Browsing by Author "Lai, Kwang-Chang"

Now showing 1 - 13 of 13

Classifying and probing flavor transition mechanisms of astrophysical high energy neutrinos
(2012-01-01)
Lai, Kwang-Chang
;
Lin, Guey-Lin
;
Liu, T. C.
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物理研究所
;
Institute of Physics
The future neutrino telescopes are expected to identify the flavors of astrophysical neutrinos and therefore determine the flavor ratio. The flavor ratio of astrophysical neutrinos observed at the Earth depends on both the initial flavor ratio at the source and flavor transitions taking place during the propagations of these neutrinos. We propose a model-independent way to parameterize the above flavor transitions, including standard oscillations and beyond. A systematical way is also described to probe those mechanisms taking advantage of R equivalent to phi(mu)/(phi(e) + phi(tau)) and S equivalent to phi(e)/phi(tau) the observables in neutrino telescope measurements.
Constraining the mass scale of a Lorentz-violating Hamiltonian with the measurement of astrophysical neutrino-flavor composition
(2017-12-26)
Lai, Kwang-Chang
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Lai, Wei-Hao
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Lin, Guey-Lin
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物理研究所
;
Institute of Physics
We study Lorentz violation effects on flavor transitions of high energy astrophysical neutrinos. It is shown that the appearance of a Lorentz-violating Hamiltonian can drastically change the flavor transition probabilities of astrophysical neutrinos. Predictions of Lorentz-violation effects on flavor compositions of astrophysical neutrinos arriving on Earth are compared with IceCube flavor composition measurement which analyzes astrophysical neutrino events in the energy range between 25 TeV and 2.8 PeV. Such a comparison indicates that the future IceCube-Gen2 will be able to place stringent constraints on a Lorentz-violating Hamiltonian in the neutrino sector. We work out the expected sensitivities by IceCube-Gen2 on dimension-3 CPT-odd and dimension-4 CPT-even operators in a Lorentz-violating Hamiltonian. The expected sensitivities can improve on the current constraints obtained from other types of experiments by more than two orders of magnitudes for certain ranges of the parameter space.
Determination of the neutrino flavor ratio at the astrophysical source
(2009-11-01)
Lai, Kwang-Chang
;
Lin, Guey-Lin
;
Liu, T. C.
;
物理研究所
;
Institute of Physics
We discuss the reconstruction of neutrino flavor ratios at astrophysical sources through the future neutrino-telescope measurements. Taking the ranges of neutrino mixing parameters theta(ij) as those given by the current global fit, we demonstrate by a statistical method that the accuracies in the measurements of energy-independent ratios R equivalent to phi(nu(mu))/(phi(nu(e))+phi(nu(tau))) and S equivalent to phi(nu(e))/phi(nu(tau)) among integrated neutrino flux should both be better than 10% in order to distinguish between the pion source and the muon-damped source at the 3 sigma level. The 10% accuracy needed for measuring R and S requires an improved understanding of the background atmospheric neutrino flux to a better than 10% level in the future. We discuss the applicability of our analysis to practical situations that the diffuse astrophysical neutrino flux arises from different types of sources and each point source has a neutrino flavor ratio varying with energies. We also discuss the effect of the leptonic CP phase on the flavor-ratio reconstruction.
Determinations of flavor ratios and flavor transitions of astrophysical neutrinos
(2010)
Lin, Guey-Lin
;
Liu, T. C.
;
Lai, Kwang-Chang
;
Huang, M. A.
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物理研究所
We argue that an effective flavor discrimination in neutrino telescopes is the key to probe the flavor ratios of astrophysical neutrinos at the source and flavor transition mechanisms of these neutrinos during their propagations from the source to the Earth. We first discuss how well one can reconstruct the flavor ratios of astrophysical neutrinos at the source. We then discuss how to probe flavor transition mechanisms of propagating astrophysical neutrinos. In this regard, we propose a model independent parametrization for neutrino flavor transitions, with the neutrino oscillation as a special case.
Flavor transition mechanisms of propagating astrophysical neutrinos: A model independent parametrization
(2010-11-05)
Lai, Kwang-Chang
;
Lin, Guey-Lin
;
Liu, T. C.
;
物理研究所
;
Institute of Physics
One of the important goals for future neutrino telescopes is to identify the flavors of astrophysical neutrinos and therefore determine the flavor ratio. The flavor ratio of astrophysical neutrinos observed on the Earth depends on both the initial flavor ratio at the source and flavor transitions taking place during propagations of these neutrinos. We propose a model independent parametrization for describing the above flavor transitions. A few flavor transition models are employed to test our parametrization. The observational test for flavor transition mechanisms through our parametrization is discussed.
Influence of plasma collective effects on cosmological evolution
(2008-06-28)
Lai, Kwang-Chang
;
Chen, Pisin
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物理研究所
;
Institute of Physics
It is well-known that the universe was in a plasma state both before decoupling and after reionization. However, the conventional wisdom has been that the plasma effects are largely Debye-shielded and can thus be safely ignored when considering large scale evolutions. Recently we showed that large scale structure formation in the universe may actually be suppressed by the plasma collective effect. Indeed, observational data indicate that the conventional theoretical formula tends to overestimate the matter power spectrum at scales k > 1hMpc(-1). In this paper, we further develop our theory through a more thorough and general derivation of the Maxwell-Einstein-Boltzmann equation. In addition to baryon density perturbation post reionization, we apply this general formulation to investigate the possible plasma effect on CMB anisotropy. As expected, while the plasma effect does render an observable effect to the former, its impact on the latter is totally negligible.
Neutrino flavor ratio on Earth and at astrophysical sources
(2010-04-01)
Lai, Kwang-Chang
;
Lin, Guey-Lin
;
Liu, T. C.
;
物理研究所
;
Institute of Physics
We present the reconstruction of neutrino flavor ratios at astrophysical sources. For distinguishing the pion source and the muon-damped source to the 3 a level, the neutrino flux ratios, R equivalent to phi(nu(mu))/(phi(nu(e)) + phi(nu(r))) and S equivalent to phi(nu(e))/(phi(nu(r))), need to be measured in accuracies better than 10%. (C) 2010 Elsevier B.V. All rights reserved.
NEUTRINO FLAVOR RATIOS ON EARTH UNDER DECAY AND OSCILLATION SCENARIOS
(2013)
Liu, T. C.
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Lai, Kwang-Chang
;
Lin, Guey-Lin
;
物理研究所
;
Institute of Physics
In the neutrino propagation mechanisms, both neutrino oscillation and decay mechanisms, the actual neutrinos flavor ratio at astrophysical sources can be quite different from observed ratios on Earth.(1) We introduce the recent global fitting result of the mixing angle values(2) into the analysis to point out the allowed neutrino flavor ratios on Earth for standard neutrino oscillation and general decay mechanisms. In this analysis, four types of the neutrino decay mechanisms can be separated from the oscillation case easily with arbitary initial neutrino flavor ratio and the other four types of neutrino decay mechanisms can be identified from the oscillation case with the specified source. The rest types of neutrino decays strongly overlape with the oscillation and cannot be identified.
NEUTRINO FLAVOR RATIOS ON THE EARTH FOR DECAY AND OSCILLATION SCENARIOS
(2013-01-20)
Liu, T. C.
;
Lai, Kwang-Chang
;
Lin, Guey-Lin
;
物理研究所
;
Institute of Physics
Due to flavor transition mechanisms in neutrino propagations, both neutrino oscillation and decay, neutrinos flavor ratio at astrophysical sources can quite different from observed ratios on the Earth.(1) We use the recent global fitting result of the mixing angle values(2) to determine the allowed neutrino flavor ratios on the Earth for standard neutrino oscillation and general decay mechanisms. In this analysis, four types of the neutrino decay mechanisms can be distinguished from the oscillation case easily with arbitrary initial neutrino flavor ratio and the other four types of neutrino decay mechanisms can be distinguished from the oscillation case with the specified source. The rest types of neutrino decays strongly overlap with the oscillation and cannot be identified.
On possibility of determining neutrino mass hierarchy by the charged-current and neutral-current events of supernova neutrinos in scintillation detectors
(2019-02-12)
Lee, Fei-Fan
;
Lee, Feng-Shiuh
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Lai, Kwang-Chang
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電機學院
;
College of Electrical and Computer Engineering
One of the unresolved mysteries in neutrino physics is the neutrino mass hierarchy. We present a new method to determine neutrino mass hierarchy by comparing the events of inverse beta decays (IBD), e+pn+e+, and neutral current (NC) interactions, ()+p()+p, of supernova neutrinos from accretion and cooling phases in scintillation detectors. Supernova neutrino flavor conversions depend on the neutrino mass hierarchy. On account of Mikheyev-Smirnov-Wolfenstein effects, the full swap of the e flux with the x (,) one occurs in the inverted hierarchy, while such a swap does not occur in the normal hierarchy. In consequence, the ratio of high energy IBD events to NC events for the inverted hierarchy is higher than in the normal hierarchy. Since the luminosity ofe is larger than that of x in accretion phase while the luminosity of e becomes smaller than that of x in cooling phase, we calculate this ratio for both accretion and cooling phases. By analyzing the change of this event ratio from accretion phase to cooling phase, one can determine the neutrino mass hierarchy.
Plasma suppression of large scale structure formation in the universe
(2007-12-07)
Chen, Pisin
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Lai, Kwang-Chang
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物理研究所
;
Institute of Physics
We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce an electrostatic pressure which, working together with the thermal pressure, would counter the gravitational collapse. As a result, the effective Jeans length, (lambda) over tilde (J) is increased by a factor (lambda) over tilde (J)/(lambda) over tilde (J) = root 8/5, relative to the conventional one. For scales smaller than the effective Jeans scale the plasma would oscillate at the ion-acoustic frequency. The modes that would be influenced by this effect lie roughly in the range 0.5h Mpc(-1)< k, which corresponds to the Lyman-alpha forest from the intergalactic medium. We predict that in the linear regime of density-contrast growth, the plasma suppression of the matter power spectrum would approach 1 - (Omega(dm)/Omega(m))(2) similar to 1 - (5/6)(2) similar to 30%.
Probing neutrino flavor transition mechanism with ultrahigh energy astrophysical neutrinos
(2014-02-06)
Lai, Kwang-Chang
;
Lin, Guey-Lin
;
Liu, Tsung-Che
;
物理研究所
;
Institute of Physics
Observation of ultrahigh energy astrophysical neutrinos and identification of their flavors have been proposed for future neutrino telescopes. The flavor ratio of astrophysical neutrinos observed on the Earth depends on both the initial flavor ratio at the source and flavor transitions taking place during propagations of these neutrinos. The flavor transition mechanisms are well classified with our model-independent parametrization. We find that a new parameter R equivalent to phi(e)/(phi(mu) + phi(tau)) can probe directly the flavor transition in the framework of our model-independent parametrization, without the assumption of the nu(mu)-nu(tau) symmetry. A few flavor-transition models are employed to test our parametrization with this new observable. The observational constraints on flavor transition mechanisms by the new observable are discussed through our model- independent parametrization.
Probing neutrino mass hierarchy by comparing the charged-current and neutral-current interaction rates of supernova neutrinos
(2016-07)
Lai, Kwang-Chang
;
Lee, Fei-Fan
;
Lee, Feng-Shiuh
;
Lin, Guey-Lin
;
Liu, Tsung-Che
The neutrino mass hierarchy is one of the neutrino fundamental properties yet to be determined. We introduce a method to determine neutrino mass hierarchy by comparing the interaction rate of neutral current (NC) interactions, nu((nu) over bar)+p -> v((v) over bar) +p, and inverse beta decays (IBD), (nu) over bar (e)+p -> n + e(+), of supernova neutrinos in scintillation detectors. Neutrino flavor conversions inside the supernova are sensitive to neutrino mass hierarchy. Due to Mikheyev-Smirnov-Wolfenstein effects, the full swapping of (nu) over bar (e) flux with the (nu) over bar (x)(x = mu, tau) one occurs in the inverted hierarchy, while such a swapping does not occur in the normal hierarchy. As a result, more high energy IBD events occur in the detector for the inverted hierarchy than the high energy IBD events in the normal hierarchy. By comparing IBD interaction rate with the mass hierarchy independent NC interaction rate, one can determine the neutrino mass hierarchy.