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Misao Sasaki - One of the best experts on this subject based on the ideXlab platform.
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revisiting non gaussianity from non attractor inflation models
Journal of Cosmology and Astroparticle Physics, 2018Co-Authors: Yifu Cai, Mohammad Hossein Namjoo, Misao Sasaki, Xingang Chen, Donggang Wang, Ziwei WangAbstract:Non-attractor inflation is known as the only single field inflationary scenario that can violate Non-Gaussianity consistency relation with the Bunch-Davies vacuum state and generate large local Non-Gaussianity. However, it is also known that the non-attractor inflation by itself is incomplete and should be followed by a phase of slow-roll attractor. Moreover, there is a transition process between these two phases. In the past literature, this transition was approximated as instant and the evolution of Non-Gaussianity in this phase was not fully studied. In this paper, we follow the detailed evolution of the Non-Gaussianity through the transition phase into the slow-roll attractor phase, considering different types of transition. We find that the transition process has important effect on the size of the local Non-Gaussianity. We first compute the net contribution of the non-Gaussianities at the end of inflation in canonical non-attractor models. If the curvature perturbations keep evolving during the transition—such as in the case of smooth transition or some sharp transition scenarios—the (1) local Non-Gaussianity generated in the non-attractor phase can be completely erased by the subsequent evolution, although the consistency relation remains violated. In extremal cases of sharp transition where the super-horizon modes freeze immediately right after the end of the non-attractor phase, the original non-attractor result can be recovered. We also study models with non-canonical kinetic terms, and find that the transition can typically contribute a suppression factor in the squeezed bispectrum, but the final local Non-Gaussianity can still be made parametrically large.
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global adiabaticity and non gaussianity consistency condition
Physics Letters B, 2016Co-Authors: Sander Mooij, Antonio Enea Romano, Misao SasakiAbstract:Abstract In the context of single-field inflation, the conservation of the curvature perturbation on comoving slices, R c , on super-horizon scales is one of the assumptions necessary to derive the consistency condition between the squeezed limit of the bispectrum and the spectrum of the primordial curvature perturbation. However, the conservation of R c holds only after the perturbation has reached the adiabatic limit where the constant mode of R c dominates over the other (usually decaying) mode. In this case, the non-adiabatic pressure perturbation defined in the thermodynamic sense, δ P n a d ≡ δ P − c w 2 δ ρ where c w 2 = P ˙ / ρ ˙ , usually becomes also negligible on superhorizon scales. Therefore one might think that the adiabatic limit is the same as thermodynamic adiabaticity. This is in fact not true. In other words, thermodynamic adiabaticity is not a sufficient condition for the conservation of R c on super-horizon scales. In this paper, we consider models that satisfy δ P n a d = 0 on all scales, which we call global adiabaticity (GA), which is guaranteed if c w 2 = c s 2 , where c s is the phase velocity of the propagation of the perturbation. A known example is the case of ultra-slow-roll (USR) inflation in which c w 2 = c s 2 = 1 . In order to generalize USR we develop a method to find the Lagrangian of GA K-inflation models from the behavior of background quantities as functions of the scale factor. Applying this method we show that there indeed exists a wide class of GA models with c w 2 = c s 2 , which allows R c to grow on superhorizon scales, and hence violates the Non-Gaussianity consistency condition.
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violation of non gaussianity consistency relation in a single field inflationary model
EPL, 2013Co-Authors: Mohammad Hossein Namjoo, Hassan Firouzjahi, Misao SasakiAbstract:In this paper we present a simple, toy model of single-field inflation in which the standard Non-Gaussianity consistency condition is violated. In this model the curvature perturbations on super-horizon scales are not conserved and the decaying modes of perturbations are not negligible in the non-attractor phase. As a result a large local Non-Gaussianity can be obtained in the squeezed limit which violates the standard Non-Gaussianity consistency condition for the single-field models.
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large non gaussianity from multi brid inflation
International Journal of Modern Physics: Conference Series, 2011Co-Authors: Atsushi Naruko, Misao SasakiAbstract:A model of multi-component hybrid inflation, dubbed multi-brid inflation, which may yield a large non-Gaussian paramter fNL, was proposed recently. In particular, for a two-brid inflation model with an exponential potential and the condition that the end of inflation is an ellipse in the field space, it was found that, while keeping the other observational quantities within the range consistent with observations, large Non-Gaussianity is possible for certain inflationary trajectories. In this talk, in order to see if this result is a general feature of multi-brid inflation, we consider a model with a potential with an exponent quadratic in the scalar field components. We also consider a more general class of ellipses for the end of inflation. Focusing on the case of two-brid inflation, we find that large Non-Gaussianity is also possible in the present model. Then by tuning the model parameters, we find that there exist models for which both the Non-Gaussianity and the tensor-to-scalar ratio are large enough to be detected in the very near future.
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large non gaussianity from multi brid inflation
Progress of Theoretical Physics, 2009Co-Authors: Atsushi Naruko, Misao SasakiAbstract:A model of multi-component hybrid inflation, dubbed multi-brid inflation, in which various observable quantities including the Non-Gaussianity parameter fNL can be analytically calculated was proposed recently. In particular, for a two-brid inflation model with an exponential potential and the condition that the end of inflation is an ellipse in the field space, it was found that, while keeping the other observational quantities within the range consistent with observations, large Non-Gaussianity is possible for certain inflationary trajectories, provided that the ratio of the two masses is large. One might question whether the resulting large Non-Gaussianity is specific to this particular form of the potential and the condition for the end of inflation. In this paper, we consider a model of multi-brid inflation with a potential given by an exponential function of terms quadratic in the scalar field components. We also consider a more general class of ellipses for the end of inflation than those studied previously. Then, focusing on the case of two-brid inflation, we find that large Non-Gaussianity is possible in the present model even for the equal-mass case. Then by tuning the model parameters, we find that there exist models for which both the Non-Gaussianity and the tensor-to-scalar ratio are large enough to be detected in the very near future. Subject Index: 440
Stefano Camera - One of the best experts on this subject based on the ideXlab platform.
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probing primordial non gaussianity with ska galaxy redshift surveys a fully relativistic analysis
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: Roy Maartens, Stefano Camera, Mario G SantosAbstract:The Square Kilometre Array (SKA) will produce spectroscopic surveys of tens to hundreds of millions of neutral hydrogen (H I) galaxies, eventually covering 30 000 deg2 and reaching out to redshift z≳2. The huge volumes probed by the SKA will allow for some of the best constraints on primordial Non-Gaussianity, based on measurements of the large-scale power spectrum.We investigate various observational set-ups for HI galaxy redshift surveys, compatible with the SKA Phase 1 and Phase 2 (full SKA) configurations.We use the corresponding number counts and bias for each survey from realistic simulations and derive the magnification bias and the evolution of source counts directly from these. For the first time, we produce forecasts that fully include the general relativistic effects on the galaxy number counts. These corrections to the standard analysis become important on very large scales, where the signal of primordial Non-Gaussianity grows strongest. Our results showthat, for the full survey, the Non-Gaussianity parameter fNL can be constrained down to σ(fNL) = 1.54. This improves the current limit set by the Planck satellite by a factor of 5, using a completely different approach.
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probing primordial non gaussianity via isw measurements with ska continuum surveys
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: O Dore, Roy Maartens, Alvise Raccanelli, Mario G Santos, D J Bacon, Stefano CameraAbstract:The Planck CMB experiment has delivered the best constraints so far on primordial Non-Gaussianity, ruling out early-Universe models of inflation that generate large Non-Gaussianity. Although small improvements in the CMB constraints are expected, the next frontier of precision will come from future large-scale surveys of the galaxy distribution. The advantage of such surveys is that they can measure many more modes than the CMB -- in particular, forthcoming radio surveys with the SKA will cover huge volumes. Radio continuum surveys deliver the largest volumes, but with the disadvantage of no redshift information. In order to mitigate this, we use two additional observables. First, the integrated Sachs-Wolfe effect -- the cross-correlation of the radio number counts with the CMB temperature anisotropies -- helps to reduce systematics on the large scales that are sensitive to Non-Gaussianity. Second, optical data allows for cross-identification in order to gain some redshift information. We show that, while the single redshift bin case can provide a sigma(fNL) ~ 20, and is therefore not competitive with current and future constraints on Non-Gaussianity, a tomographic analysis could improve the constraints by an order of magnitude, even with only two redshift bins. A huge improvement is provided by the addition of high-redshift sources, so having cross-ID for high-z galaxies and an even higher-z radio tail is key to enabling very precise measurements of fNL. Our results show that SKA continuum surveys could provide constraints competitive with CMB and forthcoming optical surveys, potentially allowing a measurement of sigma(fNL) ~ 1 to be made. Moreover, these measurements would act as a useful check of results obtained with other probes at other redshift ranges with other methods.
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cosmology on ultralarge scales with intensity mapping of the neutral hydrogen 21 cm emission limits on primordial non gaussianity
Physical Review Letters, 2013Co-Authors: Stefano Camera, Mario G Santos, Pedro G Ferreira, Luis FerramachoAbstract:: The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts z=/~1-5 are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial Non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the Non-Gaussianity parameter f(NL), with an error close to σ(f(NL))~1.
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cosmology on ultralarge scales with intensity mapping of the neutral hydrogen 21 cm emission limits on primordial non gaussianity
Physical Review Letters, 2013Co-Authors: Stefano Camera, Mario G Santos, Pedro G Ferreira, Luis FerramachoAbstract:The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts $z\ensuremath{\simeq}1--5$ are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial Non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the Non-Gaussianity parameter ${f}_{\mathrm{NL}}$, with an error close to ${\ensuremath{\sigma}}_{{f}_{\mathrm{NL}}}\ensuremath{\sim}1$.
L Cayon - One of the best experts on this subject based on the ideXlab platform.
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probability of the most massive cluster under non gaussian initial conditions
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: L Cayon, Christopher Gordon, Joseph SilkAbstract:Very massive high redshift clusters can be used to constrain and test theCDM model. Taking into account the observational constraints of Jee et al. (2009) we have calculated the probability for the most massive cluster to be found in the range (5.2− 7.6)×10 14 M⊙, between redshifts 1.4 6 z 6 2.2, with a sky area of 11 deg 2 and under non-Gaussian initial conditions. Clusters constrain the Non-Gaussianity on smaller scales than current cosmic microwave background or halo bias data and so can be used to test for running of the Non-Gaussianity parameter fNL.
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probability of the most massive cluster under non gaussian initial conditions
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: L Cayon, Christopher Gordon, Joseph SilkAbstract:Very massive high redshift clusters can be used to constrain and test the Lambda CDM model. Taking into account the observational constraints of Jee et al. (2009) we have calculated the probability for the most massive cluster to be found in the range (5.2-7.6)e14 M_sun, between redshifts 1.4-2.2, with a sky area of 11 sqdeg and under non-Gaussian initial conditions. Clusters constrain the Non-Gaussianity on smaller scales than current cosmic microwave background or halo bias data and so can be used to test for running of the Non-Gaussianity parameter f_NL.
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detection of non gaussianity in the wilkinson microwave anisotropy probe first year data using spherical wavelets
The Astrophysical Journal, 2004Co-Authors: P Vielva, J. L. Sanz, R B Barreiro, E Martinezgonzalez, L CayonAbstract:A non-Gaussian detection in the Wilkinson Microwave Anisotropy Probe (WMAP) first-year data is reported. The detection has been found in the combined Q - V - W map proposed by the WMAP team after applying a wavelet technique based on the spherical Mexican hat wavelet (SMHW). The skewness and the kurtosis of the SMHW coefficients are calculated at different scales (ranging from a few arcminutes to tens of degrees). A non-Gaussian signal is detected at scales of the SMHW around 4° (size in the sky of around 10°). The right-tail probability of the detection is ≈0.4%. In addition, a study of Gaussianity is performed in each hemisphere. The northern hemisphere is compatible with Gaussianity, whereas the southern one deviates from Gaussianity with a right-tail probability of ≈0.1%. Systematics, foregrounds, and uncertainties in the estimation of the cosmological parameters are carefully studied in order to identify the possible source of Non-Gaussianity. The detected deviation from Gaussianity is not found to be caused by systematic effects: (1) Each one of the Q, V, and W receivers shows the same Non-Gaussianity pattern. (2) Several combinations of the different receivers at each frequency band—which highly reduce the cosmic microwave background (CMB) and the foreground emissions—do not show this non-Gaussian pattern. Similarly, Galactic foregrounds show a negligible contribution to the non-Gaussian detection: Non-Gaussianity is detected in all the WMAP maps (from 23 to 94 GHz), and no frequency dependence is observed. Moreover, the expected foreground contribution to the combined WMAP map was added to CMB Gaussian simulations showing a behavior compatible with the Gaussian model. The influence of uncertainties in the CMB power spectrum estimation are also quantified. Hence, possible intrinsic temperature fluctuations (such as secondary anisotropies and primordial features) cannot be rejected as the source of this non-Gaussian detection. We remark that our result implies not only asymmetries north/south—like other previous WMAP analyses—but also a direct non-Gaussian detection.
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detection of non gaussianity in the wmap 1 year data using spherical wavelets
arXiv: Astrophysics, 2003Co-Authors: P Vielva, J. L. Sanz, R B Barreiro, E Martinezgonzalez, L CayonAbstract:A non-Gaussian detection in the WMAP 1-year data is reported. The detection has been found in the combined Q-V-W map proposed by the WMAP team (Komatsu et al. 2003) after applying a wavelet technique based on the Spherical Mexican Hat Wavelet (SMHW). The skewness and the kurtosis of the SMHW coefficients are calculated at different scales. A non-Gaussian signal is detected at scales of the SMHW around 4 deg (size in the sky of around 10 deg). The right tail probability of the detection is approx. 0.4%. In addition, a study of Gaussianity is performed in each hemisphere. The northern hemisphere is compatible with Gaussianity, whereas the southern one deviates from Gaussianity with a right tail probability of approx. 0.1%. Systematics, foregrounds and uncertainties in the estimation of the cosmological parameters are carefully studied in order to identify the possible source of Non-Gaussianity. The detected deviation from Gaussianity is not found to be caused by systematic effects: 1) each one of the Q, V and W receivers shows the same Non-Gaussianity pattern, and 2) several combinations of the different receivers at each frequency band do not show this non-Gaussian pattern. Similarly, galactic foregrounds show a negligible contribution to the non-Gaussian detection: Non-Gaussianity is detected in all the WMAP maps and no frequency dependence is observed. Moreover, the expected foreground contribution to the combined WMAP map was added to CMB Gaussian simulations showing a behaviour compatible with the Gaussian model. Influence of uncertainties in the CMB power spectrum estimation are also quantified. Hence, possible intrinsic temperature fluctuations (like secondary anisotropies and primordial features) can not be rejected as the source of this non-Gaussian detection.
Luis Ferramacho - One of the best experts on this subject based on the ideXlab platform.
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cosmology on ultralarge scales with intensity mapping of the neutral hydrogen 21 cm emission limits on primordial non gaussianity
Physical Review Letters, 2013Co-Authors: Stefano Camera, Mario G Santos, Pedro G Ferreira, Luis FerramachoAbstract:: The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts z=/~1-5 are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial Non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the Non-Gaussianity parameter f(NL), with an error close to σ(f(NL))~1.
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cosmology on ultralarge scales with intensity mapping of the neutral hydrogen 21 cm emission limits on primordial non gaussianity
Physical Review Letters, 2013Co-Authors: Stefano Camera, Mario G Santos, Pedro G Ferreira, Luis FerramachoAbstract:The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts $z\ensuremath{\simeq}1--5$ are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial Non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the Non-Gaussianity parameter ${f}_{\mathrm{NL}}$, with an error close to ${\ensuremath{\sigma}}_{{f}_{\mathrm{NL}}}\ensuremath{\sim}1$.
Mario G Santos - One of the best experts on this subject based on the ideXlab platform.
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probing primordial non gaussianity with ska galaxy redshift surveys a fully relativistic analysis
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: Roy Maartens, Stefano Camera, Mario G SantosAbstract:The Square Kilometre Array (SKA) will produce spectroscopic surveys of tens to hundreds of millions of neutral hydrogen (H I) galaxies, eventually covering 30 000 deg2 and reaching out to redshift z≳2. The huge volumes probed by the SKA will allow for some of the best constraints on primordial Non-Gaussianity, based on measurements of the large-scale power spectrum.We investigate various observational set-ups for HI galaxy redshift surveys, compatible with the SKA Phase 1 and Phase 2 (full SKA) configurations.We use the corresponding number counts and bias for each survey from realistic simulations and derive the magnification bias and the evolution of source counts directly from these. For the first time, we produce forecasts that fully include the general relativistic effects on the galaxy number counts. These corrections to the standard analysis become important on very large scales, where the signal of primordial Non-Gaussianity grows strongest. Our results showthat, for the full survey, the Non-Gaussianity parameter fNL can be constrained down to σ(fNL) = 1.54. This improves the current limit set by the Planck satellite by a factor of 5, using a completely different approach.
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probing primordial non gaussianity via isw measurements with ska continuum surveys
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: O Dore, Roy Maartens, Alvise Raccanelli, Mario G Santos, D J Bacon, Stefano CameraAbstract:The Planck CMB experiment has delivered the best constraints so far on primordial Non-Gaussianity, ruling out early-Universe models of inflation that generate large Non-Gaussianity. Although small improvements in the CMB constraints are expected, the next frontier of precision will come from future large-scale surveys of the galaxy distribution. The advantage of such surveys is that they can measure many more modes than the CMB -- in particular, forthcoming radio surveys with the SKA will cover huge volumes. Radio continuum surveys deliver the largest volumes, but with the disadvantage of no redshift information. In order to mitigate this, we use two additional observables. First, the integrated Sachs-Wolfe effect -- the cross-correlation of the radio number counts with the CMB temperature anisotropies -- helps to reduce systematics on the large scales that are sensitive to Non-Gaussianity. Second, optical data allows for cross-identification in order to gain some redshift information. We show that, while the single redshift bin case can provide a sigma(fNL) ~ 20, and is therefore not competitive with current and future constraints on Non-Gaussianity, a tomographic analysis could improve the constraints by an order of magnitude, even with only two redshift bins. A huge improvement is provided by the addition of high-redshift sources, so having cross-ID for high-z galaxies and an even higher-z radio tail is key to enabling very precise measurements of fNL. Our results show that SKA continuum surveys could provide constraints competitive with CMB and forthcoming optical surveys, potentially allowing a measurement of sigma(fNL) ~ 1 to be made. Moreover, these measurements would act as a useful check of results obtained with other probes at other redshift ranges with other methods.
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cosmology on ultralarge scales with intensity mapping of the neutral hydrogen 21 cm emission limits on primordial non gaussianity
Physical Review Letters, 2013Co-Authors: Stefano Camera, Mario G Santos, Pedro G Ferreira, Luis FerramachoAbstract:: The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts z=/~1-5 are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial Non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the Non-Gaussianity parameter f(NL), with an error close to σ(f(NL))~1.
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cosmology on ultralarge scales with intensity mapping of the neutral hydrogen 21 cm emission limits on primordial non gaussianity
Physical Review Letters, 2013Co-Authors: Stefano Camera, Mario G Santos, Pedro G Ferreira, Luis FerramachoAbstract:The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts $z\ensuremath{\simeq}1--5$ are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial Non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the Non-Gaussianity parameter ${f}_{\mathrm{NL}}$, with an error close to ${\ensuremath{\sigma}}_{{f}_{\mathrm{NL}}}\ensuremath{\sim}1$.