Cosmological Constant Problem Research Articles

Vacuum energy and the cosmological constant problem inκ-Poincaré invariant field theories

We investigate the vacuum energy in $\kappa$-Poincar\'e invariant field theories. It is shown that for the equivariant Dirac operator one obtains an improvement in UV behavior of the vacuum energy and therefore the cosmological constant problem has to be revised.

Electroweak relaxation of cosmological hierarchy

A simple model for the late-time cosmic acceleration problem is presented in the Starobinsky inflation with a negative bare cosmological constant as well as a nonminimal coupling to the Higgs boson. After electroweak symmetry breaking, the Starobinsky inflaton has been frozen until very recently, becoming a thawing quintessence, and a comparable magnitude to the observed dark energy density can be achieved without fine-tuning. Our proposal essentially reduces the cosmological constant problem into the electroweak hierarchy problem, and its late-time behaviour is also consistent with the recently proposed swampland criteria.

Scale symmetry and Weinberg's no-go theorem in the cosmological constant problem

We complete the proof of Weinberg's no-go theorem on the cosmological constant problem in classical gravity when the theory has a (global) scale symmetry. Stimulated with this proof, we explore a solution to the cosmological constant problem by the help of renormalization group equations. We find that the manifestly scale invariant regularization method provides a physically plausible solution to the cosmological constant problem, in particular, to the issue of radiative instability of the cosmological constant.

Self-Reference and Entanglement Network

One of the important concepts in logical studies is the self-reference, which often leads to semantic inconsistencies. In order to resolve this problem, the cyclical time process of self-reference is discussed in terms of computing machines. This approach provides an interconnection between matter and mind that may help to solve one of the important physics predicaments, namely, the cosmological constant problem. On the other hand, entanglement is often considered a natural phenomenon that is clearly distinguishable from classical theory. Moreover, entanglement has been shown to be an essential part of recent developments in quantum computing and quantum cryptography. In this paper, the entanglement swapping protocol is applied to four 2-level non-maximal states, and a new non-trivial class of non-maximal states that approximate the weakest link is examined numerically.

Why Zeldovich Failed to Estimate the Precise Value of Cosmological Constant in Planck Unit?

To meet the cosmological constant problem, we studied the Zeldovich’s proposed solution and evaluated here why he estimated the theoretical value of this constant larger by over 120 orders of magnitude in Planck mass; by theoretically deriving his empirically proposed equation thoroughly. We reported that the mathematical expression of Planck unit is numerically imbalanced thus its numerically incorrect expression, therefore, in this unit he predicted its extreme value and cosmological constant problem persisted there. A modification in this unit has been suggested, subsequently it modified the Zeldovich’s proposed expression and this modified expression estimated the precise value of this cosmological constant later. These findings imply that if the mathematical expression of Planck unit was correct he would have estimated the precise value of this constant alone.

Quantum Field theory in Fractal Space-Time with Negative Hausdorff-Colombeau Dimensions. The Solution Cosmological Constant Problem.

The cosmological constant problem arises because the magnitude of vacuum energy density predicted by quantum field theory is about 120 orders of magnitude larger than the value implied by cosmological observations of accelerating cosmic expansion. We pointed out that the fractal nature of the quantum space-time with negative Hausdorff- Colombeau dimensions can resolve this tension. The canonical Quantum Field Theory is widely believed to break down at some fundamental high-energy cutoff Ʌ* and therefore the quantum fluctuations in the vacuum can be treated classically seriously only up to this high-energy cutoff. In this paper we argue that Quantum Field Theory in fractal space-time with negative Hausdorff-Colombeau dimensions gives high-energy cutoff on natural way. In order to obtain disered physical result we apply the canonical Pauli-Villars regularization up to Ʌ. It means that there exist the ghost-driven acceleration of the univers hidden in cosmological constant.

Resolving the Vacuum Catastrophe: A Generalized Holographic Approach

We address the ~122 orders of magnitude discrepancy between the vacuum energy density at the cosmological scale and the vacuum density predicted by quantum field theory. This disagreement is known as the cosmological constant problem or the “vacuum catastrophe”. Utilizing a generalized holographic model, we consider the total mass-energy density in the geometry of a spherical shell universe (as a first order approximation) and find an exact solution for the currently observed critical density of the universe. We discuss the validity of such an approach and consider its implications to cosmogenesis and universal evolution.

A Final Cure to the Tribulations of the Vacuum in Quantum Theory

Quantum Field Theory seems to be of late anything but unraveling, apparently shifting from crisis to crisis. Undeniably, there seems to be running, for many different reasons, a rampant discomfort with the Standard Model, an extension of QFT aiming at complementing it. Prior to the latest supersymmetry upset, what has been known as the “vacuum castastrophe” or the “cosmological constant problem” resoundingly shook the very foundations of the Theory. Effectively the enormous numeric disparity between its predicted value of the vacuum energy density, an element of utmost significance in the Theory, and the measured value of this quantity from a Relativistic approach has prompted some to qualify this mishap as the biggest predictive failure of any Theory. Like a wounded beast, Quantum Field Theory seems to be left searching for its soul now for almost two decades. Under the umbrella of Quanto-Geometric Theory, we offer here a different approach to the question of the vacuum energy density that demonstrably calculates a sensible and consistent value of this quantity from first axiomatic principles, casting a figure that is in very close match with the cosmological quantity. Therefore in so doing, Quanto-Geometric Theory effectively and definitively cures the long-standing grueling vacuum problem by bridging the gap between the quantum vacuum and the relativistic vacuum.

Quantum Mechanical Explanation for Dark Energy, Cosmic Coincidence, Flatness, Age, and Size of the Universe

AbstractOne of the most important problems in astronomy is the cosmological constant problem in which conventional calculation of vacuum energy density using quantum mechanics leads to a value which is ~10123times more than the vacuum energy estimated from astronomical observations of expanding universe. The cosmic coincidence problem questions why matter energy density is of the same order of magnitude as the vacuum energy density at present time. Finally, the mechanism responsible for spatial flatness is not clearly understood. In this paper, by taking the vacuum as a finite and closed quantum oscillator, we solve all of the above-mentioned problems. At first, by using the purely quantum mechanical approach, we predict that the dark energy density isc4/(GR2) = 5.27×10−10J/m3(whereRis radius of 3-sphere of the universe) and matter energy density isc4/(2GR2) = 2.6×10−10J/m3which match well with astronomical observations. We also prove that dark energy has always been ~66.7% and matter energy has been ~33.3% of the total energy and thus solve the cosmic coincidence problem. Next, we show how flatness of space could be maintained since the early stage of the universe. Finally, using our model, we derive the expression for age and radius of the universe which match well with the astronomical data.

Is Quintessence an Indication of a Time-Varying Gravitational Constant?

A model is presented where the quintessence parameter, w, is related to a time-varying gravitational constant. Assuming a present value of w equals -.98, we predict a current variation of G dot/G = -.06 H0. H0 is Hubbles parameter, G is Newtons constant and G dot is the derivative of G with respect to time. Thus, G has a cosmic origin, is decreasing with respect to cosmological time, and is proportional to H0, as originally proposed by the Dirac-Jordan hypothesis. Within our model, we can explain the cosmological constant fine-tuning problem, the discrepancy between the present very weak value of the cosmological constant, and the much greater vacuum energy found in earlier epochs. To formalize and solidify our model, we give two distinct functions of G(a), the cosmic scale parameter. We treat inverse G as an order parameter, which vanishes at high energies; at low temperatures, it reaches a saturation value, a value we are close to today. Our first function for inverse G is motivated by a charging capacitor; the second treats inverse G by analogy to a magnetic response. Both functions, even though very distinct, give a remarkably similar tracking behavior for w(a). Interestingly, both functions indicate the onset of G formation at a temperature of approximately 7 *1021 degrees Kelvin, in contrast to the concordance model. At the temperature of formation, we find that G has increased to roughly 4*1020 times its present value. For most of cosmic evolution, however, our variable G model gives results similar to the predictions of the concordance model, except in the very early universe, as we shall demonstrate. Within our framework, the weakening of G to its current value G0 is speculated as the true cause for the observed unanticipated acceleration of the universe.

The Solution Cosmological Constant Problem

We introduce Hausdorff-Colombeau measure in respect with negative fractal dimensions. Axiomatic quantum field theory in spacetime with negative fractal dimensions is proposed.Spacetime is modelled as a multifractal subset of $R^{4}$ with positive and negative fractal dimensions.The cosmological constant problem arises because the magnitude of vacuum energy density predicted by quantum field theory is about 120 orders of magnitude larger than the value implied by cosmological observations of accelerating cosmic expansion. We pointed out that the fractal nature of the quantum space-time with negative Hausdorff-Colombeau dimensions can resolve this tension. The canonical Quantum Field Theory is widely believed to break down at some fundamental high-energy cutoff $E$ and therefore the quantum fluctuations in the vacuum can be treated classically seriously only up to this high-energy cutoff. In this paper we argue that Quantum Field Theory in fractal space-time with negative Hausdorff-Colombeau dimensions gives high-energy cutoff on natural way. In order to obtain disered physical result we apply the canonical Pauli-Villars regularization up to $E$. It means that there exist the ghost-driven acceleration of the univers hidden in cosmological constant.

Energy and Metric Gauging in the Covariant Theory of Gravitation

Relations for the relativistic energy and metric are analyzed inside and outside the body in the framework of the covariant theory of gravitation. The methods of optimal energy gauging and equations for the metric are chosen. It is shown that for the matter inside the body a procedure is required to average the physical quantities, including the cosmological constant and the scalar curvature. For the case of the relativistic uniform system, the cosmological constant and the scalar curvature are explicitly calculated, which turn out to be constant values inside the body and are assumed to be equal to zero outside the body. Comparison of the cosmological constants inside a proton, a neutron star and in the observable Universe allows us to explain the cosmological constant problem arising in the Lambda-CDM model

Graceful exit for the cosmological constant damping scenario

We present a broad and simple class of scalar-tensor scenarios that successfully realize dynamical damping of the effective cosmological constant, therefore providing a viable dynamical solution to the fine-tuning or "old" cosmological constant problem. In contrast to early versions of this approach, pioneered in the works of A. Dolgov in the 1980es, these do not suffer from unacceptable variations of Newton's constant, as one aims at a small but strictly positive (rather than zero) late-time curvature. In our approach, the original fine-tuning issue is traded for a hierarchy of couplings, and we further suggest a way to naturally generate this hierarchy based on fermion condensation and softly broken field shift symmetry.

New wormhole solution in de Sitter space

We present a new wormhole solution connecting two points of the same universe separated by finite distance. Virtually all the existing solutions connect two disconnected universes, or two points of the same universe that are infinitely far away. We construct our solution by placing two black holes at the antipodes of the closed de Sitter space with a matter shell between them. The gravitational action of the matter shell and cosmological constant counteracts attractive gravity between the black holes and makes the whole configuration static. The whole space outside the wormhole mouths is causally connected, even though the wormhole is not traversable. The stress energy tensor corresponds to de Sitter vacuum everywhere outside of the black holes except at the equator where we match the black hole spacetimes, where a shell with positive energy density appears. We discuss the physical relevance of this solution in various contexts, including the cosmological constant problem.

Speeding up the Universe using dust with pressure

We revise the cosmological standard model presuming that matter, i.e. baryons and cold dark matter, exhibits a non-vanishing pressure mimicking the cosmological constant effects. In particular, we propose a scalar field Lagrangian $\mathcal L_1$ for matter with the introduction of a Lagrange multiplier as constraint. We also add a symmetry breaking effective potential accounting for the classical cosmological constant problem, by adding a second Lagrangian $\mathcal{L}_2$. Investigating the Noether current due to the shift symmetry on the scalar field, $\varphi\rightarrow\varphi+c^0$, we show that $\mathcal{L}_1$ turns out to be independent from the scalar field $\varphi$. Further we find that a positive Helmotz free-energy naturally leads to a negative pressure without introducing by hand any dark energy term. To face out the fine-tuning problem, we investigate two phases: before and after transition due to the symmetry breaking. We propose that during transition dark matter cancels out the quantum field vacuum energy effects. This process leads to a negative and constant pressure whose magnitude is determined by baryons only. The numerical bounds over the pressure and matter densities are in agreement with current observations, alleviating the coincidence problem. Finally assuming a thermal equilibrium between the bath and our effective fluid, we estimate the mass of the dark matter candidate. Our numerical outcomes seem to be compatible with recent predictions on WIMP masses, for fixed spin and temperature. In particular, we predict possible candidates whose masses span in the range $0.5-1.7$ TeV.

On a physical description and origin of the cosmological constant

In this paper we use and extend the results present in Viaggiu (2017 Physica A 473 412, 2017 Physica A 488 72, 2018 Int. J. Mod. Phys. D 27 1850061, 2018 Int. J. Mod. Phys. A 33 1850074) and in particular in Viaggiu (2018 Int. J. Mod. Phys. A 33 1850074) to obtain a statistical description of the cosmological constant in a cosmological de Sitter universe in terms of massless excitations with Planckian effects. First of all, we show that at a classical level, the cosmological constant can be obtained only for . Similar to the black hole case, when quantum effects are taken into account, a representation for Λ is possible in terms of massless excitations, provided that quantum corrections to the Misner–Sharp mass are considered. Moreover, thanks to quantum fluctuations, an effective cosmological constant arises depending on the physical scale under consideration, thus representing a possible solution to the cosmological constant problem without introducing a quintessence field. The smallness of the actual value for Λ can be due to the existence of a quantum decoherence scale above the Planck length such that the spacetime evolves as a pure de Sitter universe with a small averaged cosmological constant frozen in the lowest energy state.

Conformal symmetry and the cosmological constant problem

We argue that when a theory of gravity and matter is endowed with (classical) conformal symmetry, the fine tuning required to obtain the cosmological constant at its observed value can be significantly reduced. Once tuned, the cosmological constant is stable under a change of the scale at which it is measured.

Can the fluctuations of the quantum vacuum solve the cosmological constant problem?

The cosmological constant problem arises because the magnitude of vacuum energy density predicted by quantum mechanics is about 120 orders of magnitude larger than the value implied by cosmological observations of accelerating cosmic expansion. Recently, some of the current authors proposed that the stochastic nature of the quantum vacuum can resolve this tension [Q, Wang, Z. Zhu, and W. G. Unruh, Phys. Rev. D 95, 103504, 2017]. By treating the fluctuations in the vacuum seriously and allowing fluctuations up to some high-energy cutoff at which Quantum Field Theory is believed to break down, a parametric resonance effect arises that leads to a slow expansion and acceleration. In this work, we thoroughly examine the implications of this proposal by investigating the resulting dynamics. First, we improve upon numerical calculations in the original work and show that convergence issues had overshadowed some important effects. Correct calculations reverse some of the conclusions in [Q. Wang, Z. Zhu, and W. G. Unruh, Phys. Rev. D 95, 103504, 2017], however the premise that parametric resonance can explain a very slowly accelerating expansion appears to remain sound. After improving the resolution and efficiency of the numerical tests, we explore a wider range of cutoff energies, and examine the effects of multiple particle fields. We introduce a simple model using the Mathieu equation (a prototypical example of parametric resonance), and find that it closely matches numerical results in regimes where its assumptions are valid. Using this model, we extrapolate to find that in a universe with 28 bosonic fields and a high-energy cutoff 40 times higher than the Planck energy, the acceleration would be comparable to what is observed.

Absence of cosmological constant problem in special relativistic field theory of gravity

The principles of quantum field theory in flat spacetime suggest that gravity is mediated by a massless particle with helicity ±2, the so-called graviton. It is regarded as textbook knowledge that, when the self-coupling of a particle with these properties is considered, the long-wavelength structure of such a nonlinear theory is fixed to be that of general relativity. However, here we indicate that these arguments conceal an implicit assumption which is surreptitiously motivated by the very knowledge of general relativity. This is shown by providing a counterexample: we revisit a nonlinear theory of gravity which is not structurally equivalent to general relativity and that, in the non-interacting limit, describes a free helicity ±2 graviton. We explicitly prove that this theory, known as Weyl-transverse gravity (unimodular gravity with explicit Weyl invariance), can be understood as the result of self-coupling in complete parallelism to the well-known case of general relativity. We discuss the absence of cosmological constant problem in this theory, highlighting that it provides a particular realization of previous arguments formulated in studies of the emergence of the gravitational interaction from condensed-matter-like models. Overall, we conclude that the consideration that gravity is mediated by a massless particle with helicity ±2 does not inextricably lead to the cosmological constant problem.

From de Sitter to de Sitter: Decaying Vacuum Models as a Possible Solution to the Main Cosmological Problems

Decaying vacuum cosmological models evolving smoothly between two extreme (very early and late time) de Sitter phases are able to solve or at least to alleviate some cosmological puzzles; among them we have (i) the singularity, (ii) horizon, (iii) graceful-exit from inflation, and (iv) the baryogenesis problem. Our basic aim here is to discuss how the coincidence problem based on a large class of running vacuum cosmologies evolving from de Sitter to de Sitter can also be mollified. It is also argued that even the cosmological constant problem becomes less severe provided that the characteristic scales of the two limiting de Sitter manifolds are predicted from first principles.