1804.10395
Lethal radiation from nearby supernovae helps to explain the small cosmological constant
Totani, et al
The observed value Lambda_obs of the cosmological constant Lambda is extremely smaller than theoretical expectations, and the anthropic argument has been proposed as a solution to this problem because galaxies do not form when Lambda >> Lambda_obs. However, the contemporary galaxy formation theory predicts that stars form even when a high value of Lambda / Lambda_obs ~50, which makes the anthropic argument less persuasive. Here, calculate the probability distribution of Lambda using a model of cosmological galaxy formation, considering extinction of observers caused by radiation from nearby supernovae. The life survival probability decreases in a large Lambda universe because of higher stellar density. Using a reasonable rate of lethal supernovae, find that the mean expectation value of Lambda can be close to Lambda_obs, and hence tis effect may be essential to understand the small but nonzero value of Lambda. It is predicted that we are located on the edge of habitable regions about stellar density, which may be tested in future exoplanet studies.
1804.10401
A technique for estimating the absolute gain of a photomultiplier tube
Takahashi, et al
Detection of low-intensity light relies on the conversion of photons to photoelectron, which are then multiplied and detected as an electrical signal. To measure the actual intensity of the light, one must know the factor by which the photoelectrons have been multiplied. To obtain this amplification factor, we have developed a procedure for estimating precisely the signal caused by a single photoelectron. The method utilizes the fact that the photoelectrons conform to a Poisson distribution. The average signal produced by a single photoelectron can then be estimated from the number of noise events, without requiring analysis of the distribution of the signal produced by a single photoelectron. The signal produced by one or more photoelectrons can be estimated experimentally without any assumptions. This technique, and an example of the analysis of a signal from a photomultiplier tube, are described in this study.
1804.10663
Survey geometry and the internal consistency of recent cosmic shear measurements
Troxel, Krause, Chang, Eifler, et al
Explore the impact of an update to the typical approximation for the shape noise term in the analytic covariance matrix for cosmic shear experiments that assumes the absence of survey boundary and mask effects. Present an exact expression for the number of galaxy pairs in this term based on the survey mask, which leads to more than a factor of 3 increase in the shape noise on the largest measured scales for KiDS-450 real-space cosmic shear data. Compare the result of this analytic expression to several alternative methods for measuring the shape noise from the data and find excellent agreement. This update to the covariance resolves any internal model tension evidenced but the previously large cosmological best-fit chi^2 for the KiDS-450 cosmic shear data. The best-fit chi^2 is reduced from 161 to 121 for 118 degrees of freedom. Also apply a correction to how the multiplicative shear calibration uncertainty is included in the covariance. This change, along with a previously known update to the reported effective angular values of the data vector, jointly shift the inferred amplitude of the correlation function to higher values. Find that this improves agreement of the KiDS-450 cosmic shear results with DES-Y1 and Planck results.
Lethal radiation from nearby supernovae helps to explain the small cosmological constant
Totani, et al
The observed value Lambda_obs of the cosmological constant Lambda is extremely smaller than theoretical expectations, and the anthropic argument has been proposed as a solution to this problem because galaxies do not form when Lambda >> Lambda_obs. However, the contemporary galaxy formation theory predicts that stars form even when a high value of Lambda / Lambda_obs ~50, which makes the anthropic argument less persuasive. Here, calculate the probability distribution of Lambda using a model of cosmological galaxy formation, considering extinction of observers caused by radiation from nearby supernovae. The life survival probability decreases in a large Lambda universe because of higher stellar density. Using a reasonable rate of lethal supernovae, find that the mean expectation value of Lambda can be close to Lambda_obs, and hence tis effect may be essential to understand the small but nonzero value of Lambda. It is predicted that we are located on the edge of habitable regions about stellar density, which may be tested in future exoplanet studies.
1804.10401
A technique for estimating the absolute gain of a photomultiplier tube
Takahashi, et al
Detection of low-intensity light relies on the conversion of photons to photoelectron, which are then multiplied and detected as an electrical signal. To measure the actual intensity of the light, one must know the factor by which the photoelectrons have been multiplied. To obtain this amplification factor, we have developed a procedure for estimating precisely the signal caused by a single photoelectron. The method utilizes the fact that the photoelectrons conform to a Poisson distribution. The average signal produced by a single photoelectron can then be estimated from the number of noise events, without requiring analysis of the distribution of the signal produced by a single photoelectron. The signal produced by one or more photoelectrons can be estimated experimentally without any assumptions. This technique, and an example of the analysis of a signal from a photomultiplier tube, are described in this study.
1804.10663
Survey geometry and the internal consistency of recent cosmic shear measurements
Troxel, Krause, Chang, Eifler, et al
Explore the impact of an update to the typical approximation for the shape noise term in the analytic covariance matrix for cosmic shear experiments that assumes the absence of survey boundary and mask effects. Present an exact expression for the number of galaxy pairs in this term based on the survey mask, which leads to more than a factor of 3 increase in the shape noise on the largest measured scales for KiDS-450 real-space cosmic shear data. Compare the result of this analytic expression to several alternative methods for measuring the shape noise from the data and find excellent agreement. This update to the covariance resolves any internal model tension evidenced but the previously large cosmological best-fit chi^2 for the KiDS-450 cosmic shear data. The best-fit chi^2 is reduced from 161 to 121 for 118 degrees of freedom. Also apply a correction to how the multiplicative shear calibration uncertainty is included in the covariance. This change, along with a previously known update to the reported effective angular values of the data vector, jointly shift the inferred amplitude of the correlation function to higher values. Find that this improves agreement of the KiDS-450 cosmic shear results with DES-Y1 and Planck results.
No comments:
Post a Comment