theorem for kinetic terms. In the second analysis, we employ large $N$ methods to establish formulas for anomalous dimensions which are valid equally for field theories over the $p$-adic numbers and field theories on $\mathbb{R}^n$. Results for anomalous dimensions agree between the first and second analyses when they can be meaningfully compared. In the third analysis, we consider higher derivative versions of the $O(N)$ model on $\mathbb{R}^n$, the simplest of which has been studied in connection with spatially modulated phases. Our general formula for anomalous dimensions can still be applied. Analogies with two-derivative theories hint at the existence of some interesting unconventional field theories in four real Euclidean dimensions.Comment: 44 pages, 8 figure