Holstein B R 1998 Am. J. Phys66 583:
this article discusses a number of techniques employed in the path
integral method, and contains some useful references to the particle
propagator
in a linear potential
Ansoldi S, Aurilia A and Spallucci E 1996
Phys. Rev.D53 870
Aurilia A, Spallucci E and Vanzetta I 1994
Phys. Rev.D506490
Aurilia A, Smailagic A and Spallucci E 1993
Phys. Rev.D47 2536
Dirac P A M 1958
The Principles of Quantum Mechanics,
(London: Oxford University Press)
Feynman R P, reference [6].
This paper, as well as Dirac's original work can be found reprinted
in : Selected Papers on Quantum Electrdynamics
(New York: Schwinger J ed., Dover, 1958)
The path integral approach is discussed
in many textbooks besides that by Feynman and Hibbs, reference
[10].
See, for instance
Felsager B 1981 Geometry, Particles and Fields
(Odense: Odense University Press)
Ramond P 1981 Field Theory, A Modern Primer
(Reading, Massachusetts: Benjamin/Cummings Publishers)
Ryder L H 1985 Quantum Field Theory
(Cambridge: Cambridge University Press)
Schulman L S 1981 Techniques and Applications
of Path Integration
(New York: Wiley)
Swanson M 1992 Path Integrals and Quantum Processes
(New York: Academic Press)