arXiv subjects

Cheng-Yang Lee

Publications and source records attributed to Cheng-Yang Lee.

36 records · Page 2Linked to original sources

arXiv2020

Cherenkov radiation in a strong magnetic field

According to quantum electrodynamics, in a strong magnetic field that is constant and spatially uniform, the vacuum becomes polarized with a refractive index greater than unity. As a result, ultra-relativistic charged particles travelling in such media can emit Cherenkov radiation with a power spectrum directly proportional to the photon frequency $ω$. Therefore, by extrapolating $ω$ beyond the critical synchrotron frequency $ω_{c}$, the Cherenkov radiation will eventually dominate over its synchrotron counterpart. However, such an extrapolation is not possible. We show that in the framework of effective field theory, the maximal attainable photon frequency $ω_{\tiny{\mbox{max}}}$ is about four order of magnitude less than $ω_{c}$. At $ω=ω_{\tiny{\mbox{max}}}$, given the $γ_{e}$-factor of an electron travelling normal to a constant and spatially uniform magnetic field $\mathbf{B}$, the spectrum of Cherenkov radiation becomes dominant when $γ_{e}(|\mathbf{B}|/\mbox{Gauss})\gtrsim 4.32\times 10^{19}$. Nevertheless, detecting the Cherenkov radiation in astrophysical environments remains challenging since its spectral flux density is about three orders of magnitude less than the synchrotron radiation.

hep-ph↗

arXiv2020

Interactions and oscillations of coherent flavor eigenstates in beta decay

The theory pioneered by Blasone and Vitiello describes massive neutrinos as generalized coherent flavor eigenstates within the extended Standard Model. In this paper, we compute the neutron beta decay spectrum for the Blasone-Vitiello theory in a model with two neutrinos. For relativistic neutrinos, the obtained spectrum is in agreement with the Standard Model. However, there are discrepancies when the kinetic energy of the electron is close to the end point energy. The possibility of measuring the discrepancies in future experiments is discussed.

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arXiv2019

Spin-half mass dimension one fermions and their higher-spin generalizations

A self-contained review on spin-half mass dimension one fermions and their higher-spin generalizations is presented. Starting from the two-component left-handed Weyl spinors, the Dirac spinors and Elko (eigenspinors of the charge conjugation operator) are constructed. After elaborating on their similarities and differences, we generalize the spin-half Elko to higher-spin. The field operators constructed from Elko and their higher-spin generalizations are shown to be of mass dimension one with positive-definite free Hamiltonians. The physical significance of higher-spin mass dimension one particles and further extensions in the context of Lounesto classification are discussed.

hep-th↗

arXiv2019

Magnetic field creation by solar mass neutrino jets

Parity violation and its effects for neutrinos in astrophysical contexts have been considered earlier in pioneering papers of Hawking and Vilenkin. But because even the largest magnetic moments predicted by physics beyond the Standard Model are some twelve orders of magnitude smaller than the Bohr magneton, their implications for magnetic field generation and neutrino oscillations are generally considered insignificant. Here we show that since in astrophysical scenarios a huge number of neutrinos may be emitted, the smallness of the magnetic moment, when coupled with parity violation, is compensated by the sheer number of neutrinos. The merger of neutron stars would leave behind a short pulse of electromagnetic synchrotron radiation even if the neutrino jet in the merger points away from the neutrino detectors. We show that the magnetic field can be as large as $10^6\,\mbox{Gauss}$ and comment on the possibility of direct detection. Observation of such a pulse would lend strong support for neutrino magnetic moments and resolve the missing neutrino problem in neutron star mergers.

astro-ph.HE↗

arXiv2017

A QFT-induced phase in neutrino flavour oscillations

In the extended Standard Model of particle physics, each neutrino mass eigenstate is predicted to have a tiny but non vanishing magnetic moment induced by quantum field theoretic corrections. These QFT-induced magnetic momenta depend linearly on masses of the underlying mass eigenstates with a proportionality constant ${3eG_{F}}/{(8\sqrt{2}π^{2})} $. As a consequence when neutrinos are embedded in an environment containing magnetic fields the flavour oscillations get a contribution from the induced relative phases.

hep-ph↗

arXiv2016

Constraints on mass dimension one fermionic dark matter from the Yukawa interaction

We study the loop corrections to the scalar propagator and the fermionic self-energy for the mass dimension one fermionic dark matter with the Yukawa interaction. We find, in the former case, there is a non-vanishing Lorentz-violating term while the later is Lorentz-invariant. Our study of the fermionic loop correction shows that unitarity demands the fermionic mass must be at least half of the bosonic mass and that the Lorentz-violating term makes a non-trivial correction to the bosonic propagator. We discuss what these results mean in the context of the Standard Model and the possibility of bypassing the unitarity constraint. In the simplest scenario, within the framework of standard quantum field theory, by identifying the scalar boson to be the Higgs boson with a mass of 125 GeV, the mass of the fermion must be at least 62.5 GeV.

hep-ph↗

arXiv2016

Spin and helicity of massive particles

It is a well-known fact that helicity is a Lorentz-invariant for massless but not for massive particles. Nevertheless, a satisfactory proof of this fact and a detailed analysis on the relative orientation between spin and the momentum are not readily available. One such analysis was presented by Wigner where a formula for the angle between the spin and the momentum is derived for massive particle states undergoing two successive boosts in orthogonal directions. In this note, using the Wigner rotation, an alternative derivation is provided.

hep-th↗

arXiv2016

Quantum field theory with a preferred direction: The very special relativity framework

The theory of very special relativity (VSR) proposed by Cohen and Glashow contains an intrinsic preferred direction. Starting from the irreducible unitary representation of the inhomogeneous VSR group $ISIM(2)$, we present a rigorous construction of quantum field theory with a preferred direction. We find, although the particles and their quantum fields between the VSR and Lorentz sectors are physically different, they share many similarities. The massive spin-half and spin-one vector fields are local and satisfy the Dirac and Proca equations respectively. This result can be generalised to higher-spin field theories. By studying the Yukawa and standard gauge interactions, we obtain a qualitative understanding on the effects of the preferred direction. Its effect is manifest for polarised processes but are otherwise absent.

hep-th↗

arXiv2015

Symmetries and unitary interactions of mass dimension one fermionic dark matter

The fermionic fields constructed from Elko have several unexpected properties. They satisfy the Klein-Gordon but not the Dirac equation and are of mass dimension one instead of three-half. Starting with the Klein-Gordon Lagrangian, we initiate a careful study of the symmetries and interactions of these fermions and their higher-spin generalisations. We find, although the fermions are of mass dimension one, the four-point fermionic self-interaction violates unitarity at high-energy. Therefore, it cannot be a fundamental interaction of the theory. It follows that for the spin-half fermions, the demand of renormalisability and unitarity forbids four-point interactions and only allows for the Yukawa interaction. For fermions with spin j>1/2, they have no renormalisable or unitary interactions. Since the theory is described by a Klein-Gordon Lagrangian, the interaction generated by the local $U(1)$ gauge symmetry which contains a four-point interaction, is excluded by the demand of renormalisability. In the context of the Standard Model, these properties make the spin-half fermions natural dark matter candidates.

hep-th↗

arXiv2015

Massive fermions in 2+1 dimensions

We construct the higher-spin massive fermionic fields in 2+1 dimensions. Their field equations and propagators are derived from first principle. For fields with j>1/2, complications arise from the non-linear behaviour of the boost operators. We find that for a spin-three-half field, the non-linearity have an underlying structure that guarantees the locality of the fields and the existence of covariant propagators. We conjecture that this structure exists for fields of all spin.

hep-th↗

arXiv2015

Self-interacting mass-dimension one fields for any spin

According to Ahluwalia and Grumiller, massive spin-half fields of mass-dimension one can be constructed using the eigenspinors of the charge-conjugation operator (Elko) as expansion coefficients. In this paper, we generalize their result by constructing quantum fields from higher-spin Elko. The kinematics of these fields are thoroughly investigated. Starting with the field operators, their propagators and Hamiltonians are derived. These fields satisfy the higher-spin generalization of the Klein-Gordon but not the Dirac equation. Independent of the spin, they are all of mass-dimension one and are thus endowed with renormalizable self-interactions. These fields violate Lorentz symmetry. The violation can be characterized by a non Lorentz-covariant term that appears in the Elko spin-sums. This term provides a decomposition of the generalized higher-spin Dirac operator in the momentum space thus suggesting a possible connection between the mass-dimension one fields and the Lorentz-invariant fields.

hep-th↗

arXiv2015

Elko in 1+1 dimensions

The quantum field operator for spin-half Elko describes a massive self-interacting fermionic dark matter candidate of mass dimension one. It has been shown that the theory has a built-in violation of the Lorentz symmetry and a well-defined element of non-locality in the form of a preferred direction. This note shows that quantum field operators constructed using spin-half and higher-spin Elko violate Lorentz symmetry from first principle. Subsequently, we study the kinematics of Elko and its quantum field operator for any spin along the preferred direction.

hep-th↗

arXiv2014

The Lagrangian for mass dimension one fermionic dark matter

The mass dimension one fermionic field associated with Elko satisfies the Klein-Gordon but not the Dirac equation. However, its propagator is not a Green's function of the Klein-Gordon operator. We determine the operator in which the associated Green's function is the propagator of the fermionic field. The field is still of mass dimension one, but the obtained Lagrangian resolves the last outstanding issue of mass dimension one fields. This Lagrangian does not admit local gauge invariance. Therefore, the mass dimension one fermions have limited interactions with the Standard Model particles and are natural dark matter candidates.

hep-th↗

arXiv2013

Symmetries of Elko and massive vector fields

This thesis studies the symmetries and phenomenologies of the massive vector fields of indefinite spin with both scalar and spin-one degrees of freedom and Elko. The investigation is conducted by using and extending the quantum field theory formalism developed by Wigner and Weinberg. In particular, we explore the possibility that the W^{\pm} and Z bosons have an additional scalar degree of freedom and show that Elko is a fermionic dark matter candidate. We show that the massive vector fields of indefinite spin are consistent with Poincare symmetry and have physically desirable properties that are absent for their pure spin-one counterpart. Using the new vector fields, the decay of the W^{\pm} and Z bosons to leptons at tree-level are in agreement with the Standard Model (SM) predictions. For higher order scattering amplitudes, the theory has better convergent behaviour than the intermediate vector boson model and the Fermi theory. Elko has the unusual property that it satisfies the Klein-Gordon but not the Dirac equation and has mass dimension one instead of three-half. We show that the Elko fields are local only along a preferred axis and that they violate Lorentz symmetry. Motivated by the results obtained by Ahluwalia and Horvath that the Elko spin-sums are covariant under very special relativity (VSR) transformations, we derive the VSR particle states and quantum fields. We show that the VSR particles can only interact with the SM particles through gravity and massive scalar particles thus making them and hence Elko dark matter candidates.

hep-th↗

arXiv2012

Gamma-ray bursts and the relevance of rotation-induced neutrino sterilization

A la Pontecorvo when one defines electroweak flavour states of neutrinos as a linear superposition of mass eigenstates one ignores the associated spin. If, however, there is a significant rotation between the neutrino source, and the detector, a negative helicity state emitted by the former acquires a non-zero probability amplitude to be perceived as a positive helicity state by the latter. Both of these states are still in the left-Weyl sector of the Lorentz group. The electroweak interaction cross sections for such helicity-flipped states are suppressed by a factor of $(m_ν/E_ν)^2$, where $m_ν$ is the expectation value of the neutrino mass, and $E_ν$ is the associated energy. Thus, if the detecting process is based on electroweak interactions, and the neutrino source is a highly rotating object, the rotation-induced helicity flip becomes very significant in interpreting the data. The effect immediately generalizes to anti-neutrinos. Motivated by these observations we present a generalization of the Pontecorvo formalism and discuss its relevance in the context of recent data obtained by the IceCube neutrino telescope.

hep-ph↗

arXiv2010

Elko as self-interacting fermionic dark matter with axis of locality

We here provide further details on the construction and properties of mass dimension one quantum fields based on Elko expansion coefficients. We show that by a judicious choice of phases, the locality structure can be dramatically improved. In the process we construct a fermionic dark matter candidate which carries not only an unsuppressed quartic self interaction but also a preferred axis. Both of these aspects are tentatively supported by the data on dark matter.

hep-th↗

arXiv2009

Self-interacting Elko dark matter with an axis of locality

This communication is a natural and nontrivial continuation of the 2005 work of Ahluwalia and Grumiller on Elko. Here we report that Elko breaks Lorentz symmetry in a rather subtle and unexpected way by containing a `hidden' preferred direction. Along this preferred direction, a quantum field based on Elko enjoys locality. In the form reported here, Elko offers a mass dimension one fermionic dark matter with a quartic self-interaction and a preferred axis of locality. The locality result crucially depends on a judicious choice of phases.

hep-ph↗

arXiv2008

Dark matter and dark gauge fields

Following the unexpected theoretical discovery of a mass dimension one fermionic quantum field of spin one half, we now present first results on two _local_ versions. The Dirac and Majorana fields of the standard model of particle physics are supplemented by their natural counterparts in the dark matter sector. The possibility that a mass dimension transmuting symmetry may underlie a new standard model of particle physics is briefly suggested.

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