The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Atsushi Naruko - One of the best experts on this subject based on the ideXlab platform.
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anisotropic inflation reexamined upper bound on broken Rotational Invariance during inflation
Journal of Cosmology and Astroparticle Physics, 2015Co-Authors: Atsushi Naruko, Eiichiro Komatsu, Masahide YamaguchiAbstract:The presence of a light vector field coupled to a scalar field during inflation makes a distinct prediction: the observed correlation functions of the cosmic microwave background (CMB) become statistically anisotropic. We study the implications of the current bound on statistical anisotropy derived from the Planck 2013 CMB temperature data for such a model. The previous calculations based on the attractor solution indicate that the magnitude of anisotropy in the power spectrum is proportional to N2, where N is the number of e-folds of inflation counted from the end of inflation. In this paper, we show that the attractor solution is not necessarily compatible with the current bound, and derive new predictions using another branch of anisotropic inflation. In addition, we improve upon the calculation of the mode function of perturbations by including the leading-order slow-roll corrections. We find that the anisotropy is roughly proportional to [2(?H+4?H)/3?4(c?1)]?2, where ?H and ?H are the usual slow-roll parameters and c is the parameter in the model, regardless of the form of potential of an inflaton field. The bound from Planck implies that breaking of Rotational Invariance during inflation (characterized by the background homogeneous shear divided by the Hubble rate) is limited to be less than (10?9). This bound is many orders of magnitude smaller than the amplitude of breaking of time translation Invariance, which is observed to be (10?2).
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anisotropic inflation reexamined upper bound on broken Rotational Invariance during inflation
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Atsushi Naruko, Eiichiro Komatsu, Masahide YamaguchiAbstract:The presence of a light vector field coupled to a scalar field during inflation makes a distinct prediction: the observed correlation functions of the cosmic microwave background (CMB) become statistically anisotropic. We study the implications of the current bound on statistical anisotropy derived from the Planck 2013 CMB temperature data for such a model. The previous calculations based on the attractor solution indicate that the magnitude of anisotropy in the power spectrum is proportional to $N^2$, where $N$ is the number of $e$-folds of inflation counted from the end of inflation. In this paper, we show that the attractor solution is not compatible with the current bound, and derive new predictions using another branch of anisotropic inflation. In addition, we improve upon the calculation of the mode function of perturbations by including the leading-order slow-roll corrections. We find that the anisotropy is roughly proportional to $[2(\varepsilon_H+4\eta_H)/3-4(c-1)]^{-2}$, where $\varepsilon_H$ and $\eta_H$ are the usual slow-roll parameters and $c$ is the parameter in the model, regardless of the form of potential of an inflaton field. The bound from Planck implies that breaking of Rotational Invariance during inflation (characterized by the background homogeneous shear divided by the Hubble rate) is limited to be less than ${\cal O}(10^{-9})$. This bound is many orders of magnitude smaller than the amplitude of breaking of time translation Invariance, which is observed to be ${\cal O}(10^{-2})$.
M D Trott - One of the best experts on this subject based on the ideXlab platform.
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Rotational Invariance of trellis codes i encoders and precoders
IEEE Transactions on Information Theory, 1996Co-Authors: M D Trott, S Benedetto, R Garello, Marina MondinAbstract:We present a theoretical framework for Rotational Invariance of trellis codes. The distinction between codes and encoders plays a pivotal role. Necessary and sufficient conditions for Rotational Invariance are derived under general assumptions, and a construction is presented that obtains a Rotationally invariant encoder for almost any Rotationally invariant code, independent of the code's algebraic structure. Encoders that use a differential precoder are considered as a separate case, where a system-theoretic characterization of precoding is used to find two alternative and slightly less general encoder constructions.
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Rotational Invariance of trellis codes ii group codes and decoders
IEEE Transactions on Information Theory, 1996Co-Authors: S Benedetto, R Garello, Marina Mondin, M D TrottAbstract:For pt.I see ibid., vol.42, no.3, p.751-65 (1996). In Part I, general results on Rotationally invariant codes and encoders were derived assuming no algebraic structure. In Part II, trellis codes based on group systems are considered as a special case for which code and encoder constructions are particularly simple. Rotational Invariance is expressed as an algebraic constraint on a group code, and algebraic constructions are found for both "absorbed precoder" encoders and for encoders with separate differential precoders. Finally, the various encoder forms used to achieve Rotational Invariance are compared based on their performance on an AWGN channel.
Marina Mondin - One of the best experts on this subject based on the ideXlab platform.
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Rotational Invariance of trellis codes i encoders and precoders
IEEE Transactions on Information Theory, 1996Co-Authors: M D Trott, S Benedetto, R Garello, Marina MondinAbstract:We present a theoretical framework for Rotational Invariance of trellis codes. The distinction between codes and encoders plays a pivotal role. Necessary and sufficient conditions for Rotational Invariance are derived under general assumptions, and a construction is presented that obtains a Rotationally invariant encoder for almost any Rotationally invariant code, independent of the code's algebraic structure. Encoders that use a differential precoder are considered as a separate case, where a system-theoretic characterization of precoding is used to find two alternative and slightly less general encoder constructions.
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Rotational Invariance of trellis codes ii group codes and decoders
IEEE Transactions on Information Theory, 1996Co-Authors: S Benedetto, R Garello, Marina Mondin, M D TrottAbstract:For pt.I see ibid., vol.42, no.3, p.751-65 (1996). In Part I, general results on Rotationally invariant codes and encoders were derived assuming no algebraic structure. In Part II, trellis codes based on group systems are considered as a special case for which code and encoder constructions are particularly simple. Rotational Invariance is expressed as an algebraic constraint on a group code, and algebraic constructions are found for both "absorbed precoder" encoders and for encoders with separate differential precoders. Finally, the various encoder forms used to achieve Rotational Invariance are compared based on their performance on an AWGN channel.
Masahide Yamaguchi - One of the best experts on this subject based on the ideXlab platform.
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anisotropic inflation reexamined upper bound on broken Rotational Invariance during inflation
Journal of Cosmology and Astroparticle Physics, 2015Co-Authors: Atsushi Naruko, Eiichiro Komatsu, Masahide YamaguchiAbstract:The presence of a light vector field coupled to a scalar field during inflation makes a distinct prediction: the observed correlation functions of the cosmic microwave background (CMB) become statistically anisotropic. We study the implications of the current bound on statistical anisotropy derived from the Planck 2013 CMB temperature data for such a model. The previous calculations based on the attractor solution indicate that the magnitude of anisotropy in the power spectrum is proportional to N2, where N is the number of e-folds of inflation counted from the end of inflation. In this paper, we show that the attractor solution is not necessarily compatible with the current bound, and derive new predictions using another branch of anisotropic inflation. In addition, we improve upon the calculation of the mode function of perturbations by including the leading-order slow-roll corrections. We find that the anisotropy is roughly proportional to [2(?H+4?H)/3?4(c?1)]?2, where ?H and ?H are the usual slow-roll parameters and c is the parameter in the model, regardless of the form of potential of an inflaton field. The bound from Planck implies that breaking of Rotational Invariance during inflation (characterized by the background homogeneous shear divided by the Hubble rate) is limited to be less than (10?9). This bound is many orders of magnitude smaller than the amplitude of breaking of time translation Invariance, which is observed to be (10?2).
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anisotropic inflation reexamined upper bound on broken Rotational Invariance during inflation
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Atsushi Naruko, Eiichiro Komatsu, Masahide YamaguchiAbstract:The presence of a light vector field coupled to a scalar field during inflation makes a distinct prediction: the observed correlation functions of the cosmic microwave background (CMB) become statistically anisotropic. We study the implications of the current bound on statistical anisotropy derived from the Planck 2013 CMB temperature data for such a model. The previous calculations based on the attractor solution indicate that the magnitude of anisotropy in the power spectrum is proportional to $N^2$, where $N$ is the number of $e$-folds of inflation counted from the end of inflation. In this paper, we show that the attractor solution is not compatible with the current bound, and derive new predictions using another branch of anisotropic inflation. In addition, we improve upon the calculation of the mode function of perturbations by including the leading-order slow-roll corrections. We find that the anisotropy is roughly proportional to $[2(\varepsilon_H+4\eta_H)/3-4(c-1)]^{-2}$, where $\varepsilon_H$ and $\eta_H$ are the usual slow-roll parameters and $c$ is the parameter in the model, regardless of the form of potential of an inflaton field. The bound from Planck implies that breaking of Rotational Invariance during inflation (characterized by the background homogeneous shear divided by the Hubble rate) is limited to be less than ${\cal O}(10^{-9})$. This bound is many orders of magnitude smaller than the amplitude of breaking of time translation Invariance, which is observed to be ${\cal O}(10^{-2})$.
S Benedetto - One of the best experts on this subject based on the ideXlab platform.
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Rotational Invariance of trellis codes i encoders and precoders
IEEE Transactions on Information Theory, 1996Co-Authors: M D Trott, S Benedetto, R Garello, Marina MondinAbstract:We present a theoretical framework for Rotational Invariance of trellis codes. The distinction between codes and encoders plays a pivotal role. Necessary and sufficient conditions for Rotational Invariance are derived under general assumptions, and a construction is presented that obtains a Rotationally invariant encoder for almost any Rotationally invariant code, independent of the code's algebraic structure. Encoders that use a differential precoder are considered as a separate case, where a system-theoretic characterization of precoding is used to find two alternative and slightly less general encoder constructions.
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Rotational Invariance of trellis codes ii group codes and decoders
IEEE Transactions on Information Theory, 1996Co-Authors: S Benedetto, R Garello, Marina Mondin, M D TrottAbstract:For pt.I see ibid., vol.42, no.3, p.751-65 (1996). In Part I, general results on Rotationally invariant codes and encoders were derived assuming no algebraic structure. In Part II, trellis codes based on group systems are considered as a special case for which code and encoder constructions are particularly simple. Rotational Invariance is expressed as an algebraic constraint on a group code, and algebraic constructions are found for both "absorbed precoder" encoders and for encoders with separate differential precoders. Finally, the various encoder forms used to achieve Rotational Invariance are compared based on their performance on an AWGN channel.
