Testing Emergent Gravity on Galaxy Cluster Scales

Verlinde's theory of Emergent Gravity (EG) describes gravity as an emergent phenomenon rather than a fundamental force. Applying this reasoning in de Sitter space leads to gravity behaving differently on galaxy and galaxy cluster scales; this excess gravity might offer an alternative to dark matter. Here we test these ideas using the data from the Coma cluster and from 58 stacked galaxy clusters. The X-ray surface brightness measurements of the clusters at $0.1 < z < 1.2$ along with the weak lensing data are used to test the theory. We find that the simultaneous EG fits of the X-ray and weak lensing datasets are significantly worse than those provided by General Relativity (with cold dark matter). For the Coma cluster, the predictions from Emergent Gravity and General Relativity agree in the range of 250 - 700 kpc, while at around 1 Mpc scales, EG total mass predictions are larger by a factor of 2. For the cluster stack the predictions are only in good agreement at around the 1 - 2 Mpc scales, while for $r \gtrsim 10$ Mpc EG is in strong tension with the data. According to the Bayesian information criterion analysis, GR is preferred in all tested datasets; however, we also discuss possible modifications of EG that greatly relax the tension with the data.Comment: 19 pages, 5 figures, 5 tables, accepted for publication on JCA

Using machine learning to optimise chameleon fifth force experiments

The chameleon is a theorised scalar field that couples to matter and possess a screening mechanism, which weakens observational constraints from experiments performed in regions of higher matter density. One consequence of this screening mechanism is that the force induced by the field is dependent on the shape of the source mass (a property that distinguishes it from gravity). Therefore an optimal shape must exist for which the chameleon force is maximised. Such a shape would allow experiments to improve their sensitivity by simply changing the shape of the source mass. In this work we use a combination of genetic algorithms and the chameleon solving software SELCIE to find shapes that optimise the force at a single point in an idealised experimental environment. We note that the method we used is easily customised, and so could be used to optimise a more realistic experiment involving particle trajectories or the force acting on an extended body. We find the shapes outputted by the genetic algorithm possess common characteristics, such as a preference for smaller source masses, and that the largest fifth forces are produced by small `umbrella'-like shapes with a thickness such that the source is unscreened but the field reaches its minimum inside the source. This remains the optimal shape even as we change the chameleon potential, and the distance from the source, and across a wide range of chameleon parameters. We find that by optimising the shape in this way the fifth force can be increased by $2.45$ times when compared to a sphere, centred at the origin, of the same volume and mass.Comment: 28 pages, 17 figures, The SELCIE code is available at: https://github.com/C-Briddon/SELCI

SELCIE: a tool for investigating the chameleon field of arbitrary sources

The chameleon model is a modified gravity theory that introduces an additional scalar field that couples to matter through a conformal coupling. This `chameleon field' possesses a screening mechanism through a nonlinear self-interaction term which allows the field to affect cosmological observables in diffuse environments whilst still being consistent with current local experimental constraints. Due to the self-interaction term the equations of motion of the field are nonlinear and therefore difficult to solve analytically. The analytic solutions that do exist in the literature are either approximate solutions and or only apply to highly symmetric systems. In this work we introduce the software package SELCIE (https://github.com/C-Briddon/SELCIE.git). This package equips the user with tools to construct an arbitrary system of mass distributions and then to calculate the corresponding solution to the chameleon field equation. It accomplishes this by using the finite element method and either the Picard or Newton nonlinear solving methods. We compared the results produced by SELCIE with analytic results from the literature including discrete and continuous density distributions. We found strong (sub-percentage) agreement between the solutions calculated by SELCIE and the analytic solutions

Using machine learning to optimise chameleon fifth force experiments

The chameleon is a theorised scalar field that couples to matter and possess a screening mechanism, which weakens observational constraints from experiments performed in regions of higher matter density. One consequence of this screening mechanism is that the force induced by the field is dependent on the shape of the source mass (a property that distinguishes it from gravity). Therefore an optimal shape must exist for which the chameleon force is maximised. Such a shape would allow experiments to improve their sensitivity by simply changing the shape of the source mass. In this work we use a combination of genetic algorithms and the chameleon solving software SELCIE to find shapes that optimise the force at a single point in an idealised experimental environment. We note that the method we used is easily customised, and so could be used to optimise a more realistic experiment involving particle trajectories or the force acting on an extended body. We find the shapes outputted by the genetic algorithm possess common characteristics, such as a preference for smaller source masses, and that the largest fifth forces are produced by small `umbrella'-like shapes with a thickness such that the source is unscreened but the field reaches its minimum inside the source. This remains the optimal shape even as we change the chameleon potential, and the distance from the source, and across a wide range of chameleon parameters. We find that by optimising the shape in this way the fifth force can be increased by 2.45 times when compared to a sphere, centred at the origin, of the same volume and mass

Low-Dose Ketamine for Acute Postoperative Pain Treatment

Treatment of acute postoperative pain is an essential part of perioperative care and if left untreated could complicate the healing period. Ketamine blocks nociceptive pain and pain arising from inflammation. Therefore, it is potentially beneficial in the postoperative period. After systematic review using “MEDLINE/PubMed (NLM)” database, we analyzed 18 studies published during 2011–2020 and found that 0.5 mg/kg/h ketamine bolus and 0.1–0.25 mg/kg/h ketamine infusion to be the most effective dose to alleviate postoperative acute pain. Ketamine, when compared with a placebo, did not have any impact on patients’ satisfaction with postoperative pain management and overall well-being. Only three studies revealed more frequent adverse reactions to ketamine after surgery suggesting that ketamine did not have any impact on patients’ postoperational rehabilitation. So, it is the option to recommend low-dose ketamine to be part of multimodal analgesia in acute severe postoperative pain treatment. It can be used in both opioid-dependent and opioid-tolerant patients. Ketamine bolus should be ≤0.35 mg/kg and infusion ≤1 mg/kg/h. One should avoid the use of ketamine in pregnant women, people with cardiovascular diseases, acute psychosis, impaired liver function, increased intracranial, and intraocular pressure. Intranasal ketamine may be considered for children during procedures outside of the operation room

Managing selection of AFF power generation technologies in the internationally evolving carbon-free context

The article presents the analysis fossil fuel power generation market, focusing on management of advanced fossil fuel (AFF) power generation challenges of related technologies especially when tackling climate change impacts, complying with stricter environmental requirements. A wide and dynamic spectrum in scope and scale of factors revealed confirms the necessity for solutions enabling organizations to transform and manage rationally their fossil fuel-based business models towards greater competitiveness in the context of emerging renewable energy reliance. Nevertheless, in this respect the measures in question may require trade-offs, therefore when considering their combination, a diligent multicriteria analysis will inevitably be involved. With pivotal focus on the economic utility and the balanced and sustained strategic development of business, as the result of the research author proposes to apply VIKOR method when deciding on AFF power generation options. Application flexibility of the proposed method allow to evaluate, compare possible alternatives in a comprehensive and complex manner and to mingle MCDA tools if needed

Chameleon Screening Depends on the Shape and Structure of NFW Halos

Chameleon gravity is an example of a model that gives rise to interesting phenomenology on cosmological scales while simultaneously possessing a screening mechanism, allowing it to avoid solar system constraints. Such models result in non-linear field equations, which can be solved analytically only in simple highly symmetric systems. In this work we study the equation of motion of a scalar-tensor theory with chameleon screening using the finite element method. More specifically, we solve the field equation for spherical and triaxial NFW cluster-sized halos. This allows a detailed investigation of the relationship between the NFW concentration and the virial mass parameters and the magnitude of the chameleon acceleration, as measured at the virial radius. In addition, we investigate the effects on the chameleon acceleration due to halo triaxiality. We focus on the parameter space regions that are still allowed by the observational constraints. We find that given our dataset, the largest allowed value for the chameleon-to-NFW acceleration ratio at the virial radius is ∼10-7. This result strongly indicates that the chameleon models that are still allowed by the observational constraints would not lead to any measurable effects on galaxy cluster scales. Nonetheless, we also find that there is a direct relationship between the NFW potential and the chameleon-to-NFW acceleration ratio at the virial radius. Similarly, there is a direct (yet a much more complicated) relationship between the NFW concentration, the virial mass and the acceleration ratios at the virial radius. Finally, we find that triaxiality introduces extra directional effects on the acceleration measurements. These effects in combination could potentially be used in future observational searches for fifth forces

Chameleon Screening in Cosmic Voids

A key goal in cosmology in the upcoming decade will be to form a better understanding of the accelerated expansion of the Universe. Upcoming surveys, such as the Vera C. Rubin Observatory's 10-year Legacy Survey of Space and Time (LSST), Euclid and the Square Killometer Array (SKA) will deliver key datasets required to tackle this and other puzzles in contemporary cosmology. With this data, constraints of unprecedented power will be put on different models of dark energy and modified gravity. In this context it is crucial to understand how screening mechanisms, which hide the deviations of these theories from the predictions of general relativity in local experiments, affect structure formation. In this work we approach this problem by using a combination of analytic and numerical methods to describe chameleon screening in the context of cosmic voids. We apply a finite element method code, SELCIE, to solve the chameleon equation of motion for a number of void profiles derived from observational data and simulations. The obtained results indicate a complex relationship between the properties of cosmic voids and the size of the chameleon acceleration of a test particle. We find that the fifth force on a test particle in a void is primarily related to the depth and the inner density gradient of the void. For realistic void profiles, the obtained chameleon-to-Newtonian acceleration ratios range between $a_{\phi}/a_{\rm Newt} \approx 10^{-6} - 10^{-5}$. However, it should be noted that in unusually deep voids with large inner density gradients, the acceleration ratios can be significantly higher. We also discuss the optimal density profiles for detecting the fifth force in the upcoming observational surveys.Comment: 16 pages, 8 figures. The SELCIE code is available at: https://github.com/C-Briddon/SELCIE. Submitted to JCA