1,967,040 research outputs found
R. F. and D. C. F. McEwin
No full text"SX11030 R.F. McEwin 2'14 Aust Field Reg Served In Darwin July 1941 - Jan 1943 _____ SX11081 D.C.F. McEwin 2'14 Aust Field Reg Served In Darwin July 1941 - Jan 1943"SX11030 R. F. McEwin 2'14 Australian Field Regiment Served In Darwin July 1941 - January 1943 ____ SX11081 D. C. F. McEwin 2'14 Australian Field Regiment Served In Darwin July 1941 - January 1943
On spectral measures for certain unitary representations of R. Thompson's group F
No full textThe Hilbert space H of backward renormalisation of an anyonic quantum spin chain affords a unitary representation of Thompson’s group F via local scale transformations. The group F is discrete and mysterious in many ways so the obvious questions of irreducibility and distinctness of these representations appear difficult and in a first step towards solving them we calculate the spectral measures of group elements in the representation. Given a vector in the canonical dense subspace of H we calculate the corresponding spectral measure and illustrate with some examples. To do this calculation we introduce the “essential part” (intimately related to the conjugacy class) of an element. The spectral measure for any vector in H is, apart from possibly finitely many eigenvalues, absolutely continuous with respect to
Lebesgue measure. The same considerations and results hold for the Brown-Thompson groups Fn (for which F = F2)
F & R, Ludmilla, Schutzmarke registriert
No full textF & R, LUDMILLA, SCHUTZMARKE REGISTRIERT
F & R, Ludmilla, Schutzmarke registriert ( -
Cosmological consequences of f(R) gravity
No full textreservedIn this thesis, we are focusing on a theory called f(R) gravity, obtained from modifications of General Relativity (GR) by adding higher powers of the Ricci scalar into the standard GR action. By introducing additional terms to the action, we aim to replicate the observed evolution of the Universe without being hindered by the problems of the existence of dark matter and dark energy and address some other interesting phenomena in the universe such as gravitational waves and cosmological perturbations.In this thesis, we are focusing on a theory called f(R) gravity, obtained from modifications of General Relativity (GR) by adding higher powers of the Ricci scalar into the standard GR action. By introducing additional terms to the action, we aim to replicate the observed evolution of the Universe without being hindered by the problems of the existence of dark matter and dark energy and address some other interesting phenomena in the universe such as gravitational waves and cosmological perturbations
F & R, Randl Ia Ia, Schutzmarke registriert
No full textF & R, RANDL IA IA, SCHUTZMARKE REGISTRIERT
F & R, Randl Ia Ia, Schutzmarke registriert ( -
Asymptotically Schwarzschild solutions in f (R) extension of general relativity
No full textWe address the question of how to build a class of f(R) extensions of General Relativity which are compatible with solar system experiments, without making any preliminary assumption on the properties of f. The aim is reached by perturbatively solving the modified Einstein equations around a Schwarzschild background and retrieving a posteriori the corresponding f(R). This turns out to be non analytical in R=0 and should be intended as the leading correction to the Einstein-Hilbert action in the low curvature limit. The parameters characterizing the f(R) class are then set by constraining the corrections to four different local tests with the observations. The result is a class of f(R) theories built up from a purely bottom-up approach and compatible with the local tests. At a more general level, this result can help constraining exact f(R) models working in Cosmology, since it provides the correct local limit. Further developments and possible extensions of the approach to Cosmology are also discussed
Redundant operators in the exact renormalisation group and in the f(R) approximation to asymptotic safety
No full textIn this paper we review the definition and properties of redundant operators in the exact renormalisation group. We explain why it is important to require them to be eigenoperators and why generically they appear only as a consequence of symmetries of the particular choice of renormalisation group equations. This clarifies when Newton’s constant and or the cosmological constant can be considered inessential. We then apply these ideas to the Local Potential Approximation and approximations of a similar spirit such as the f (R) approximation in the asymptotic safety programme in quantum gravity. We show that these approximations can break down if the fixed point does not support a ‘vacuum’ solution in the appropriate domain: all eigenoperators become redundant and the physical space of perturbations collapses to a point. We show that this is the case for the recently discovered lines of fixed points in the f (R) flow equations
R., F. an Herman Grimm (1 Brief)
No full textR., F. AN HERMAN GRIMM (1 BRIEF)
R., F. an Herman Grimm (1 Brief) (Br4220)
Brief 4220 (Br4220
Weak lensing peak count as a probe of f(R) theories
Get PDFWeak gravitational lensing by galaxy clusters on faint higher redshift galaxies has been traditionally used to study the cluster mass distribution and as a tool to identify clusters as peaks in the shear maps. However, it becomes soon clear that peak statistics can also be used as a way to constrain the underlying cosmological model due to its dependence on both the cosmic expansion rate and the growth rate of structures. This feature makes peak statistics particularly interesting from the point of view of discriminating between General Relativity and modified gravity. Here we consider a general class of f(R) theories and compute the observable mass function based on the aperture mass statistics. We complement our theoretical analysis with a Fisher matrix forecast of the constraints that an Euclid-like survey can impose on the f(R) model parameters. We show that peak statistics alone can in principle discriminate between General Relativity and f(R) models and strongly constrain the f(R) parameters that are sensitive to the non-linear growth of structure. However, further analysis is needed in order to include possible selection function in the peaks redshift determination
Disentangling the f - Duality
Get PDFMotivated by UV realisations of Starobinsky-like inflation models, we study generic exponential plateau-like potentials to understand whether an exact -formulation may still be obtained when the asymptotic shift-symmetry of the potential is broken for larger field values. Potentials which break the shift symmetry with rising exponentials at large field values only allow for corresponding -descriptions with a leading order term with , regardless of whether the duality is exact or approximate. The -term survives as part of a series expansion of the function and thus cannot maintain a plateau for all field values. We further find a lean and instructive way to obtain a function describing -inflation which breaks the shift symmetry with a monomial, and corresponds to effectively logarithmic corrections to an model. These examples emphasise that higher order terms in -theory may not be neglected if they are present at all. Additionally, we relate the function corresponding to chaotic inflation to a more general Jordan frame set-up. In addition, we consider -duals of two given UV examples, both from supergravity and string theory. Finally, we outline the CMB phenomenology of these models which show effects of power suppression at low-
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