A new numerical method for inverse Laplace transforms used to obtain gluon distributions from the proton structure function |
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Authors: | Martin M Block Loyal Durand |
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Institution: | 1.Department of Physics and Astronomy,Northwestern University,Evanston,USA;2.Department of Physics,University of Wisconsin,Madison,USA;3.Aspen,USA |
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Abstract: | We recently derived a very accurate and fast new algorithm for numerically inverting the Laplace transforms needed to obtain
gluon distributions from the proton structure function F2gp(x,Q2)F_{2}^{\gamma p}(x,Q^{2}). We numerically inverted the function g(s), s being the variable in Laplace space, to G(v), where v is the variable in ordinary space. We have since discovered that the algorithm does not work if g(s)→0 less rapidly than 1/s as s→∞, e.g., as 1/s
β
for 0<β<1. In this note, we derive a new numerical algorithm for such cases, which holds for all positive and non-integer negative
values of β. The new algorithm is exact if the original function G(v) is given by the product of a power v
β−1 and a polynomial in v. We test the algorithm numerically for very small positive β, β=10−6 obtaining numerical results that imitate the Dirac delta function δ(v). We also devolve the published MSTW2008LO gluon distribution at virtuality Q
2=5 GeV2 down to the lower virtuality Q
2=1.69 GeV2. For devolution, β is negative, giving rise to inverse Laplace transforms that are distributions and not proper functions. This requires us
to introduce the concept of Hadamard Finite Part integrals, which we discuss in detail. |
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