from abc import ABC, abstractmethod
import numpy as np
import pineappl
from scipy.interpolate import RectBivariateSpline
from . import constants
[docs]class StructureFunction(ABC):
"""Abstract class for the DIS structure functions"""
[docs] @abstractmethod
def fxq(self, x, q):
r"""
Abstract method returning the value of a DIS structure functions.
Parameters
----------
x : float
Bjorken x
q : float
DIS hard scale
Returns
-------
F_{2,L}: float
Structure function F2 or FL
"""
pass
[docs]class InterpStructureFunction(StructureFunction):
"""
Compute an interpolated structure function convoluting an FKtable
with a PDF.
"""
def __init__(self, path_to_fktable, pdfs):
self.fktable = pineappl.fk_table.FkTable.read(path_to_fktable)
x = np.unique(self.fktable.bin_left(1))
q2 = np.unique(self.fktable.bin_left(0))
self.q2_max = max(q2)
predictions = self.fktable.convolute_with_one(2212, pdfs.xfxQ2)
grid2D = predictions.reshape(len(x), len(q2))
self.interpolator = RectBivariateSpline(x, q2, grid2D)
[docs] def fxq(self, x, q):
r"""
Compute the DIS structure function interpolating the grid.
Parameters
----------
x : float
Bjorken x
q : float
DIS hard scale
Returns
-------
F_{2,L}: float
Structure function F2 or FL
"""
return self.interpolator(x, q**2)[0, 0]
[docs]class F2LO(StructureFunction):
"""Analytically compute the structure function F2 at leading order."""
def __init__(self, pdfs, theory):
self.pdfs = pdfs
self.thresh_c = theory["kcThr"] * theory["mc"]
self.thresh_b = theory["kbThr"] * theory["mb"]
self.thresh_t = theory["ktThr"] * theory["mt"]
if theory["MaxNfPdf"] <= 5:
self.thresh_t = np.inf
if theory["MaxNfPdf"] <= 4:
self.thresh_b = np.inf
if theory["MaxNfPdf"] <= 3:
self.thresh_c = np.inf
if theory["IC"] == 1:
self.thresh_c = 0.0
self.eq2 = [constants.ED2, constants.EU2] * 3 # d u s c b t
[docs] def fxq(self, x, q):
r"""
Analytically compute F2LO.
Parameters
----------
x : float
Bjorken x
q : float
DIS hard scale
Returns
-------
F_2^{LO} : float
Structure function F2 at LO
"""
# at LO we use ZM-VFS
if q < self.thresh_c:
nf = 3
elif q < self.thresh_b:
nf = 4
elif q < self.thresh_t:
nf = 5
else:
nf = 6
res = 0
pdfs_values = self.pdfs.xfxQ(x, q)
for i in range(1, nf + 1):
res += self.eq2[i - 1] * (pdfs_values[i] + pdfs_values[-i])
return res