Discretely evanescent dark energy

Robot-controlled optical fibers will help create 3D map of the cosmos.

The accelerated expansion of the universe has now been confirmed by several independent observations including those of high redshift type Ia supernovae, and the cosmic microwave background combined with the large scale structure of the universe. Another way of presenting this kinematic property of the universe is to postulate the existence of a new and exotic entity, with negative pressure, the dark energy (DE). In spite of observationally well established, no single theoretical model provides an entirely compelling framework within which cosmic acceleration or DE can be understood. At present all existing observational data are in agreement with the simplest possibility that the cosmological constant be a candidate for DE. This case is internally self-consistent and noncontradictory. The extreme smallness of the cosmological constant expressed in either Planck, or even atomic units means only that its origin is not related to strong, electromagnetic, and weak interactions. Although in this case DE reduces to only a single fundamental constant we still have no derivation from any underlying quantum field theory for its small value. From the principles of quantum cosmologies, for example, it is possible to obtain the reason for an inverse-square law for the cosmological constant with no conflict with observations. Despite the fact that this general expression is well known, in this work we introduce families of analytical solutions for the scale factor different from the current literature. The knowledge of the scale factor behavior might shed some light on these questions mentioned above since the entire evolution of a homogeneous isotropic universe is contained in the scale factor. We use different parameters for these solutions and with these parameters we establish a connection with the equation of state for different DE scenarios.

A formula for calculating dark energy is established through derivation. The result is tested on the basis of the available data from the MAX PLANCK Institute for Radio Astronomy. The universe's dark matter has been computed. There is a balance sheet created and the most important formulas compiled. Summary: The rudiments of a theory of dark energy. The theoretical result is confronted with the numerical value calculated from the available data. Excellent matching of numerical values resulting in three independent paths makes the approach plausible. The approach is credible because of the excellent matching of numerical values that produces three separate routes. The task at hand is comparable to Kepler's planetary orbital rules. Only Isaac Newton gave Kepler's laws a theoretical foundation, which Thomass Gornitz provides here. Niels Bohr, who computed the energy levels of the hydrogen atom and the frequencies of spectral lines, theoretically supported the empirical Balmer formula for the spectral line frequencies in the arc spectrum of the hydrogen atom. A mysterious element known as dark energy is theorized to accelerate the universe's expansion by repelling matter. Theorists have proposed a variety of methods to calculate dark energy over the years. Numerous theories, however, fail to apply a metric structure to gravity or energy momentum conservation even when they satisfy strict local tests. The most popular option for dark energy is the cosmological constant, often known as vacuum energy density. By its very nature, dark energy is a low-energy phenomenon that is dispersed. It is not present in galaxies or galaxies in clusters and it is probably unlikely to be found in laboratory research. The repellent dark energy that hastens the universe's expansion could be explained if the cosmological constant is the vacuum energy of space. Nobody, however, is aware of the cosmological constant's existence or the amount that might be assigned to it in order to calculate the universe's acceleration. Any two matter fields can interact with each other in particle physics or on a more theoretical level, according to a possible process called the interaction of dark matter and dark energy. The phenomenological theory in question has aroused the interest of the cosmology community for a number of reasons. As in the interaction model, where dark energy decays into dark matter, interacting models of DM and DE are an equivalent description of the dark sector of the universe that have undergone extensive research and are motivated by a viable explanation to the so called coincidence and cosmological constant concerns. Keywords Dark energy; Dark matter; Calculation; PLANCK time; Age of the universe; Cosmic information

The 1998 discovery that the universe is accelerating set off an enormous amount of activity, both theoretical and observational. The original result, from two groups observing the Hubble diagram of Type Ia supernovae, has since been verified by a variety of independent types of observations. It seems clear that our universe really is accelerating; what remains a mystery is why.The most straightforward explanation for the universe's acceleration is the presence of a dark energy component comprising 70% of the universe. In order to fit the data, dark energy must have two features: it should be smoothly distributed, so as not to show up in dynamical studies of galaxies and clusters, and its density should be nearly constant as the universe expands, to provide the persistent impulse necessary to make the universe accelerate.The simplest candidate for dark energy is vacuum energy, equivalent to Einstein's cosmological constant. Simple estimates from quantum field theory indicate that vacuum energy should exist – indeed, in an amount larger than what we observe by a factor of 10120. This discrepancy, the 'cosmological constant problem', led to a widespread assumption that some mysterious mechanism worked to set the vacuum energy precisely to zero. If the dark energy really is a cosmological constant, we must find a mechanism to suppress its natural value without driving it all the way to vanishing.Alternatively, the dark energy could be a dynamical field, albeit one that changes very gradually with time. Such a case is observationally distinguishable, at least in principle, from that of a truly constant vacuum energy. Constraints on the evolution of the dark-energy density come from a variety of measurements, and improving the precision of these techniques is a major goal of the next decade in cosmology.Most dramatically, there might not be any dark energy at all, even if the universe is accelerating – a possibility that is well-explored in this focus issue of New Journal of Physics. Two possibilities present themselves. On the one hand, general relativity could break down on cosmological scales, forcing us to a new theory of gravity. In that case, we may use other observed phenomena to put limits on the way in which gravity could deviate from Einstein's theory. On the other hand, general relativity could be correct, but differ in its true predictions from the simple approximations we are used to applying. Such a possibility is both dramatically different from more conventional approaches, and yet radically conservative, attempting to explain all of the accumulated observations with nothing more than matter particles and ordinary general relativity. Only a great deal of additional theoretical investigation and observational progress will be able to distinguish which of these possibilities explains the behaviour of our universe on large scales.The articles below represent the first contributions and further additions will appear.Focus on Dark Energy ContentsCosmic clocks, cosmic variance and cosmic averages David L WiltshireDark energy, a cosmological constant, and type Ia supernovae Lawrence M Krauss, Katherine Jones-Smith and Dragan HutererCosmological dark energy: prospects for a dynamical theory Ignatios Antoniadis, Pawel O Mazur and Emil MottolaPredictive power of strong coupling in theories with large distance modified gravity G Dvali Constraints on dynamical dark energy: an update Alessandro Melchiorri, Barbara Paciello, Paolo Serra and Anze Slosar Scaling solutions to 6D gauged chiral supergravity Andrew Tolley, C P Burgess, Claudia de Rham and D Hoover Modified-source gravity and cosmological structure formation Sean Carroll, I Sawicki, A Silvestri and M Trodden On cosmic acceleration without dark energy E W Kolb, Sabino Matarrese and A Riotto Sean Carroll, California Institute of Technology, Pasadena, USA

The extended chiral quark model confronts QCD

We have considered a cosmological model of holographic dark energy interacting with dark matter and another unknown component of dark energy of the universe. We have assumed two interaction terms Q and Q′ in order to include the scenario in which the mutual interaction between the two principal components (i.e., holographic dark energy and dark matter) of the universe leads to some loss in other forms of cosmic constituents. Our model is valid for any sign of Q and Q′. If Q<Q′, then part of the dark energy density decays into dark matter and the rest in the other unknown energy density component. But if Q>Q′, then dark matter energy receives from dark energy and from the unknown component of dark energy. Observation suggests that dark energy decays into dark matter. Here we have presented a general prescription of a cosmological model of dark energy which imposes mutual interaction between holographic dark energy, dark matter and another fluid. We have obtained the equation of state for the holographic dark energy density which is interacting with dark matter and other unknown component of dark energy. Using first law of thermodynamics, we have obtained the entropies for holographic dark energy, dark matter and other component of dark energy, when holographic dark energy interacting with two fluids (i.e., dark matter and other component of dark energy). Also we have found the entropy at the horizon when the radius (L) of the event horizon measured on the sphere of the horizon. We have investigated the GSL of thermodynamics at the present time for the universe enveloped by this horizon. Finally, it has been obtained validity of GSL which implies some bounds on deceleration parameter q.

In this thesis I study the effects of different Dark Energy models on galaxy formation via numerical simulations. I investigate systems around and be- low Milky-Way masses and describe the effects of dark energy at galactic and sub-galactic scales. Firstly, I analyze high-resolution hydrodynamical simulations of three disc galaxies in dynamical dark energy models. While overall stellar feedback remains the driving mechanisms in shaping galaxies, the effect of the dark energy parametrization plays a larger role than pre- viously thought. Secondly, I broaden the galaxy sample by simulating a 80 Mpc/h side cube of our universe using the same dynamical dark energy mod- els. I show that resolution is a crucial ingredient so that baryonic feedback mechanisms can enhance differences between cosmological models. Thirdly, I investigate the effects of dynamical dark energy on dwarf mass scales. I find that there is more variation from object to object (due to the stochasticity of star formation at these scales) than between the same object in different cosmological models, which makes it hard for observations to disentangle different dark energy scenarios. In the second part of this thesis I investi- gate the effects of coupled dark energy models on galactic and sub-galactic scales via dark matter only high-resolution simulations. I find that coupled models decrease concentrations of (Milky-Way-like) parent haloes and also reduce the number of subhaloes orbiting around them. This improves the agreement with observations and, hence, makes these cosmologies attractive alternatives to a cosmological constant.

In order to make useful comparisons of different dark energy experiments, it is important to choose the appropriate figure of merit (FoM) for dark energy constraints. Here we show that for a set of dark energy parameters ${{f}_{i}}$, it is most intuitive to define $\mathrm{FoM}=1/\sqrt{\mathrm{det}\mathrm{Cov}({f}_{1},{f}_{2},{f}_{3},\dots{})}$, where $\mathrm{Cov}({f}_{1},{f}_{2},{f}_{3},\dots{})$ is the covariance matrix of ${{f}_{i}}$. In order for this FoM to represent the dark energy constraints in an optimal manner, the dark energy parameters ${{f}_{i}}$ should have clear physical meaning and be minimally correlated. We demonstrate two useful choices of ${{f}_{i}}$ using 182 SNe Ia (from the HST/GOODS program, the first year Supernova Legacy Survey, and nearby SN Ia surveys), $[R({z}_{*}),{l}_{a}({z}_{*}),{\ensuremath{\Omega}}_{b}{h}^{2}]$ from the five year Wilkinson Microwave Anisotropy Probe observations, and Sloan Digital Sky Survey measurement of the baryon acoustic oscillation scale, assuming the Hubble Space Telescope prior of ${H}_{0}=72\ifmmode\pm\else\textpm\fi{}8\text{ }\text{ }(\mathrm{km}/\mathrm{s})\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$, and without assuming spatial flatness. We find that for a dark energy equation of state linear in the cosmic scale factor $a$, the correlation of $({w}_{0},{w}_{0.5})$ [${w}_{0}={w}_{X}(z=0)$, ${w}_{0.5}={w}_{X}(z=0.5)$, with ${w}_{X}(a)=3{w}_{0.5}\ensuremath{-}2{w}_{0}+3({w}_{0}\ensuremath{-}{w}_{0.5})a$] is significantly smaller than that of $({w}_{0},{w}_{a})$ [with ${w}_{X}(a)={w}_{0}+(1\ensuremath{-}a){w}_{a}$]. In order to obtain model-independent constraints on dark energy, we parametrize the dark energy density function $X(z)={\ensuremath{\rho}}_{X}(z)/{\ensuremath{\rho}}_{X}(0)$ as a free function with ${X}_{0.5}$, ${X}_{1.0}$, and ${X}_{1.5}$ [values of $X(z)$ at $z=0.5$, 1.0, and 1.5] as free parameters estimated from data. If one assumes a linear dark energy equation of state, current observational data are consistent with a cosmological constant at 68% C.L. If one assumes $X(z)$ to be a free function parametrized by $({X}_{0.5},{X}_{1.0},{X}_{1.5})$, current data deviate from a cosmological constant at $z=1$ at 68% C.L., but are consistent with a cosmological constant at 95% C.L. Future dark energy experiments will allow us to dramatically increase the FoM of constraints on $({w}_{0},{w}_{0.5})$, and of $({X}_{0.5},{X}_{1.0},{X}_{1.5})$. This will significantly shrink the dark energy parameter space to either enable the discovery of dark energy evolution, or the conclusive evidence for a cosmological constant.

The discovery of the accelerated expansion of our Universe brought with it a new theoretical entity called dark energy. Within our standard model of cosmology, \lcdm{}, this dark energy component is described by a cosmological constant with a small energy density that does not evolve with space or time. Attempts to attribute physical meaning to the cosmological constant have been unsuccessful, culminating in a collection of problems known as the ``cosmological constant problem and the ``coincidence problem. These have motivated alternative theories of dark energy that aim at relieving some of the theoretically unsatisfactory characteristics of the cosmological constant. Over recent years, observational cosmology has made great leaps in constraining the parameters of the standard model of cosmology. However, with the increasing quantity and quality of data available, a few tensions between different observational probes have started to appear. These have only grown over time and are now of statistical significance. These tensions could have any of the following origins; they arise from unknown and unaccounted systematic errors in the data, from unknown errors in the theoretical modeling and/or from an incomplete model of cosmology. The latter possibility has added motivation for extending the standard model of cosmology, where alternate forms of dark energy are one of many available avenues. The main aim of this work is to explore forms of dark energy with a greater degree of freedom than the cosmological constant. Specifically, dynamical dark energy (DDE) models which allow dark energy to evolve with time and are parametrised by two additional free parameters: $w_0$ and $w_a$. I investigate the current cosmological parameter constraints from a combination of observation data sets and devise a strategy to select 6 cosmologies of interest. I independently modified and ran a total of 12 simulations, evenly split between collissionless and hydrodynamic simulations. Since dark energy affects the expansion history, geometric probes, such as Type Ia supernovae and baryon acoustic oscillations, can constrain the dark energy parameters in a conceptually straightforward manner. However, changes to the expansion history also affect the growth of structure which could make large-scale structure (LSS) statistics potentially powerful and complementary probes. The first part of this work investigates the effect that these cosmologies have on a variety of LSS statistics using large cosmological hydrodynamical simulations. I find that DDE can affect the clustering of matter and haloes at the $\sim10\%$ level, which should be distinguishable with upcoming large-scale structure surveys. DDE cosmologies can also enhance or suppress the halo mass function (with respect to $\Lambda$CDM) over a wide range of halo masses. The internal properties of haloes are minimally affected by changes in DDE, however. The second part of this work investigates the separability of the cosmology and baryonic physics. I quantify to what extent these two processes affect each other, or in other words, how correlated they are. I show that the impact of baryons and associated feedback processes is largely independent of the change in cosmology and that these processes can be modelled separately to typically better than a few percent accuracy.

Science sets itself apart from other paths to truth by recognizing that even its greate practitioners sometimes err.

In general relativity, the cosmological constant introduces the idea of space containing intrinsic energy. Yet, when dark energy is equated with the vacuum energy density predicted by the Standard Model, the resulting theoretical estimate differs enormously from astronomical observations. Building on superfluid&amp;ndash;vacuum concepts and experimental findings of spontaneously generated, long-sustaining quantum vortices in superfluids, the current study theorises that: (1) Persistent pressure&amp;ndash;energy fluctuations within a superfluid-like spacetime continuum produce localized, Planck-scale energy maxima that collapse into quantum vortices; (2) These vortices are formed continually and gradually transfer the kinetic energy back into the space foam while undergoing deformation; (3) Every vortex behaves as a rotational field composed of curl and divergent components (as per Helmholtz decomposition), with the divergent element creating an radially propagating energy flux that pushes away nearby vortices; (4) The cumulative effect of such microscopic separations is expressed macroscopically as cosmic expansion, akin to the Casimir effect where vacuum fluctuations exert forces on larger bodies; and (5) Consistent with the space foam model, the space continuum remains in a quivering state, producing oscillatory pressure that interacts with the vortex-distancing process. Theoretical formulations are presented that relate the cosmological constant to the sum of divergent energies from local spins. Incorporating the rates of vortex creation and decay yields a time-dependent cosmological constant, attributing the acceleration of cosmic expansion to the changes in these rates within a pulsating energy&amp;ndash;pressure backdrop.

The 2013 cosmology results from the European Space Agency Planck spacecraft provide new limits to the dark energy equation of state parameter. Here we show that Holographic Dark Information Energy (HDIE), a dynamic dark energy model, achieves an optimal fit to the published datasets where Planck data is combined with other astrophysical measurements. HDIE uses Landauer’s principle to account for dark energy by the energy equivalent of information, or entropy, of stellar heated gas and dust. Combining Landauer’s principle with the Holographic principle yields an equation of state parameter determined solely by star formation history, effectively solving the “cosmic coincidence problem”. While HDIE mimics a cosmological constant at low red-shifts, z &lt; 1, the small difference from a cosmological constant expected at higher red-shifts will only be resolved by the next generation of dark energy instrumentation. The HDIE model is shown to provide a viable alternative to the main cosmological constant/vacuum energy and scalar field/ quintessence explanations.

A Universe with finite age also has a finite causal scale. Larger scales cannot affect our local measurements or modelling, but far away locations could have different cosmological parameters. The size of our causal Universe depends on the details of inflation and is usually assumed to be larger than our observable Universe today. To account for causality, we propose a new boundary condition, that can be fulfill by fixing the cosmological constant (a free geometric parameter of gravity). This forces a cancellation of vacuum energy with the cosmological constant. As a consequence, the measured cosmic acceleration cannot be explained by a simple cosmological constant or constant vacuum energy. We need some additional odd properties such as the existence of evolving dark energy (DE) with energy-density fine tuned to be twice that of dark matter today. We show here that we can instead explain the current cosmic acceleration without DE (or modified gravity) as a the result of a primordial inflation with a causal scale smaller than the observable Universe today. Such scale corresponds to half the sky at z = 1 and 60 deg at z= 1100, which is consistent with the anomalous lack of correlations observed in the CMB.

Cosmic acceleration manifested in the early universe as inflation, generating primordial gravitational waves detectable in the cosmic microwave background (CMB) radiation. Cosmic acceleration is occurring again at present as dark energy, detectable in cosmic distance and structure surveys. We explore the intriguing idea of connecting the two occurrences through quintessential inflation by an α-attractor potential without a cosmological constant. For this model we demonstrate robustness of the connection 1 + w 0 ≈ 4/(3N 2 r) between the present day dark energy equation of state parameter w 0 and the primordial tensor to scalar ratio r for a wide range of initial conditions. Analytic and numerical solutions produce current thawing behavior, resulting in a tight relation w a ≈ -1.53(1 + w 0)≈ -0.2 (4 × 10-3/r). Upcoming CMB and galaxy redshift surveys can test this consistency condition. Within this model, lack of detection of a dark energy deviation from Λ predicts a higher r, and lack of detection of r predicts greater dark energy dynamics.

Consistency relations between growth of structure and expansion history observables exist for any physical explanation of cosmic acceleration, be it a cosmological constant, scalar field quintessence, or a general component of dark energy that is smooth relative to dark matter on small scales. The high-quality supernova sample anticipated from an experiment like SNAP and CMB data expected from Planck thus make strong predictions for growth and expansion observables that additional observations can test and potentially falsify. We perform an MCMC likelihood exploration of the strength of these consistency relations based on a complete parametrization of dark energy behavior by principal components. For LCDM, future SN and CMB data make percent level predictions for growth and expansion observables. For quintessence, many of the predictions are still at a level of a few percent with most of the additional freedom coming from curvature and early dark energy. While such freedom is limited for quintessence where phantom equations of state are forbidden, it is larger in the smooth dark energy class. Nevertheless, even in this general class predictions relating growth measurements at different redshifts remain robust, although predictions for the instantaneous growth rate do not. Finally, if observations falsify the whole smooth dark energy class, new paradigms for cosmic acceleration such as modified gravity or interacting dark matter and dark energy would be required.