From a seminar, I heard that energy-momentum relation (E^2=m^2+p^2) is
modified by UV/IR mxing.
In other words, the speaker claimed that the lowest energy is achived
not by zero momentum, but by non-zero momentum. Could somebody refer
me to a relevant paper?
Sorry, I'm not sure I can refer you to immediately relevant papers.
The concept of UV/IR mixing that I've seen came up in the context of
non-commutative field theory. That is, field theory defined on a space-
time where coordinates do not commute. A standard reference for
physicists is a paper by Douglass & Nekrasov . The mathematical
principles of non-commutative spaces are founded in the non-
commutative geometry of Alain Connes . You may find some useful
information in these references.
Hope this helps.
 Douglass & Nekrasov, Noncommutative field theory,
Rev. Mod. Phys. 73, pp.977-1029 (2001)
 Connes, Noncommutative Geometry, Academic Press (1994)