67 research outputs found
Addressing the Majorana vs. Dirac Question with Neutrino Decays
The Majorana versus Dirac nature of neutrinos remains an open question. This
is due, in part, to the fact that virtually all the experimentally accessible
neutrinos are ultra-relativistic. Noting that Majorana neutrinos can behave
quite differently from Dirac ones when they are non-relativistic, we show that,
at leading order, the angular distribution of the daughters in the decay of a
heavy neutrino into a lighter one and a self-conjugate boson is isotropic in
the parent's rest frame if the neutrinos are Majorana, independent of the
parent's polarization. If the neutrinos are Dirac fermions, this is, in
general, not the case. This result follows from CPT invariance and is
independent of the details of the physics responsible for the decay. We explore
the feasibility of using these angular distributions -- or, equivalently, the
energy distributions of the daughters in the laboratory frame -- in order to
address the Majorana versus Dirac nature of neutrinos if a fourth, heavier
neutrino mass eigenstate reveals itself in the current or next-generation of
high-energy colliders, intense meson facilities, or neutrino beam experiments.Comment: 11 pages, 3 figure
Spin-flavor precession of Dirac neutrinos in dense matter and its potential in core-collapse supernovae
We calculate the spin-flavor precession (SFP) of Dirac neutrinos induced by
strong magnetic fields and finite neutrino magnetic moments in dense matter. As
found in the case of Majorana neutrinos, the SFP of Dirac neutrinos is enhanced
by the large magnetic field potential and suppressed by large matter potentials
composed of the baryon density and the electron fraction. The SFP is possible
irrespective of the large baryon density when the electron fraction is close to
1/3. The diagonal neutrino magnetic moments that are prohibited for Majorana
neutrinos enable the spin precession of Dirac neutrinos without any flavor
mixing. With supernova hydrodynamics simulation data, we discuss the
possibility of the SFP of both Dirac and Majorana neutrinos in core-collapse
supernovae. The SFP of Dirac neutrinos occurs at a radius where the electron
fraction is 1/3. The required magnetic field of the proto-neutron star for the
SFP is a few G at any explosion time. For the Majorana neutrinos, the
required magnetic field fluctuates from G to G. Such a
fluctuation of the magnetic field is more sensitive to the numerical scheme of
the neutrino transport in the supernova simulation.Comment: 14 pages, 10 figure
Collective neutrino oscillations on a quantum computer with hybrid quantum-classical algorithm
We simulate the time evolution of collective neutrino oscillations in
two-flavor settings on a quantum computer. We explore the generalization of
Trotter-Suzuki approximation to time-dependent Hamiltonian dynamics. The
trotterization steps are further optimized using the Cartan decomposition of
two-qubit unitary gates U SU (4) in the minimum number of controlled-NOT
(CNOT) gates making the algorithm more resilient to the hardware noise. A more
efficient hybrid quantum-classical algorithm is also explored to solve the
problem on noisy intermediate-scale quantum (NISQ) devices.Comment: 9 pages, 10 figure
Axion Production from Landau Quantization in the Strong Magnetic Field of Magnetars
We utilize an exact quantum calculation to explore axion emission from
electrons and protons in the presence of the strong magnetic field of
magnetars. The axion is emitted via transitions between the Landau levels
generated by the strong magnetic field. The luminosity of axions emitted by
protons is shown to be much larger than that of electrons and becomes stronger
with increasing matter density. Cooling by axion emission is shown to be much
larger than neutrino cooling by the Urca processes. Consequently, axion
emission in the crust may significantly contribute to the cooling of magnetars.
In the high-density core, however, it may cause heating of the magnetar.Comment: 14 pages, 3 figure
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