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A Marcoscaballero - One of the best experts on this subject based on the ideXlab platform.
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primordial black hole formation with non Gaussian Curvature perturbations
Journal of Cosmology and Astroparticle Physics, 2019Co-Authors: Vicente Atal, Jaume Garriga, A MarcoscaballeroAbstract:In the context of transient constant-roll inflation near a local maximum, we derive the non-perturbative field redefinition that relates a Gaussian random field with the true non-Gaussian Curvature perturbation. Our analysis shows the emergence of a new critical amplitude ζ*, corresponding to perturbations that prevent the inflaton from overshooting the local maximum, thus becoming trapped in the false minimum of the potential. For potentials with a mild Curvature at the local maximum (and thus small non-Gaussianity), we recover the known perturbative field redefinition. We apply these results to the formation of primordial black holes, and discuss the cases for which ζ* is smaller or of the same order than the critical value for collapse of spherically symmetric overdensities. In the latter case, we present a simple potential for which the power spectrum needs an amplitude 10 times smaller that in the Gaussian case for producing a sizeable amount of primordial black holes.
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primordial black hole formation with non Gaussian Curvature perturbations
arXiv: Cosmology and Nongalactic Astrophysics, 2019Co-Authors: Vicente Atal, Jaume Garriga, A MarcoscaballeroAbstract:In the context of transient constant-roll inflation near a local maximum, we derive the non-perturbative field redefinition that relates a Gaussian random field with the true non-Gaussian Curvature perturbation. Our analysis shows the emergence of a new critical amplitude $\zeta_*$, corresponding to perturbations that prevent the inflaton from overshooting the local maximum, thus becoming trapped in the false minimum of the potential. For potentials with a mild Curvature at the local maximum (and thus small non-Gaussianity), we recover the known perturbative field redefinition. We apply these results to the formation of primordial black holes, and discuss the cases for which $\zeta_*$ is smaller or of the same order than the critical value for collapse of spherically symmetric overdensities. In the latter case, we present a simple potential for which the power spectrum needs an amplitude 10 times smaller that in the Gaussian case for producing a sizeable amount of primordial black holes.
Qingguo Huang - One of the best experts on this subject based on the ideXlab platform.
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gravitational waves induced by the local type non Gaussian Curvature perturbations
Physics Letters B, 2021Co-Authors: Chen Yuan, Qingguo HuangAbstract:Abstract The current observational constraints still leave a substantial mass window ∼ [ 10 − 16 , 10 − 14 ] ∪ [ 10 − 13 , 10 − 12 ] M ⊙ for primordial black holes (PBHs) representing all of dark matter (DM) in our Universe. The gravitational waves (GWs) induced by the Curvature perturbations are inevitably generated during the formation of these PBHs, and fall in the frequency band of LISA. Such scalar induced gravitational waves (SIGWs) are supposed to be definitely detected by LISA even when the second-order local-type non-Gaussianity characterized by the parameter F NL is taken into account. In this letter, we give a comprehensive analysis of the GWs induced by the local-type non-Gaussian Curvature perturbations up to the third-order denoted by the non-linear parameter G NL , and we find that a log-dependent slope of SIGWs in the infrared region is generically predicted and the amplitude of SIGWs can be further suppressed by several orders of magnitude. As a result, the null-detection of SIGWs by LISA cannot rule out the possibility of PBHs making up all of DM.
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gravitational waves induced by the local type non Gaussian Curvature perturbations
arXiv: Cosmology and Nongalactic Astrophysics, 2020Co-Authors: Chen Yuan, Qingguo HuangAbstract:The current observational constraints still leave a substantial mass window $\sim [10^{-16},10^{-14}] \cup [10^{-13},10^{-12}] M_\odot$ for primordial black holes (PBHs) representing all of dark matter (DM) in our Universe. The gravitational waves (GWs) induced by the Curvature perturbations are inevitably generated during the formation of these PBHs, and fall in the frequency band of LISA. Such scalar induced gravitational waves (SIGWs) are supposed to be definitely detected by LISA even when the second-order local-type non-Gaussianity characterized by the parameter $F_{\rm NL}$ is taken into account. In this letter, we give a comprehensive analysis of the GWs induced by the local-type non-Gaussian Curvature perturbations up to the third-order denoted by the non-linear parameter $G_{\rm NL}$, and find that a log-dependent slope of SIGWs in the infrared region is generically predicted and the amplitude of SIGWs can be further suppressed by several orders of magnitude. Therefore, the null-detection of SIGWs by LISA cannot rule out the possibility of PBHs making up all of DM.
Markus Deserno - One of the best experts on this subject based on the ideXlab platform.
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Gaussian Curvature elasticity determined from global shape transformations and local stress distributions a comparative study using the martini model
Faraday Discussions, 2013Co-Authors: Djurre H De Jong, Siewert J Marrink, Markus DesernoAbstract:We calculate the Gaussian Curvature modulus of a systematically coarse-grained (CG) one-component lipid membrane by applying the method recently proposed by Hu et al. [Biophys. J., 2012, 102, 1403] to the MARTINI representation of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). We find the value /κ = −1.04 ± 0.03 for the elastic ratio between the Gaussian and the mean Curvature modulus and deduce m/κm ≈ −0.98 ± 0.09 for the monolayer elastic ratio, where the latter is based on plausible assumptions for the distance z0 of the monolayer neutral surface from the bilayer midplane and the spontaneous lipid Curvature K0m. By also analyzing the lateral stress profile σ0(z) of our system, two other lipid types and pertinent data from the literature, we show that determining K0m and through the first and second moment of σ0(z) gives rise to physically implausible values for these observables. This discrepancy, which we previously observed for a much simpler CG model, suggests that the moment conditions derived from simple continuum assumptions miss the effect of physically important correlations in the lipid bilayer.
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determining the Gaussian Curvature modulus of lipid membranes in simulations
Biophysical Journal, 2012Co-Authors: John J Briguglio, Markus DesernoAbstract:The Gaussian Curvature modulus κ¯ of lipid bilayers likely contributes more than 100 kcal/mol to every cellular fission or fusion event. This huge impact on membrane remodeling energetics might be a factor that codetermines the complex lipid composition of biomembranes through tuning of κ¯. Yet, its value has been measured only for a handful of simple lipids, and no simulation has so far determined it better than a factor of two, rendering a systematic investigation of such enticing speculations impossible. Here we propose a highly accurate method to determine κ¯ in computer simulations. It relies on the interplay between Curvature stress and edge tension of partially curved axisymmetric membrane disks and requires determining their closing probability. For a simplified lipid model we obtain κ¯ and its relation to the normal bending modulus κ for membranes differing both in stiffness and spontaneous lipid Curvature. The elastic ratio κ¯/κ can be determined with a few percent statistical accuracy. Its value agrees with the scarce experimental data, and its change with spontaneous lipid Curvature is compatible with theoretical expectations, thereby granting additional information on monolayer properties. We also show that an alternative determination of these elastic parameters based on moments of the lateral stress profile gives markedly different and unphysical values.
Timothy J. White - One of the best experts on this subject based on the ideXlab platform.
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Encoding Gaussian Curvature in glassy and elastomeric liquid crystal solids
Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2016Co-Authors: Cyrus Mostajeran, Mark Warner, Taylor H. Ware, Timothy J. WhiteAbstract:We describe shape transitions of thin, solid nematic sheets with smooth, preprogrammed, in-plane director fields patterned across the surface causing spatially inhomogeneous local deformations. A metric description of the local deformations is used to study the intrinsic geometry of the resulting surfaces upon exposure to stimuli such as light and heat. We highlight specific patterns that encode constant Gaussian Curvature of prescribed sign and magnitude. We present the first experimental results for such programmed solids, and they qualitatively support theory for both positive and negative Gaussian Curvature morphing from flat sheets on stimulation by light or heat. We review logarithmic spiral patterns that generate cone/anti-cone surfaces, and introduce spiral director fields that encode non-localized positive and negative Gaussian Curvature on punctured discs, including spherical caps and spherical spindles. Conditions are derived where these cap-like, photomechanically responsive regions can be anchored in inert substrates by designing solutions that ensure compatibility with the geometric constraints imposed by the surrounding media. This integration of such materials is a precondition for their exploitation in new devices. Finally, we consider the radial extension of such director fields to larger sheets using nematic textures defined on annular domains.
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encoding Gaussian Curvature in glassy and elastomeric liquid crystal polymer networks
arXiv: Soft Condensed Matter, 2015Co-Authors: Cyrus Mostajeran, Taylor H. Ware, Timothy J. WhiteAbstract:Considerable recent attention has been given to the study of shape formation using modern responsive materials that can be preprogrammed to undergo spatially inhomogeneous local deformations. In particular, nematic liquid crystal polymer networks offer exciting possibilities in this context. In this paper, we discuss the generation of Gaussian Curvature in thin nematic sheets using smooth in-plane director fields patterned across the surface. We highlight specific patterns which encode constant Gaussian Curvature of prescribed sign and magnitude and present experimental results which appear to support the theoretical predictions. Specifically, we provide experimental evidence for the realization of positive and negative Gaussian Curvature in glassy and elastomeric liquid crystal polymer networks through the stimulation of smoothly varying in-plane director fields.
Vicente Atal - One of the best experts on this subject based on the ideXlab platform.
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primordial black hole formation with non Gaussian Curvature perturbations
Journal of Cosmology and Astroparticle Physics, 2019Co-Authors: Vicente Atal, Jaume Garriga, A MarcoscaballeroAbstract:In the context of transient constant-roll inflation near a local maximum, we derive the non-perturbative field redefinition that relates a Gaussian random field with the true non-Gaussian Curvature perturbation. Our analysis shows the emergence of a new critical amplitude ζ*, corresponding to perturbations that prevent the inflaton from overshooting the local maximum, thus becoming trapped in the false minimum of the potential. For potentials with a mild Curvature at the local maximum (and thus small non-Gaussianity), we recover the known perturbative field redefinition. We apply these results to the formation of primordial black holes, and discuss the cases for which ζ* is smaller or of the same order than the critical value for collapse of spherically symmetric overdensities. In the latter case, we present a simple potential for which the power spectrum needs an amplitude 10 times smaller that in the Gaussian case for producing a sizeable amount of primordial black holes.
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primordial black hole formation with non Gaussian Curvature perturbations
arXiv: Cosmology and Nongalactic Astrophysics, 2019Co-Authors: Vicente Atal, Jaume Garriga, A MarcoscaballeroAbstract:In the context of transient constant-roll inflation near a local maximum, we derive the non-perturbative field redefinition that relates a Gaussian random field with the true non-Gaussian Curvature perturbation. Our analysis shows the emergence of a new critical amplitude $\zeta_*$, corresponding to perturbations that prevent the inflaton from overshooting the local maximum, thus becoming trapped in the false minimum of the potential. For potentials with a mild Curvature at the local maximum (and thus small non-Gaussianity), we recover the known perturbative field redefinition. We apply these results to the formation of primordial black holes, and discuss the cases for which $\zeta_*$ is smaller or of the same order than the critical value for collapse of spherically symmetric overdensities. In the latter case, we present a simple potential for which the power spectrum needs an amplitude 10 times smaller that in the Gaussian case for producing a sizeable amount of primordial black holes.