GW Production Research Articles

Axion-gauge dynamics during inflation as the origin of pulsar timing array signals and primordial black holes

We demonstrate that the recently announced signal for a stochastic gravitational wave background (SGWB) from pulsar timing array (PTA) observations, if attributed to new physics, is compatible with primordial GW production due to axion-gauge dynamics during inflation. More specifically we find that axion-U(1) models may lead to sufficient particle production to explain the signal while simultaneously source some fraction of sub-solar mass primordial black holes (PBHs) as a signature. Moreover there is a parity violation in GW sector, hence the model suggests chiral GW search as a concrete target for future. We further analyze the axion-SU(2) coupling signatures and find that in the low/mild backreaction regime, it is incapable of producing PTA evidence and the tensor-to-scalar ratio is low at the peak, hence it overproduces scalar perturbations and PBHs.

Comments: Economic Realities of Energy Transition

No one expected the energy transition to be without hiccups, and recently, those hiccups have been heard within and outside the oil and gas industry. Daniel Yergin, vice chairman of S&P Global and author of several books, wrote how previous energy transitions evolved over the course of a century or more and did not “wholly displace the incumbent technologies.” Oil became the world’s No. 1 energy source in the 1960s, bumping coal from the top. “ … Yet we now use three times more coal than we did back then, with global consumption hitting a record high in 2022,” he noted. He continued, “By contrast, today’s transition is intended to unfold in little more than a quarter century and not be additive.” Yergin cited a 2021 paper by Jean Pisani-Ferry, an economist at the Peterson Institute for International Economics, who wrote that moving too rapidly to net-zero emissions could precipitate “an adverse supply shock—very much like the shocks of the 1970s” and that it “is unlikely to be benign and policymakers should get ready for tough choices.” The outcome of those tough choices is becoming evident, both in policy and companies’ actions. For example, Equinor put an indefinite hold on its plans for a floating offshore wind farm, Trollvind. Initially planned to have an installed capacity of about 1 GW and annual production of 4.3 TWh, the electricity was to be used to run the Troll and Oseberg fields. The operator cited “challenges facing the broader offshore wind industry,” including how rising costs changed its original view that Trollvind would not require any financial support. “It is no longer a commercially sustainable project,” Equinor said in a statement. It added that the unavailability of preferred technology made the concept less viable and that the proposed timeline was not achievable to the level required to go forward. Shell recently pulled out of the Northern Endurance Partnership, Britain’s CCS project targeting industrial decarbonization. Another equity holder, National Grid, also withdrew from the project, dropping its plans to construct pipelines to transport the CO2 to the North Sea. The equity holdings were acquired by the remaining project partners, BP, Equinor, and TotalEnergies. The need for return on investments (ROI) was highlighted in a survey of global energy and natural resource executives by Bain & Co. in May. The responses showed executives believe their companies are outperforming the rest of the world in reducing emissions but expect the rate of decarbonization to slow down over the next few years. The surveyed companies expect to deploy about a quarter of their capital on new growth businesses in 2023, many of these focusing on low‑carbon technologies. The executives aren’t concerned about accessing capital for low-carbon businesses, but “need to ensure adequate returns on the investments.” Four out of five executives considered the ability to create acceptable returns on projects a main barrier to decarbonization. Customers demonstrate an unwillingness to pay—not universally, “but enough to make it hard to scale low‑ carbon businesses.” They look to government policy and regulatory support to help bridge the gap. Complicating ROI is how it is perceived in the eye of the investor. What investors value is not limited to the dividends they may receive. Individual and institutional investors are increasingly paying attention to ESG (environmental, social, and governance) criteria. Norway’s $1.4 trillion wealth fund, which invests Norwegian state revenues from oil and gas production, on 26 May said it would vote for shareholder proposals at Chevron and ExxonMobil to adopt a medium‑term Scope 3 greenhouse gas (GHG) reduction target. Scope 3 refers to emissions not produced by the company itself or from its owned or controlled assets, but those it is indirectly responsible for, up and down its value chain. Last year, the fund said it would push the companies it invests in to cut GHG emissions to net zero by 2050, in line with the Paris Agreement. It emphasized that it would not divest from big emitters to achieve these targets and would instead be an “active shareholder” to effect change. “The easy way to cut down emissions is to sell out,” fund CEO Nicolai Tangen said. “But someone needs to own these companies and it does not solve the problem, quite the contrary.” When Shell CEO Wael Sawan discussed the company’s 2022 record profits of $39 billion, he said, “Profit without sustainability erodes our license to operate. Sustainability without profit erodes our shareholder support and financial capacity to play a meaningful part in the energy transition. We must continue to provide energy and do it with fewer emissions. We can only do this with the backing of our shareholders because it is their capital that enables us to invest in the energy transition.”

Post-inflationary GW production in generic higher (infinite) derivative gravity

Gravity can be embedded into a renormalizable theory by means of adding quadratic in curvature terms. However, this at first leads to the presence of the Weyl ghost. It is possible to get rid of this ghost if the locality assumption is weakened and the propagator of the graviton is represented by an entire function of the d'Alembertian operator without new poles and zeros. Models of this type admit a cosmological solution describing the R2, or Starobinsky, inflation. We study graviton production after inflation in this model and show that it is negligible despite the presence of the higher derivative operators which could potentially cause instabilities.

Audible axions with a booster: Stochastic gravitational waves from rotating ALPs

Gravitational waves provide a novel way to probe axions or axion-like particles coupled to a dark photon field, even in the absence of couplings to Standard Model particles. In the conventional misalignment mechanism, the generation of an observable stochastic gravitational wave background, however, requires large axion decay constants. We here investigate the gravitational wave signal generated within the kinetic misalignment scenario, where the axion is assumed to have a large initial velocity. Its kinetic energy then provides a sufficiently high energy budget to generate a detectable gravitational wave signal also at lower values of the decay constant. We obtain an analytic estimate as well as perform numerical simulations of the corresponding gravitational wave signal, and evaluate its detectability at current and future gravitational wave observatories. We further present the corresponding projected constraints on the parameter space of the model, along with the parameter regions in which the dark photon or axion constitute dark matter, or in which the baryon asymmetry of the Universe is generated via the axiogenesis mechanism. Finally, we compute the GW production from the fragmentation of rotating axions, which is however difficult to observe experimentally.

Relativistic viscous effects on the primordial gravitational waves spectrum

We study the impact of the viscous effects of the primordial plasma on the evolution of the primordial gravitational waves (pGW) spectrum from Inflation until today, considering a self-consistent interaction that incorporates the back-reaction of the GW into the plasma. We use a relativistic causal hydrodynamic framework with a positive entropy production based on a Second-Order Theory (SOT) in which the viscous properties of the fluid are effectively described by a new set of independent variables. We study how the spin-2 modes typical of SOTs capture the simplest GW-fluid viscous interaction to first order. We consider that all non-ideal properties of the primordial plasma are due to an extra effectively massless self-interacting scalar field whose state becomes a many-particles one after Reheating and for which an effective fluid description is suitable. We numerically solve the evolution equations and explicitly compute the current GW spectrum obtaining two contributions. On the one hand we have the viscous evolution of the pGW: for the collision-dominated regime the GW source becomes negligible while in the collisionless limit there exists an absorption of the pGW energy due to the damping effect produced by the free-streaming spin-2 modes of the fluid and driven by the expansion of the Universe. The latter effect is characterized by a relative amplitude decrease of about 1 to 10 % with respect to the GW free evolution spectrum. On the other hand we get the GW production due to the decay of the initial spin-2 fluctuations of the fluid that is negligible compared with the above-mentioned contribution.This SOT framework captures the same qualitative effects on the evolution of GW coupled to matter reported in previous works in which a kinetic theory approach has been used.

Bridging the gap: spectral distortions meet gravitational waves

ABSTRACT Gravitational waves (GWs) have the potential to probe the entirety of cosmological history due to their nearly perfect decoupling from the thermal bath and any intervening matter after emission. In recent years, GW cosmology has evolved from merely being an exciting prospect to an actively pursued avenue for discovery, and the early results are very promising. As we highlight in this paper, spectral distortions (SDs) of the cosmic microwave background (CMB) uniquely probe GWs over six decades in frequency, bridging the gap between astrophysical high- and cosmological low-frequency measurements. This means SDs will not only complement other GW observations, but will be the sole probe of physical processes at certain scales. To illustrate this point, we explore the constraining power of various proposed SD missions on a number of phenomenological scenarios: early-universe phase transitions (PTs), GW production via the dynamics of SU(2) and ultralight U(1) axions, and cosmic string (CS) network collapse. We highlight how some regions of parameter space were already excluded with data from COBE/FIRAS , taken over two decades ago. To facilitate the implementation of SD constraints in arbitrary models, we provide GW2SD. This tool calculates the window function, which easily maps a GW spectrum to an SD amplitude, thus opening another portal for GW cosmology with SDs, with wide reaching implications for particle physics phenomenology.

First Principal Treatment of Size of Inflaton Potential, Inflaton Mass, Scale Factors, and Frequency of Emitted Radiation, Using Linde and Padmanabhan Models of Early Cosmology and BEC

Using a Linde reference, as well as another one from Padmanabhan for calculation of how the early universe expands, we obtain, by default the coefficient of scale factor expansion, t to the alpha value, with alpha being approximately the square root of five in value. We from there make an estimate as to the number of initial particles produced in the very beginning, which leads us to conclude that a graviton, would be a preferred initial by product. The argument as to gravitons, also reflects a choice of how the decay of initial BEC condensates of Planck sized black holes would commence, using the work produced by Chavanis, as to BEC condensates and black holes. The object will be to obtain initial frequency spread plus strength of GW production plus a suggestion as to what polarization state may be accessible from initial conditions.

Does the Penrose Suggestion as to Black Holes from a Prior Universe Showing Up in Today’s Universe Have Credibility? Examined from a Singular, and Nonsingular Beginning of Cosmological Expansion

We examine if there are grounds to entertain the Penrose suggestion as to black holes from a prior cycle of creation appearing in the present cosmos. There are two cases to consider. One a singular start to the Universe or as Karen Freeze and others have modeled a non-singular start. The two cases are different and touch upon the limits of validity of the Penrose singularity theorem. We will first of all state the two cases, singular and nonsingular, and then afterwards, briefly allude to the Penrose singularity theorem. The plausibility of the singular cosmological expansion start point w case analysis of Black holes from a prior universe will be discussed first Afterwards, a synopsis of the Penrose singularity theorem. After that, the Nonsingular case of a starting point of the expansion of the Universe will be entertained and described. Since the nonsingular start to the expansion of the Universe is not so well known, a considerable amount of space will be spent upon what I view as mathematical constructions allowing for its analysis. About the only way to ascertain these cases will be by GW astronomy, hence the details of GW production from the early Universe will be covered in excruciating detail. The methodology for that section is simple. Use a construction for a minimal time-step, then from there get emergent space-time conditions for a bridge from a nonsingular start to the universe, to potential Quantum gravity conditions. Our Methodology is to construct using a “trivial” solution to massive gravitons, and a nonsingular start for expansion of the universe. Our methodology has many unintended consequences, not the least is a relationship between a small timestep, which is called t, and then the minimum scale factor and even the tension or property values of the initial space-time wall, all of which are a consequence of a “trivial” solution taking into account “massive” gravitons. From there we next will in future articles postulate conditions for experimental detectors for subsequent data sets to obtain falsifiable data sets. Finally upon doing this, the outlines of the way to ascertain data sets as to either falsify or confirm the Penrose suggestion will be the final concluding part of the manuscript.

How a Laser Physics Induced Kerr-Newman Black Hole Can Release Gravitational Waves without Igniting the Black Hole Bomb (Explosion of a Mini Black Hole in a Laboratory)

Note, that micro black holes last within micro seconds, and that we wish to ascertain how to build, in a laboratory, a black hole, which may exist say at least up to 10^−1 seconds and provide a test bed as to early universe gravitational theories. First of all, it would be to determine, if the mini black hole bomb, would spontaneously occur, unless the Kerr-Newmann black hole were carefully engineered in the laboratory. Specifically, we state that this paper is modeling the creation of an actual Kerr Newman black hole via laser physics, or possibly by other means. We initiate a model of an induced Kerr-Newman black Holes, with specific angular momentum J, and then from there model was to what would happen as to an effective charge, Q, creating an E and B field, commensurate with the release of GWs. The idea is that using a frame of reference trick, plus E + i B = −function of the derivative of a complex valued scalar field, as given by Appell, in 1887, and reviewed by Whittaker and Watson, 1927 of their “A Course of Modern Analysis” tome that a first principle identification of a B field, commensurate with increase of thermal temperature, T, so as to have artificially induced GW production. This is compared in part with the Park 1955 paper of a spinning rod, producing GW, with the proviso that both the spinning rod paper, and this artificial Kerr-Newman Black hole will employ the idea of lasers in implementation of their respective GW radiation. The idea is in part partly similar to an idea the author discussed with Dr. Robert Baker, in 2016 with the difference that a B field would be generated and linked to effects linked with induced spin to the Kerr-Newman Black hole. We close with some observations about the “black holes have no hair” theorem, and our problem. Citing some recent suppositions that this “theorem” may not be completely true and how that may relate to our experimental situation. We close with observations from Haijicek, 2008 as which may be pertinent to Quantization of Gravity. Furthermore as an answer to questions raised by a referee, we will have a final statement as to how this problem is for a real black hole being induced, and answering his questions in his review, which will be included in a final appendix to this paper. The main issue which is now to avoid the black hole bomb effect which would entail an explosion of a small black hole in a laboratory. Furthermore as an answer to questions raised by a referee, we will have a final statement as to how this problem is for a real black hole being induced, and answering his questions in his review, which will be included in a final appendix to this paper. In all, the main end result is to try to avoid the so called black hole bomb effect, where a mini black hole would explode in a laboratory setting within say 10^−16 or so seconds, i.e. the idea would be to have a reasonably stable configuration within put laser energy, but a small mass, and to do it over hopefully 10^15 or more times longer than the 10^−16 seconds where the mini black hole would quickly evaporate. I.e. a duration of say up to 10^−1 seconds which would provide a base line as to astrophysical modeling of a Kerr-Newman black hole.

Gravitational radiation from massless particle collisions

We compute classical gravitational bremsstrahlung from the gravitational scattering of two massless particles at leading order in the (centre of mass) deflection angle . The calculation, although non-perturbative in the gravitational constant, is surprisingly simple and yields explicit formulae—in terms of multidimensional integrals—for the frequency and angular distribution of the radiation. In the range , the GW spectrum behaves like , is confined to cones of angular sizes (around the deflected particle trajectories) ranging from to , and exactly reproduces, at its lower end, a well-known zero-frequency limit. At the radiation is confined to cones of angular size of order resulting in a scale-invariant () spectrum. The total efficiency in GW production is dominated by this ‘high frequency’ region and is formally logarithmically divergent in the UV. If the spectrum is cutoff at the limit of validity of our approximations (where a conjectured bound on GW power is also saturated), the fraction of incoming energy radiated away turns out to be at leading logarithmic accuracy.

Gravitational waves and scalar perturbations from spectator fields

The most conventional mechanism for gravitational waves (gw) production during inflation is the amplification of vacuum metric fluctuations. In this case the gw production can be uniquely related to the inflationary expansion rate H. For example, a gw detection close to the present experimental limit (tensor-to-scalar ratio r ∼ 0.1) would indicate an inflationary expansion rate close to 1014 GeV. This conclusion, however, would be invalid if the observed gw originated from a different source. We construct and study one of the possible covariant formulations of the mechanism suggested in [1], where a spectator field σ with a sound speed cs ≪ 1 acts as a source for gw during inflation. In our formulation σ is described by a so-called P(X) Lagrangian and a non-minimal coupling to gravity. This field interacts only gravitationally with the inflaton, which has a standard action. We compute the amount of scalar and tensor density fluctuations produced by σ and find that, in our realization, r is not enhanced with respect to the standard result but it is strongly sensitive to cs, thus breaking the direct r ↔ H connection.

Rump Session: Science and technologies which support production of CIS solar cells and modules

CuInGaSe2 (CIGS) solar cells have shown high conversion efficiencies of as high as η = 19.5%, and several companies (Showa Shell Sekiyu, Honda, Wuerth Solar) announced to start the commercial production of 15–30 MW/year in 2007. In this session, scientific and technological issues which can support the production of CIGS solar cells and modules have been discussed. After the introduction of current conditions of research and development of CIGS solar cells and modules as well as of the Japanese PV roadmap for 2030, four panellists presented about the scientific and technical issues important for production of CIGS modules in order to further improve the performance and cost of CIGS modules. In the discussion session, possibilities of over 20% solar cells and over 1 GW production have been extensively discussed. Basic and focused research on material characterization, thin film growth, chemical reaction, etc., was agreed by all the participants to lead to the promotion of the mass-production of CIGS modules. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)