125373617
One rigorous negative result in quantum field theory
119159767
Haag’s theorem in noncommutative quantum field theory
Haag’s theorem was extended to the general case of noncommutative quantum field theory when time does not commute with spatial variables. It was proven that if S matrix is equal to unity in one of two theories related by unitary transformation, then the corresponding one in the other theory is equal to unity as well. In fact, this result is valid in any SO(1, 1)-invariant quantum field theory, an important example of which is noncommutative quantum field theory.
120070545
Integral equalities for functions that satisfy dispersion relations
120285099
Irreducibility of the set of field operators in NC QFT
Irreducibility of the set of quantum field operators has been proved in noncommutative quantum field theory in the general case when time does not commute with spatial variables.
121953927
Analogue of the Weyl representation of algebra of canonical commutation relations in the case of nonphysical particles
An analogue of the Weyl representation of the algebra of canonical commutation relations is proved to exist in the anti-Fock case achieved in Krein space.
122273916
Pomeranchuk's theorem at asymptotic and finite energies
8090542
Bouncing and accelerating solutions in nonlocal stringy models
A general class of cosmological models driven by a nonlocal scalar field inspired by string field theories is studied. In particular cases the scalar field is a string dilaton or a string tachyon. A distinguished feature of these models is a crossing of the phantom divide. We reveal the nature of this phenomena showing that it is caused by an equivalence of the initial nonlocal model to a model with an infinite number of local fields some of which are ghosts. Deformations of the model that admit exact solutions are constructed. These deformations contain locking potentials that stabilize solutions. Bouncing and accelerating solutions are presented.
119221562
De Sitter Universe in Non-local Gravity
A nonlocal gravity model, which does not assume the existence of a new dimensional parameter in the action and includes a function $f(\Box^{-1} R)$, with $\Box$ the d'Alembertian operator, is considered. The model is proven to have de Sitter solutions only if the function f satisfies a certain second-order linear differential equation. The de Sitter solutions corresponding to the simplest case, an exponential function f, are explored, without any restrictions on the parameters. If the value of the Hubble parameter is positive, the de Sitter solution is stable at late times, both for negative and for positive values of the cosmological constant. Also, the stability of the solutions with zero cosmological constant is discussed and sufficient conditions for it are established in this case. New de Sitter solutions are obtained which correspond to the model with dark matter and stability is proven in this situation for nonzero values of the cosmological constant.
119152817
On bouncing solutions in non-local gravity
A non-local modified gravity model with an analytical function of the d’Alembert operator, is considered. This model has been recently proposed as a possible way of resolving the singularities problem in cosmology. We present exact bouncing solution, which is simpler compared to the already known one in this model, in the sense it does not require an additional matter to satisfy all gravitational equations.
1590579
Dynamics in nonlocal linear models in the Friedmann–Robertson–Walker metric
A general class of cosmological models driven by a nonlocal scalar field inspired by string field theory is studied. Using the fact that the considering linear nonlocal model is equivalent to an infinite number of local models we have found an exact special solution of the nonlocal Friedmann equations. This solution describes a monotonically increasing universe with the phantom dark energy.
115160895
Exact Solutions in Nonlocal Linear Models
A general class of cosmological models driven by a nonlocal scalar field inspired by the string field theory is studied. Using the fact that the considering linear nonlocal model is equivalent to an infinite number of local models we have found an exact special solution of the nonlocal Friedmann equations. This solution describes a monotonically increasing Universe with the phantom dark energy.