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Robert S Thorne

Publications and source records attributed to Robert S Thorne.

3 recordsLinked to original sources
arXiv2020

Inferring the effective fraction of the population infected with Covid-19 from the behaviour of Lombardy, Madrid and London relative to the remainder of Italy, Spain and England

I use a very simple deterministic model for the spread of Covid-19 in a large population. Using this to compare the relative decay of the number of deaths per day between different regions in Italy, Spain and England, each applying in principle the same social distancing procedures across the whole country, I obtain an estimate of the total fraction of the population which had already become infected by April 10th. In the most heavily affected regions, Lombardy, Madrid and London, this fraction is higher than expected, i.e. $\approx 0.3$. This result can then be converted to a determination of the infection fatality rate $ifr$, which appears to be $ifr \approx 0.0025-0.005$, and even smaller in London, somewhat lower than usually assumed. Alternatively, the result can also be interpreted as an effectively larger fraction of the population than simple counting would suggest if there is a variation in susceptibility to infection with a variance of up to a value of about 2. The implications are very similar for either interpretation or for a combination of effects.

q-bio.PE↗
arXiv2013

Theoretical Procedures and the effect on PDFs and $α_S(M_Z^2)$

I consider the effect on partons distribution functions (PDFs) of changes in the theoretical procedure used in a PDF fit. I consider using the 3-flavour fixed flavour number scheme instead of the standard general mass variable flavour number scheme used in the MSTW analysis. This results in the light quarks increasing at most $x$ values, the gluon distribution becoming softer at high values of $x$ and larger at small $x$, and the coupling constant $α_S(M_Z^2)$ falling, particularly at NNLO. The fit quality also deteriorates.I also consider lowering the kinematic cut on $W^2$ for DIS data and introducing higher twist terms which are fit to data. This results in much smaller effects on both PDFs and $α_S(M_Z^2)$, with changes generally smaller than uncertainties, except for quarks at very high $x$. I show that the fixed flavour scheme and variable flavour scheme structure functions differ significantly for $x \sim 0.01$ at high $Q^2$. I demonstrate that in the fixed flavour scheme there is a slow convergence of large logarithmic terms of the form $(α_S\ln(Q^2/m_c^2))^n$ in this regime. I conclude that some major differences in PDF sets are largely due to the choice of flavour scheme used.

hep-ph↗