1,721,007 research outputs found
Black holes in ultraviolet-complete Hořava gravity
No full textHoˇrava gravity is a proposal for completing general relativity in the ultraviolet by interactions that violate Lorentz invariance at very high energies. We focus on (2+1)-dimensional projectable Hoˇrava gravity, a theory which is renormalizable and perturbatively ultraviolet-complete, enjoying an asymptotically free ultraviolet fixed point. Adding a small cosmological constant to regulate the long distance behavior of the metric, we search for all circularly symmetric stationary vacuum solutions with vanishing angular momentum and approaching the de Sitter metric with a possible angle deficit at infinity. We find a two-parameter family of such geometries. Apart from the cosmological de Sitter horizon, these solutions generally contain another Killing horizon and should therefore be interpreted as black holes from the viewpoint of the low-energy theory. Contrary to naive expectations, their central singularity is not resolved by the higher derivative terms present in the action. It is unknown at present if these solutions form as a result of gravitational collapse.
The only solution regular everywhere is just the de Sitter metric devoid of any black hole horizo
Precision theoretical methods for large-scale structure of the Universe
Get PDFWe develop new analytic methods to accurately describe the formation of cosmic large-scale structure. These methods are based on the path integral formalism and allows one to efficiently address a number of long-standing problems in the field.
We describe the non-linear evolution of the baryon acoustic oscillations (BAO) in the distribution of matter. We argue for the need for resummation of large infrared (IR) enhanced contributions from bulk flows. We show how this can be done via a systematic resummation of Feynman diagrams guided by well-defined power counting rules. We formulate IR resummation both in real and redshift spaces. For the latter we develop a new method that maps cosmological correlation functions from real to redshift space and retains their IR finiteness. Our results agree well with the N-body simulation data at the BAO scales. This establishes IR resummation within our approach as a robust and complete procedure and provides a consistent theoretical model for the BAO feature in the statistics of matter and biased tracers in real and redshift spaces.
Eventually, we perform a non-perturbative calculation of the 1-point probability distribution function (PDF) for the spherically-averaged matter density field. We evaluate the PDF in the saddle-point approximation and show how it factorizes into an exponent given by a spherically symmetric saddle-point solution and a prefactor produced by fluctuations. The prefactor splits into a monopole contribution which is evaluated exactly, and a factor corresponding to aspherical fluctuations. The latter is crucial for the consistency of the calculation: neglecting it would make the PDF incompatible with translational invariance. We compute the aspherical prefactor using a combination of analytic and numerical techniques, identify the sensitivity to the short-scale physics and argue that it must be properly renormalized. Finally, we compare our result with N-body simulation data and find an excellent agreement.LPP
One-Point Matter PDF’s Beyond TopHat Filters
Get PDFIn this thesis, I studied the one-point probability distribution function (PDF) for averaged matter densities over spherical cells, which can be used to non-perturbatively
probe the large-scale structure of our universe. The PDF depends on a function,
known as the filter/window function, which takes some weighted average over the
observed matter density within each cell. This averaging allows one to study the density field as some smoothed function rather than discrete points. In order to consider filters of different kinds, the PDF’s are constructed numerically using Python code. The PDF is analytically modeled using a path integral framework. By considering
a family of radial window functions interpolating between the TopHat and Gaussian
filters in coordinate space, I investigated the sensitivity of the PDF to the shape
of the window function. It was found that the sensitivity is rather mild suggesting
that the PDF is robust against the precise choice of the filter. Effective field theory
(EFT) corrections were included and used to examine how sensitive different filters
are to short-scale physics. Similar to the PDF, the effects coming from short-scale
physics appeared weakly dependent on the choice of filter, regardless of how smooth
the filter’s boundary was. The contribution coming from aspherical fluctuations to the
collapse dynamics of the cell were computed by comparing the numerical PDF to
high-resolution N-body simulations. It was found that this contribution factorizes as a prefactor to the PDF, which is redshift independent, with the exception of smaller
sized cells which display some mild redshift dependent shifting. These discrepancies
are thought to be associated with two-loop corrections to the PDF. We expect this
model to be flexible enough to study beyond the ΛCDM model and act as a probe
for new fundamental physics.ThesisMaster of Science (MSc)In this thesis, I study the statistics of matter distributions in our universe. Their
statistics are expected to be dependent on how we choose to average over the matter
content in a particular patch in the sky. For this work, I wrote Python code which
calculates the probabilities of these matter densities given an arbitrary averaging
scheme. After examining several cases, it was found that the statistics were qualitatively similar to one another. This suggests an overall universality in the statistics of matter densities in our universe
Open Quantum Dynamics On Lie Group: An Effective Field Theory Approach
Get PDFIn this thesis, we address construction of effective action for the dissipative systems whose
configuration space coincides with a Lie group. We start by generalizing the classical
system plus reservoir model to the case of position dependent Ohmic dissipation. This is
achieved by coupling the system to a field living in one extra dimension. Then, employing
the Schwinger-Keldysh technique, we construct the general influence functional for a
system on a Lie group which includes the classical contribution and the first quantum
correction within the linear response approximation. Abandoning the linear response
assumption, we generalize the results by requiring the invariance under the dynamical
Kubo-Martin-Schwinger symmetry. This gives us the most general influence functional
with nonlinearly realized symmetry. We explore its systematic reduction to the case of
strictly Ohmic dissipation. Finally, we revisit the field theoretic model of the bath and
show that it produces both the leading and first subleading parts of the most general
influence functional at high temperature.ThesisDoctor of Philosophy (PhD
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
From scale invariance to Lorentz symmetry
No full textIt is shown that a unitary translationally invariant field theory in (1+1) dimensions satisfying isotropic scale invariance, standard assumptions about the spectrum of states and operators and the requirement that signals propagate with finite velocity possesses an infinite dimensional symmetry given by one or a product of several copies of conformal algebra. In particular, this implies presence of one or several Lorentz groups acting on the operator algebra of the theory.It is shown that a unitary translationally invariant field theory in 1+1 dimensions, satisfying isotropic scale invariance, standard assumptions about the spectrum of states and operators, and the requirement that signals propagate with finite velocity, possesses an infinite dimensional symmetry given by one or a product of several copies of conformal algebra. In particular, this implies the presence of one or several Lorentz groups acting on the operator algebra of the theory.It is shown that a unitary translationally invariant field theory in (1+1) dimensions satisfying isotropic scale invariance, standard assumptions about the spectrum of states and operators and the requirement that signals propagate with finite velocity possesses an infinite dimensional symmetry given by one or a product of several copies of conformal algebra. In particular, this implies presence of one or several Lorentz groups acting on the operator algebra of the theory
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