3,510 research outputs found
On Axionic Field Ranges, Loopholes and the Weak Gravity Conjecture
In this short note we clarify some aspects of the impact that the Weak
Gravity Conjecture has on models of (generalized) natural inflation. We address
in particular certain technical and conceptual concerns recently raised
regarding the stringent constraints and conclusions found in our previous work
(arXiv:1503.04783). We also point out the difficulties faced by attempts to
evade these constraints. These new considerations improve the understanding of
the quantum gravity constraints we found and further support the conclusion
that it remains challenging for axions to drive natural inflation.Comment: 14 page
Fencing in the Swampland: Quantum Gravity Constraints on Large Field Inflation
In this note we show that models of natural inflation based on closed string
axions are incompatible with the weak gravity conjecture (WGC). Specifically,
we use T-duality in order to map the bounds on the charge-to-mass ratio of
particles imposed by the WGC, to constraints on the ratio between instanton
actions and axion decay constants. We use this connection to prove that if the
WGC holds, even when multiple axions are present and mix with each other, one
cannot have large axion decay constants while remaining in a regime of
perturbative control. We also discuss the extension of the WGC to discrete
symmetries and its possible impact on models with axion monodromy, and the
distinction between the strong and mild versions of the WGC. Finally, we offer
some speculations regarding the import of these results to the general theory
of inflation.Comment: 25 page
The temporal binding deficit hypothesis of autism
Frith has argued that people with autism show âweak central coherence,â an unusual bias toward piecemeal rather than configurational processing and a reduction in the normal tendency to process information in context. However, the precise cognitive and neurological mechanisms underlying weak central coherence are still unknown. We propose the hypothesis that the features of autism associated with weak central coherence result from a reduction in the integration of specialized local neural networks in the brain caused by a deficit in temporal binding. The visuoperceptual anomalies associated with weak central coherence may be attributed to a reduction in synchronization of high-frequency gamma activity between local networks processing local features. The failure to utilize context in language processing in autism can be explained in similar terms. Temporal binding deficits could also contribute to executive dysfunction in autism and to some of the deficits in socialization and communication
Cooling of the crust in the neutron star low-mass X-ray binary MXB 1659-29
In quasi-persistent neutron star transients, long outbursts cause the neutron
star crust to be heated out of thermal equilibrium with the rest of the star.
During quiescence, the crust then cools back down. Such crustal cooling has
been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29.
Here we present an additional Chandra observation of MXB 1659-29 in quiescence,
which extends the baseline of monitoring to 6.6 yr after the end of the
outburst. This new observation strongly suggests that the crust has thermally
relaxed, with the temperature remaining consistent over 1000 days. Fitting the
temperature cooling curve with an exponential plus constant model we determine
an e-folding timescale of 465 +/- 25 days, with the crust cooling to a constant
surface temperature of kT = 54 +/- 2 eV (assuming D=10 kpc). From this, we
infer a core temperature in the range 3.5E7-8.3E7 K (assuming D=10 kpc), with
the uncertainty due to the surface composition. Importantly, we tested two
neutron star atmosphere models as well as a blackbody model, and found that the
thermal relaxation time of the crust is independent of the chosen model and the
assumed distance.Comment: accepted for publication in ApJL, 4 pages, 1 figure
Recording the SS Thistlegorm:Rapid multi-image underwater photogrammetric survey of a large Second World War wreck
This paper describes the workflow followed to survey and monitor the interior and exterior of a large and complex metal wreck, the SS Thistlegorm in the Red Sea, using digital photogrammetry. Utilizing a simple single-camera rig and off-the-shelf software, this study presents a cost-effective and easily replicable method for monitoring change in metal wrecks that meets professional standards and can involve non-specialists in data collection. This paper details the background of the SS Thistlegorm, the equipment used, and the photogrammetric surveys conducted in 2017 and 2022. It outlines the importance of having a clearly thought-out data-management system when working on a large target recorded over a limited series of dives. In particular, this paper considers testing the accuracy of the data obtained and describes the post-processing workflow in detail. The conclusion underscores the feasibility of achieving an accurate geo-referenced baseline 3D survey with readily available equipment and how these data can contribute to historical research and ongoing monitoring efforts.</p
- âŚ