scholarly journals THE UNIVERSE DYNAMICS IN THE TACHYON COSMOLOGY WITH NON-MINIMAL COUPLING TO MATTER

2011 ◽  
Vol 26 (15) ◽  
pp. 1125-1135 ◽  
Author(s):  
H. FARAJOLLAHI ◽  
A. RAVANPAK ◽  
G. F. FADAKAR
Keyword(s):  
Distance Modulus ◽  
Tachyon Field ◽  
Cosmological Redshift ◽  
Redshift Drift ◽  
Phantom Crossing ◽  
Acceleration Of The Universe ◽  
Model Independent ◽  
The Difference ◽  
The Universe

Recently, the tachyon cosmology has been represented as dark energy model to support the current acceleration of the universe without phantom crossing. In this paper, we study the dynamics of the tachyon cosmology in which the field plays the role of tachyon field and also non-minimally coupled to the matter Lagrangian. The model shows current universe acceleration and also phantom crossing in the future. Two cosmological tests are also performed to validate the model; the difference in the distance modulus and the model independent Cosmological Redshift Drift (CRD) test.

scholarly journals COSMIC DYNAMICS IN CHAMELEON COSMOLOGY

2010 ◽  
Vol 19 (05) ◽  
pp. 621-633 ◽  
Author(s):  
H. FARAJOLLAHI ◽  
A. SALEHI
Keyword(s):  
Equation Of State ◽  
Eos Parameter ◽  
Cosmological Redshift ◽  
Cosmological Constraints ◽  
The Past ◽  
Redshift Drift ◽  
History Of ◽  
Model Independent ◽  
The Universe ◽  
Friedmann Robertson Walker

We study in this paper chameleon cosmology applied to Friedmann–Robertson–Walker space, which gives rise to the equation of state (EoS) parameter larger than -1 in the past and less than -1 today, satisfying current observations. We also study cosmological constraints on the model using the time evolution of the cosmological redshift of distant sources, which directly probes the expansion history of the universe. Due to the evolution of the universe's expansion rate, the model-independent cosmological redshift drift (CRD) test is expected to experience a small, systematic drift as a function of time. The model is supported by the observational data obtained from the test.

Cosmic acceleration with tachyon field

2018 ◽  
Vol 33 (34) ◽  
pp. 1850199 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
De Sitter ◽  
Tachyon Field ◽  
Minimal Coupling ◽  
Acceleration Of The Universe ◽  
The Universe

In this study, we examine two models of the scalar field, that is, a normal scalar field and a tachyon scalar field in [Formula: see text] gravity to describe cosmic acceleration of the universe, where [Formula: see text], [Formula: see text] and [Formula: see text] are Ricci curvature scalar, trace of energy–momentum tensor and kinetic energy of scalar field [Formula: see text], respectively. Using the minimal-coupling Lagrangian [Formula: see text], for both the scalar models we obtain a viable cosmological system, where [Formula: see text] and [Formula: see text] are real constants. While a normal scalar field gives a system describing expansion from the deceleration to the late-time acceleration, tachyon field together with [Formula: see text] in the system produces a quintessential expansion which is very close to de Sitter point, where we find a new condition [Formula: see text] for inflation.

scholarly journals First Contemporary Muslim Philosophers Conference

1998 ◽  
Vol 15 (3) ◽  
pp. 167-172
Author(s):  
Ahmad Iftheqar Hussain
Keyword(s):  
Muslim World ◽  
Annual Conference ◽  
Islamic Philosophy ◽  
Saturday Morning ◽  
Philosophical Discourse ◽  
Conference Room ◽  
Cardinal Directions ◽  
The Difference ◽  
The Universe

Early Saturday morning on 16 May 1998, fifty people made their wayinto the conference room of Georgetown University’s SalaamIntercultural Center for the first annual conference of the Association ofContemporary Muslim Philosophers. Looking into their eyes, one couldsee a glimmer of hope and the fire of enthusiasm. Clearly, this was notgoing to be a run of the mill encounter of Muslim minds. Some of thegreatest intellects of the Muslim world were present, among themProfessor Seyyed Hossein Nasr, Dr. T a B JBbir a1 ‘AlwBni, and Dr. KamalHassan. Young students with fresh countenances and effervescent commentswaited to deliberate upon such issues as the difference betweenpublic and private philosophy, the role of postmodernism in the Muslimworld, and why and in what condition does the Muslim intellectual traditionfind itself.Ironically, this occurred in view of an immense Jesuit Crucifix heraldedby the Greek letters alpha and omega, which symbolize Christ.While for some this signified the contradiction and turmoil presentwithin current Muslim philosophical discourse, for others it embodieda promising message. For those who saw it as a positive symbol,including myself, the cross served to illustrate the universe, markingthe four cardinal directions of space, and the surrounding alpha andomega symbolized the all-encompassing nature of the Qur’an. On aterrestrial level, it verified the resilient nature of the Muslim intellectfor, quite obviously, we were a group of Mhims meeting in a Jesuitinstitution to talk about reviving Islamic philosophy. Nevertheless, theuniversal significance of that symbol was realized by the spirit of thegathering and in the profound discussions afforded by all those present.The conference started with a moment of reflection upon the versesof the Qur’an found in Siirat a1 ‘Alaq: ...

scholarly journals How Does a Thought Scream? The Possibility of the New as a Condition of Political Ontology in Gilles Deleuze’s The Time-Image

2020 ◽  
Vol 31 (5) ◽  
pp. 103-130
Keyword(s):  
Critical Distance ◽  
Status Quo ◽  
The Political ◽  
Political Ontology ◽  
Cinema Studies ◽  
The Status ◽  
The Difference ◽  
Time Image ◽  
The Universe

The paper deals with Gilles Deleuze’s The Time-Image not as an essay on the philosophy of cinema but as a theory of political ontology. The meaning of the concept of “scream” must first be clarified. This concept appears in Deleuze’s lectures from 1980 in the context of the sequence of cinema, thought and shock from the second volume of his book Cinema. To indicate the immanent political significance of Deleuze’s cinema studies, the article clarifies the conceptual difference between two types of cinema. The distinction between “the movement-image” and “the time-image” is examined as ontological rather than aesthetic. In particular, the paper shows the conservative effects of “classic” cinema in the context of Henri Bergson’s ontology. The critical potential of modern cinema, which Deleuze considers in The Time-Image, is a condition for undermining the logic of “habit,” which is reproduced by the cinema of “the movement-image.” The condition for a break with this logic is the effect of shock, which is produced by the distinctive characteristics of modern cinema. Deleuze finds the political significance of modern cinema in the context of the possibility of the New which is not predetermined by previous conditions. The rupture with the status quo is ensured by contrasting two concepts of the Whole viewed either as the Open or as the Outside. The difference between them is examined in connection with the critical distance from the ontology of Henri Bergson, which is an imaginary solution of the problem of the New and therefore the problem of conservatism in the universe of “classic” cinema. In order to identify the political significance of “the image-time,” it is necessary to indicate the constitutive role of temporal rupture in modern cinema. It is this logic that provides the effect of shock for thought and allows it to break away from permanent repetition.

scholarly journals Forecasts of redshift drift constraints on cosmological parameters

2019 ◽  
Vol 488 (3) ◽  
pp. 3607-3624 ◽  
Author(s):  
C S Alves ◽  
A C O Leite ◽  
C J A P Martins ◽  
J G B Matos ◽  
T A Silva
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Intensity Mapping ◽  
Cosmological Observations ◽  
Universe Expand ◽  
Redshift Drift ◽  
Expansion Of The Universe ◽  
Model Independent ◽  
Weak Constraints ◽  
The Universe

ABSTRACT Cosmological observations usually map our present-day past light cone. However, it is also possible to compare different past light cones. This is the concept behind the redshift drift, a model-independent probe of fundamental cosmology. In simple physical terms, this effectively allows us to watch the Universe expand in real time. While current facilities only allow sensitivities several orders of magnitude worse than the expected signal, it should be possible to detect it with forthcoming ones. Here, we discuss the potential impact of measurements by three such facilities: the Extremely Large Telescope (the subject of most existing redshift drift forecasts), but also the Square Kilometre Array and intensity mapping experiments. For each of these we assume the measurement sensitivities estimated respectively in Liske et al. (2008), Klockner et al. (2015), and Yu, Zhang & Pen (2014). We focus on the role of these measurements in constraining dark energy scenarios, highlighting the fact that although on their own they yield comparatively weak constraints, they do probe regions of parameter space that are typically different from those probed by other experiments, as well as being redshift dependent. Specifically, we quantify how combinations of several redshift drift measurements at different redshifts, or combinations of redshift drift measurements with those from other canonical cosmological probes, can constrain some representative dark energy models. Our conclusion is that a model-independent mapping of the expansion of the universe from redshift z = 0 to z = 4 – a challenging but feasible goal for the next generation of astrophysical facilities – can have a significant impact on fundamental cosmology.

scholarly journals Torsion in String-Inspired Cosmologies and the Universe Dark Sector

Universe ◽  
2021 ◽  
Vol 7 (12) ◽  
pp. 480
Author(s):  
Nick E. Mavromatos
Keyword(s):  
String Model ◽  
Dark Sector ◽  
Vacuum Model ◽  
Anomaly Cancellation ◽  
Fundamental String ◽  
Primordial Gravitational Waves ◽  
Cosmological Data ◽  
Model Independent ◽  
The Universe

Several aspects of torsion in string-inspired cosmologies are reviewed. In particular, its connection with fundamental, string-model independent, axion fields associated with the massless gravitational multiplet of the string are discussed. It is argued in favour of the role of primordial gravitational anomalies coupled to such axions in inducing inflation of a type encountered in the “Running-Vacuum-Model (RVM)” cosmological framework, without fundamental inflaton fields. The gravitational-anomaly terms owe their existence to the Green–Schwarz mechanism for the (extra-dimensional) anomaly cancellation, and may be non-trivial in such theories in the presence of (primordial) gravitational waves at early stages of the four-dimensional string universe (after compactification). The paper also discusses how the torsion-induced stringy axions can acquire a mass in the post inflationary era, due to non-perturbative effects, thus having the potential to play the role of (a component of) dark matter in such models. Finally, the current-era phenomenology of this model is briefly described with emphasis placed on the possibility of alleviating tensions observed in the current-era cosmological data. A brief phenomenological comparison with other cosmological models in contorted geometries is also made.

scholarly journals Degeneracy pressure of relic neutrinos and cosmic coincidence problem

2013 ◽  
Vol 91 (1) ◽  
pp. 23-26
Author(s):  
Tae Hoon Lee
Keyword(s):  
Theory Model ◽  
Global Symmetry ◽  
Coincidence Problem ◽  
True Vacuum ◽  
Effective Cosmological Constant ◽  
Degeneracy Pressure ◽  
Acceleration Of The Universe ◽  
Constant Energy Density ◽  
The Universe

We consider the universe as a huge νR-sphere formed with degenerate relic neutrinos and suggest that its constant energy density play a role of an effective cosmological constant. We construct the sphere as a bubble of true vacuum in a field theory model with a spontaneously broken U(1) global symmetry, and we interpret the sphere-forming time as the transition time for recent acceleration of the universe. The coincidence problem may be regarded as naturally resolved in this model, because the relic neutrinos can make the νR-sphere at the recent past time during the matter-dominated era.

scholarly journals Artikel 2 van die Nederlandse Geloofsbelydenis as geloofsvooronderstelling in die gesprek tussen wetenskap en geloof

2014 ◽  
Vol 48 (1) ◽  
Author(s):  
Jan A. Erasmus
Keyword(s):  
Word Of God ◽  
The Bible ◽  
The Creation ◽  
The Difference ◽  
Scientific Results ◽  
Science And Faith ◽  
The Universe ◽  
Made In ◽  
The Way

Artikel 2 van die Nederlandse Geloofsbelydenis bely dat God deur twee middele geken word, te wete deur middel van die skepping, onderhouding en regering van die wêreld (waaronder die wetenskap) en deur die heilige en goddelike Woord (die Bybel). Hierdie belydenis is van groot belang vir die gesprek tussen Wetenskap en Teologie. In hierdie artikel word gepoog om die verskille, maar ook die ooreenkomste tussen hierdie twee middele van openbaring uit te lig, elkeen tot sy reg te laat kom, maar hulle ook in balans met mekaar te stel. Die wyse waarop te werk gegaan word, is die volgende: eers word gestel wat vooronderstellings is, asook die plek wat vooronderstellings in die beoefening van wetenskap sowel as geloof inneem. Daarna word nagevors watter perspektiewe artikel 2 van die Nederlandse Geloofsbelydenis as geloofsvooronderstelling vir die wetenskaps- en teologiebeoefening respektiewelik bied. Hieruit word ’n aantal gevolgtrekkings gemaak wat kan help om die problematiek in die wetenskap-geloofsgesprek op te los. Die kernbevinding van hierdie artikel is die volgende: Vanweë die verskil in die aard en die doel tussen Bybelfeite en wetenskaplike navorsingsresultate kan en sal klaarblyklike harmonieprobleme tussen die Skrif en die wetenskap ontstaan. Hierdie is egter slegs klaarblyklike probleme, omdat ’n verrekening van die verskil in die aard en die bedoeling van die wetenskapresultate en die Bybelfeite hierdie probleem sal oplos.Article 2 of the Belgic Confession as faith presupposition in the science-faith debate. Article 2 of the Belgic Confession confesses that God can be known by two means: firstly by studying the creation, preservation and government of the universe (i.e. science) and secondly by studying the Word of God (the Bible). This confession is very important for the discussion between science and faith. In this article the similarities, but also the differences between these two means of revelation are researched. The aim is to set them in balance and in order to let each one come to its own right. The way the research is done is as follows: In the first place the role of presuppositions in both science and faith are determined. Secondly research is done on the perspectives obtained for both science and faith when Article 2 of the Belgic Confession is taken as a faith presupposition. Finally conclusions are made in helping to resolve the differences in the science-faith debate. The main finding is that harmony problems between facts from the Bible and scientific results will occur because of the difference in nature and meaning between these two entities. However, when the set difference in nature and meaning are taken into account, these problems can be resolved.

The role of differential phase contrast in electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 176-177
Author(s):  
E.M. Waddell ◽  
J.N. Chapman ◽  
R.P. Ferrier
Keyword(s):  
Phase Contrast ◽  
Practical Method ◽  
Position Vector ◽  
Differential Phase ◽  
Pure Phase ◽  
Differential Phase Contrast ◽  
The Difference ◽  
Image Position ◽  
First Moment

Dekkers and de Lang (1977) have discussed a practical method of realising differential phase contrast in a STEM. The method involves taking the difference signal from two semi-circular detectors placed symmetrically about the optic axis and subtending the same angle (2α) at the specimen as that of the cone of illumination. Such a system, or an obvious generalisation of it, namely a quadrant detector, has the characteristic of responding to the gradient of the phase of the specimen transmittance. In this paper we shall compare the performance of this type of system with that of a first moment detector (Waddell et al.1977).For a first moment detector the response function R(k) is of the form R(k) = ck where c is a constant, k is a position vector in the detector plane and the vector nature of R(k)indicates that two signals are produced. This type of system would produce an image signal given bywhere the specimen transmittance is given by a (r) exp (iϕ (r), r is a position vector in object space, ro the position of the probe, ⊛ represents a convolution integral and it has been assumed that we have a coherent probe, with a complex disturbance of the form b(r-ro) exp (iζ (r-ro)). Thus the image signal for a pure phase object imaged in a STEM using a first moment detector is b2 ⊛ ▽ø. Note that this puts no restrictions on the magnitude of the variation of the phase function, but does assume an infinite detector.

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