Cosmological Vacuum Energy Research Articles

ASKING IF VACUUM ENERGY allows COMPUTATIONAL “BITS” PRESENT AT START OF COSMOLOGICAL EVOLUTION, and its possible ties into torsion physics

Based on Torsion as given by de Sabbata and Sirvaram, Erice 1990 . The 1990 article claims that Torsion cancels Cosmological vacuum energy. We consider if relic black holes at the start of inflation may allow for the observed cosmological constant. Using the 1990 text if thermal energy is used at start of inflation creates conceptual issues, whereas an energy term based on Corda’s treatment of black holes may provide a solution. i.e. a left over cosmological constant 10^-121 times vacuum energy . Considerations as to how black hole physics may contribute to torsion and the cosmological constant are considered in several numerical cases Also we present entanglement entropy in the early universe with a shrinking scale factor, due to Muller and Lousto , and show that there are consequences due to initial entanged for a time dependent horizon radius in cosmology, with (flat space conditions) for conformal time . This construction preserves a minimum non zero vacuum energy, and in doing so keep the bits, for computational bits cosmological evolution. The bits are ascribed to initial torsion for reasons which we elaborate on in this manuscript

The role of gravity in naturalness versus consistency: strong- CP and dark energy

There is an ongoing debate on how seriously one should take the naturalness puzzles as the guidelines to new physics. In this debate gravity is often put aside, as an insignificant spectator force. However, this attitude misses the entire essence of the story. Through its S -matrix formulation, gravity promotes certain puzzles, such as the cosmological constant and strong- C P problems, into the consistency issues. The respective consistency requirements make the theory highly predictive. In particular, the cosmological vacuum energy must be zero. This has fundamental implications both for strong- C P and for dark energy puzzles. QCD must include an axion as an intrinsic part of the gauge redundancy, without the need of any global symmetry. This gives ϑ ¯ = 0 to all orders in operator expansion. Applied to cosmology, the S -matrix implies that the energy budget of the Universe cannot come from a constant. Correspondingly, the dark energy is an unambiguous signal of new physics around the Hubble scale. This article is part of the theme issue ‘The particle-gravity frontier’.

Vacuum Energy, the Casimir Effect, and Newton’s Non-Constant

The idea of quantum mechanical vacuum energy contributing to the cosmological vacuum energy density is not new. However, despite the persisting cosmological constant problem, few investigations have focused on this subject. We explore the possibility that the quantum vacuum energy density contributes to the (local) gravitational energy density in the framework of a scale-dependent cosmological constant Λ and Newton’s constant G. This hypothesis has several important consequences, ranging from quantum scale-dependence to the hypothetical prospect of novel experimental insight concerning the quantum origin of cosmological energy density.

Solving the Problem of the Cosmological Constant and Vacuum Energy Density by Considering the Cosmic Quantum Number

Solving the Problem of the Cosmological Constant and Vacuum Energy Density by Considering the Cosmic Quantum Number

Aspects of nonperturbative GUP models

We review on further new developments of Generalized Uncertainty Principle (GUP) and implications for the cosmological vacuum energy. First, we introduce basic aspects of GUP as well as several possible different and viable formulation of it. Second, we move on discussing two recent new types of higher D-dimensional nonperturbative GUP models; which we dub D-Type-I and D-Type-II GUPs. The D-Type-I and D-Type-II GUPs are both related to the existence of a critical conspiracy between a minimal uncertainty length and a maximal observable momentum. Finally, we show direct implications of D-Type-I and D-Type-II on the cosmological vacuum energy obtained in quantum mechanical systems such as the typical quantum harmonic oscillator. Such a computation goes through investigations of the density of states for D-dimensional coordinate systems in the momentum space. We will also comment on several possible connections with fundamental issues of quantum gravity such as black hole physics and gravitational radiative aspects.

Inflation without a trace of lambda

We generalise Einstein’s formulation of the traceless Einstein equations to f(R) gravity theories. In the case of the vacuum traceless Einstein equations, we show that a non-constant Weyl tensor leads via a conformal transformation to a dimensionally homogeneous (‘no-scale’) theory in the conformal frame with a scalar field source that has an exponential potential. We then formulate the traceless version of f(R) gravity, and we find that a conformal transformation leads to a no-scale theory conformally equivalent to general relativity and a scalar field phi with a potential given by the scale-invariant form: V(phi )=frac{D-2}{4D}Re^{-phi }, where phi =[2/(D-2)]ln f^{prime }(R). In this theory, the cosmological constant is a mere integration constant, statistically distributed in a multiverse of independent causal domains, the vacuum energy is another unrelated arbitrary constant, and the same is true of the height of the inflationary plateau present in a huge variety of potentials. Unlike in the conformal equivalent of full general relativity, flat potentials are found to be possible in all spacetime dimensions for polynomial lagrangians of all orders. Hence, we are led to a novel interpretation of the cosmological constant vacuum energy problem and have accelerated inflationary expansion in the very early universe with a very small cosmological constant at late times for a wide range of no-scale theories. Fine-tunings required in traceless general relativity or standard non-traceless f(R) theories of gravity are avoided. We show that the predictions of the scale-invariant conformal potential are completely consistent with microwave background observational data concerning the primordial tilt and the tensor-to-scalar ratio.

Motion of spinning particles in non asymptotically flat spacetimes

The assumption of asymptotic flatness for isolated astrophysical bodies may be considered an approximation when one considers a cosmological context where a cosmological constant or vacuum energy is present. In this framework we study the motion of spinning particles in static, spherically symmetric and asymptotically non-flat spacetimes with repulsive cosmological vacuum energy and quintessential field. Due to the combined effects of gravitational attraction and cosmological repulsion, the region where stable circular orbits are allowed is restricted by an innermost and an outermost stable circular orbits. We show that taking into account the spin of test particles may enlarge or shrink the region of allowed stable circular orbits depending on whether the spin is co-rotating or counter-rotating with the angular momentum of the particles.

The size of our causal Universe

ABSTRACT 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.

Brans–Dicke gravity: From Higgs physics to (dynamical) dark energy

The Higgs mechanism is one of the central pieces of the Standard Model of electroweak interactions and thanks to it we can generate the masses of the elementary particles. Its fundamental origin is nonetheless unknown. Furthermore, in order to preserve renormalizability, we have to break the gauge symmetry spontaneously, which leads to a huge induced cosmological constant incompatible with observations. It turns out that in the context of generalized Brans–Dicke theories of gravity, the Higgs potential structure can be motivated from solutions of the field equations which carry harmless cosmological vacuum energy. In addition, the late-time cosmic evolution effectively appears like a universe filled with mildly evolving dynamical dark energy mimicking quintessence or phantom dark energy.

Superfluids and the cosmological constant problem

We introduce a novel method to circumvent Weinberg's no-go theorem for self-tuning the cosmological vacuum energy: a finite-temperature superfluid can counter the effects of an arbitrarily large cosmological constant. Fluctuations of the superfluid result in the graviton acquiring a Lorentz-violating mass and we identify a unique class of theories that are pathology free, phenomenologically viable, and do not suffer from instantaneous modes. This new and hitherto unidentified phase of massive gravity propagates the same degrees of freedom as general relativity with an additional Lorentz-violating scalar that is introduced by higher-derivative operators in a UV insensitive manner. The superfluid is therefore a consistent infrared modification of gravity. We demonstrate how the superfluid can degravitate a cosmological constant and discuss its phenomenology.

Non Linear Electrodynamics Contributing to a Minimum Vacuum Energy (“Cosmological Constant”) Allowed in Early Universe Cosmology

This article poses the question of a minimum cosmological constant, i.e. vacuum energy at the start of the cosmological evolution from a near singularity. We pose this comparing formalism as given by Berry (1976) as to a small time length, and compare that in its entirety to compare this value given by Berry (1976) with a minimum time length at the start of cosmological space-time evolution. Using the methodology of Zeldovich (1972) as to a problem with electron-positron pair production we also propose another upper bound to the problem of minimum time length which may be accessible to experimental inquiry. This then makes the problem of minimum time length a way of specifying a magnetic field dependence of the cosmological constant, which has major implications to answering if quintessence, i.e. a changing cosmological vacuum energy, or a constant for the “cosmological constant” problem. Our answer is an initial value for the cosmological vacuum energy 1010 - 1020 times greater than today which suggests either Quintessence, or if still a constant, a much better value for this parameter than what is suggested by traditional field theory methods. In closing we review how our construct supports work done by Corda, as to early universe models and what the implications are, as to the choices we have made.

Vacuum energy and the cosmological constant

The accelerating expansion of the Universe points to a small positive value for the cosmological constant or vacuum energy density. We discuss recent ideas that the cosmological constant plus Large Hadron Collider (LHC) results might hint at critical phenomena near the Planck scale.

INCONSISTENCIES FROM A RUNNING COSMOLOGICAL CONSTANT

We examine the general issue of whether a scale dependent cosmological constant can be consistent with general covariance, a problem that arises naturally in the treatment of quantum gravitation, where coupling constants generally run as a consequence of renormalization group effects. The issue is approached from several points of view, which include the manifestly covariant functional integral formulation, covariant continuum perturbation theory about two dimensions, the lattice formulation of gravity, and the nonlocal effective action and effective field equation methods. In all cases we find that the cosmological constant cannot run with scale, unless general covariance is explicitly broken by the regularization procedure. Our results are expected to have some bearing on current quantum gravity calculations, but more generally should apply to phenomenological approaches to the cosmological vacuum energy problem.

Cosmological constant and vacuum energy: old and new ideas

The cosmological constant (CC) term in Einstein's equations, Λ, was first associated to the idea of vacuum energy density. Notwithstanding, it is well-known that there is a huge, in fact appalling, discrepancy between the theoretical prediction and the observed value picked from the modern cosmological data. This is the famous, and extremely difficult, "CC problem". Paradoxically, the recent observation at the CERN Large Hadron Collider of a Higgs-like particle, should actually be considered ambivalent: on the one hand it appears as a likely great triumph of particle physics, but on the other hand it wide opens Pandora's box of the cosmological uproar, for it may provide (alas!) the experimental certification of the existence of the electroweak (EW) vacuum energy, and thus of the intriguing reality of the CC problem. Even if only counting on this contribution to the inventory of vacuum energies in the universe, the discrepancy with the cosmologically observed value is already of 55 orders of magnitude. This is the (hitherto) "real" magnitude of the CC problem, rather than the (too often) brandished 123 ones from the upper (but fully unexplored!) ultrahigh energy scales. Such is the baffling situation after 96 years of introducing the Λ-term by Einstein. In the following I will briefly (and hopefully pedagogically) fly over some of the old and new ideas on the CC problem. Since, however, the Higgs boson just knocked our door and recalled us that the vacuum energy may be a fully tangible concept in real phenomenology, I will exclusively address the CC problem from the original notion of vacuum energy, and its possible "running" with the expansion of the universe, rather than venturing into the numberless attempts to replace the CC by the multifarious concept of dark energy.

Surface vacuum energy in cutoff models: pressure anomaly and distributional gravitational limit

Vacuum-energy calculations with ideal reflecting boundaries are plagued by boundary divergences, which presumably correspond to real (but finite) physical effects occurring near the boundary. Our working hypothesis is that the stress tensor for idealized boundary conditions with some finite cutoff should be a reasonable ad hoc model for the true situation. The theory will have a sensible renormalized limit when the cutoff is taken away; this requires making sense of the Einstein equation with a distributional source. Calculations with the standard ultraviolet cutoff reveal an inconsistency between energy and pressure similar to the one that arises in noncovariant regularizations of cosmological vacuum energy. The problem disappears, however, if the cutoff is a spatial point separation in a ‘neutral’ direction parallel to the boundary. Here we demonstrate these claims in detail, first for a single flat reflecting wall intersected by a test boundary, then more rigorously for a region of finite cross section surrounded by four reflecting walls. We also show how the moment-expansion theorem can be applied to the distributional limits of the source and the solution of the Einstein equation, resulting in a mathematically consistent differential equation where cutoff-dependent coefficients have been identified as renormalizations of properties of the boundary. A number of issues surrounding the interpretation of these results are aired.

Dynamical vacuum energy and phantom divide-line cross in scalar cosmology

In this paper, we study cosmological models in scalar tensor theory of gravity a la Brans–Dicke with a dynamical equation of state parameter, a dynamical effective cosmological constant and a Hubble parameter varying like \( H = \varepsilon t^{s} + H_{0} \) with \( \varepsilon \) and \( H_{0} \) are real positive parameters and \( s \) is some pending power index. It is observed that the universe is accelerating in time and it is dominated by a decreasing energy density and a vacuum energy density. However the vacuum energy density is increasing logarithmically at early epoch of time and then decaying toward its present positive value at late-time epoch. For specific choices of the free parameters in the theory, it is observed that the phantom divide line is crossed in the presence of a cosmological constant and the universe expands asymptotically a la de-Sitter at very large time. Additional features are discussed as well.

Spontaneous symmetry breaking vacuum energy in cosmology

The gravitational effect of spontaneous symmetry breaking vacuum energy density is investigated by subtracting the flat space—time contribution from the energy in the curved space—time. We find that the remaining effective energy—momentum tensor is too small to cause the acceleration of the universe, although it satisfies the characteristics of dark energy. However, it could provide a promising explanation to the puzzle of why the gravitational effect produced by the huge symmetry breaking vacuum energy in the electroweak theory has not been observed, as it has a sufficiently small value (smaller than the observed cosmic energy density by a factor of 1032).

Cosmology and elementary particles, or celestial mysteries

This is an extended version of the report at Round Table 2, Italy-Russia Dubna “Space Physics and Biology.” Given the diversity of the audience, this paper provides a popular description of the cosmological problems which can be solved only by introduction of new phenomena beyond the minimal standard model of particle physics. The cosmological dark and vacuum energy, dark matter, inflation, and baryogenesis are discussed. In the conclusion, possibilities for a fundamental change in the laws of modern physics are briefly discussed.

CASTING LIGHT ON THE GHOST

The infrared sector of QCD contains all the necessary ingredients, once laid onto a time-dependent, curved background, to cater for the much needed cosmological vacuum energy. This is achieved through the fields that describe the impact of the long-range interactions of QCD, the Veneziano ghost and its dipolar partner. Although technically extremely challenging, the physics is well understood and the estimated dark energy density is of the correct order of magnitude. In this brief review I will retrace the steps leading to two new cosmological applications of this model, namely the possibility of the generation of cosmic magnetic fields, and the unification of several observed polarization anomalies under the same roof.

Large-scale magnetic fields, dark energy, and QCD

Cosmological magnetic fields are being observed with ever increasing correlation lengths, possibly reaching the size of superclusters, therefore disfavoring the conventional picture of generation through primordial seeds later amplified by galaxy-bound dynamo mechanisms. In this paper we put forward a fundamentally different approach that links such large-scale magnetic fields to the cosmological vacuum energy. In our scenario the dark energy is due to the Veneziano ghost (which solves the $U(1{)}_{A}$ problem in QCD). The Veneziano ghost couples through the triangle anomaly to the electromagnetic field with a constant which is unambiguously fixed in the standard model. While this interaction does not produce any physical effects in Minkowski space, it triggers the generation of a magnetic field in an expanding universe at every epoch. The induced energy of the magnetic field is thus proportional to cosmological vacuum energy: ${\ensuremath{\rho}}_{\mathrm{EM}}\ensuremath{\simeq}{B}^{2}\ensuremath{\simeq}(\frac{\ensuremath{\alpha}}{4\ensuremath{\pi}}{)}^{2}{\ensuremath{\rho}}_{\mathrm{DE}}$, ${\ensuremath{\rho}}_{\mathrm{DE}}$ hence acting as a source for the magnetic energy ${\ensuremath{\rho}}_{\mathrm{EM}}$. The corresponding numerical estimate leads to a magnitude in the nG range. There are two unique and distinctive predictions of our proposal: an uninterrupted active generation of Hubble size correlated magnetic fields throughout the evolution of the Universe; the presence of parity violation on the enormous scales $1/H$, which apparently has been already observed in CMB. These predictions are entirely rooted into the standard model of particle physics.