Optimization Research on Geometric Parameters of Scallop-Shaped Lattice Shells

Li, Na; Chang, Ren An; Zong, Wei Qi; Yu, Qi Hang

doi:10.4028/www.scientific.net/amm.724.192

Cited by 4 publications

(8 citation statements)

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“…IV E 4. The latter models, dubbed non-minimal entropic, are based on replacing the tachyonic isocurvature field during the ekpyrotic phase, which we focus on in the following, by a non-minimally coupled entropic field as first proposed in [169,170]. These models still encompass non-Gaussianity from the conversion mechanism.…”

Section: E Non-gaussianitiesmentioning

confidence: 99%

“…This work superseded that of [170] which set up the building blocks to obtain scale-invariant entropy perturbations within the ekpyrotic scenario via non-minimally coupled massless scalar fields. There, it was suggested that the entropy perturbation could be converted into curvature perturbations by means of a curvaton, as done in [169], or modulated (p)reheating [245].…”

Section: F Nonsingular Bounces Via a Galileonmentioning

confidence: 99%

“…However, after the publication of PLANCK, the emphasis was put onto the possibility to counterbalance different contributions to non-Gaussianities to enable f local NL of order 1 [152]. To this end, the focus shifted to potentials approximately symmetric transverse to the adiabatic direction, as well as non-minimal entropic models [169][170][171][172]. All these models entail an unobservable primordial gravitational wave spectrum; they are therefore ruled out if the BICEP2 detection of r ∼ 0.2 is confirmed to be a signal of primordial origin by the future Keck Array observations at 100 GHZ and PLANCK observations at higher frequency [33,34], see Sec.…”

Section: B Ekpyrotic and Cyclic Scenariosmentioning

confidence: 99%

“…via a galileon/ghost condensate, as in the matter bounce scenario [225], the super-bounce [71] or the non-minimal entropic bounce [169,170], 2. via a thermal string gas in the S-brane bounce [202] or the Hagedorn phase in string gas cosmology [388].…”

Section: A Preheating and Reheatingmentioning

confidence: 99%

“…A model which does not generate large intrinsic nonGaussianities is that based on a non-minimal entropic mechanism [171,172], following the model introduced in [169,170]. It employs a second scalar, which does not contribute to the potential, but is non-minimally coupled to the ekpyrotic scalar φ in its kinetic function.…”

Section: Non-gaussianities In Other Proposalsmentioning

confidence: 99%

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A critical review of classical bouncing cosmologies

2015

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Given the proliferation of bouncing models in recent years, we gather and critically assess these proposals in a comprehensive review. The PLANCK data shows an unmistakably red, quasi scaleinvariant, purely adiabatic primordial power spectrum and no primary non-Gaussianities. While these observations are consistent with inflationary predictions, bouncing cosmologies aspire to provide an alternative framework to explain them. Such models face many problems, both of the purely theoretical kind, such as the necessity of violating the NEC and instabilities, and at the cosmological application level, as exemplified by the possible presence of shear. We provide a pedagogical introduction to these problems and also assess the fitness of different proposals with respect to the data. For example, many models predict a slightly blue spectrum and must be fine-tuned to generate a red spectral index; as a side effect, large non-Gaussianities often result.We highlight several promising attempts to violate the NEC without introducing dangerous instabilities at the classical and/or quantum level. If primordial gravitational waves are observed, certain bouncing cosmologies, such as the cyclic scenario, are in trouble, while others remain valid. We conclude that, while most bouncing cosmologies are far from providing an alternative to the inflationary paradigm, a handful of interesting proposals have surfaced, which warrant further research. The constraints and lessons learned as laid out in this review might guide future research.

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Section: E Non-gaussianitiesmentioning

confidence: 99%

Section: F Nonsingular Bounces Via a Galileonmentioning

confidence: 99%

Section: B Ekpyrotic and Cyclic Scenariosmentioning

confidence: 99%

Section: A Preheating and Reheatingmentioning

confidence: 99%

Section: Non-gaussianities In Other Proposalsmentioning

confidence: 99%

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A critical review of classical bouncing cosmologies

2015

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Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies

Ijjas

Steinhardt

2016

Class. Quantum Grav.

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The results from Planck2015, when combined with earlier observations from WMAP, ACT, SPT and other experiments, were the first observations to disfavor the "classic" inflationary paradigm. To satisfy the observational constraints, inflationary theorists have been forced to consider plateau-like inflaton potentials that introduce more parameters and more fine-tuning, problematic initial conditions, multiverse-unpredictability issues, and a new 'unlikeliness problem.' Some propose turning instead to a "postmodern" inflationary paradigm in which the cosmological properties in our observable universe are only locally valid and set randomly, with completely different properties (and perhaps even different physical laws) existing in most regions outside our horizon. By contrast, the new results are consistent with the simplest versions of ekpyrotic cyclic models in which the universe is smoothed and flattened during a period of slow contraction followed by a bounce, and another promising bouncing theory, anamorphic cosmology, has been proposed that can produce distinctive predictions.The Planck2015 [1] and Planck2013 [2] observations, combined with the results by the Wilkinson Microwave Anisotropy Probe (WMAP), Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT) teams have shown that the measured spatial curvature is small; the spectrum of primordial density fluctuations is nearly scale-invariant; there is a small spectral tilt, consistent with a simple dynamical mechanism that caused the smoothing and flattening; and the fluctuations are nearly gaussian. These features are all consistent with the simplest textbook inflationary models. At the same time, Planck2015 also confirmed that r, the ratio of the tensor perturbation amplitude to the scalar perturbation amplitude, is less than 0.1, a result that virtually eliminates all the simplest textbook inflationary models. The development is notable because, as emphasized by Ijjas et al. [3], it is the first time that the classic inflationary picture has been in conflict with observations.The results have led theorists to consider alternative plateau-like inflationary models whose parameters can be adjusted to reduce the expected value of r while retaining all the rest of the classic predictions. However, as we explain in this brief review, the remaining models raise new issues. They require more parameters, more tuning of parameters, more tuning of initial conditions, a worsened multiverse-unpredictability problem, and a new challenge that we call the inflationary 'unlikeliness problem. ' One response to these problems has been that they should be ignored. The classic inflationary picture should be abandoned in favor of an alternative 'postmodern' inflationary picture that allows enough flexibility to fit any combination of observations. The classic and postmodern inflationary pictures are so different that they ought to be viewed as distinct paradigms to be judged separately.A more promising response to Planck2015 has been to develop "bouncing" cosmologie...

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Optimization Research on Geometric Parameters of Scallop-Shaped Lattice Shells

Cited by 4 publications

References 5 publications

A critical review of classical bouncing cosmologies

A critical review of classical bouncing cosmologies

Mechanical performance of sinusoidally architected concrete enabled by robotic additive manufacturing

Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies

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