794 research outputs found
Cosmology in modified -gravity
In present paper we propose further modification of -gravity (where
is trace of energy-momentum tensor) by introducing higher derivatives
matter fields. We discuss stability conditions in proposed theory and find
restrictions for parameters to prevent appearance of main type of
instabilities, such as ghost-like and tachyon-like instabilities. We derive
cosmological equations for a few representations of theory and discuss main
differences with convenient -gravity without higher derivatives. It is
demonstrated that in presented theory inflationary scenarios appears quite
naturally even in the dust-filled Universe without any additional matter
sources. Finally we construct inflationary model in one of the simplest
representation of the theory, calculate main inflationary parameters and find
that it may be in quite agreement with observations
Stability in higher-derivative matter fields theories
We discuss possible instabilities in higher-derivative matter fields
theories. These theories has two free parameters and . By
using dynamical system approach we explicitly demonstrate that for stability of
Minkowski space in expanding Universe it is need condition . By
using quantum field theory approach we also find additional restriction for
parameters which is need to avoid tachyon-like
instability
Competing ideologies of Russia's civil society
Many analysts and public opinion makers in the West conflate the notions of Russia’s non-systemic liberal opposition and the country’s civil society. Indeed, despite garnering the support of a minority of Russia’s population, non-systemic liberal opposition represents a well-organized civic group with a clearly articulated agenda and the ability to take action. Yet, does Russia’s civil society end there? A closer look at the country’s politics shows that Russia has a substantial conservative-traditionalist faction that has also developed agenda for action and formulated opinions. This group is anti-liberal rather than illiberal ideologically and pro-strong state/pro a geopolitically independent Russia rather than pro-Kremlin politically. The interaction between liberal and conservative civic groups represents the battle of meanings, ideas, and ethics, and ultimately determines the future trajectory of Russia’s evolution. Thus, the analysis of Russia’s civil society must represent a rather more nuanced picture than a mere study of the liberal non-systemic opposition. This article will examine the complexity of Russia’s civil society scene with reference to the interplay between the liberal opposition and conservative majority factions. The paper will argue that such complexity stems from ideological value pluralism that falls far beyond the boundaries of the liberal consensus, often skewing our understanding of political practice in Russia
Numerical integration of Heath-Jarrow-Morton model of interest rates
We propose and analyze numerical methods for the Heath-Jarrow-Morton (HJM)
model. To construct the methods, we first discretize the infinite dimensional
HJM equation in maturity time variable using quadrature rules for approximating
the arbitrage-free drift. This results in a finite dimensional system of
stochastic differential equations (SDEs) which we approximate in the weak and
mean-square sense using the general theory of numerical integration of SDEs.
The proposed numerical algorithms are computationally highly efficient due to
the use of high-order quadrature rules which allow us to take relatively large
discretization steps in the maturity time without affecting overall accuracy of
the algorithms. Convergence theorems for the methods are proved. Results of
some numerical experiments with European-type interest rate derivatives are
presented.Comment: 48 page
- …