arXiv subjects

Xun-Jie Xu

Publications and source records attributed to Xun-Jie Xu.

85 records · Page 5Linked to original sources

arXiv2017

Coherent Neutrino-Nucleus Scattering and new Neutrino Interactions

We investigate the potential to probe new neutrino physics with future experiments measuring coherent neutrino-nucleus scattering. Experiments with high statistics should become feasible soon and allow to constrain parameters with unprecedented precision. Using a benchmark setup for a future experiment probing reactor neutrinos, we study the sensitivity on neutrino non-standard interactions and new exotic neutral currents (scalar, tensor, etc). Compared to Fermi interaction, percent and permille level strengths of the new interactions can be probed, superseding for some observables the limits from future neutrino oscillation experiments by up to two orders of magnitude.

hep-ph↗

arXiv2016

Minima of the Scalar Potential in the Type II Seesaw Model: From Local to Global

The Type II seesaw model requires that its scalar doublet $H$ and triplet $Δ$ get specific patterns of VEVs $\langle H\rangle\propto(0,1)^{T}$ and $\langleΔ\rangle\propto(0,0,1)^{T}$ to accommodate neutrino masses. However, other types of minima could also exist in the scalar potential, which may strongly contradict to experimental observations. This paper studies when the minimum at $\langle H\rangle\propto(0,1)^{T}$ and $\langleΔ\rangle\propto(0,0,1)^{T}$ will be global and finds the necessary and sufficient condition for that, assuming that the lepton number violating term $H^{2}Δ$ in the potential is perturbatively small.

hep-ph↗

arXiv2016

Connecting Leptonic Unitarity Triangle to Neutrino Oscillation with CP Violation in Vacuum and in Matter

Leptonic unitarity triangle (LUT) provides fundamental means to geometrically describe CP violation in neutrino oscillation. In this work, we use LUT to present a new geometrical interpretation of the vacuum oscillation probability, and derive a compact new oscillation formula in terms of only 3 independent parameters of the corresponding LUT. Then, we systematically study matter effects in the geometrical formulation of neutrino oscillation with CP violation. Including nontrivial matter effects, we derive a very compact new oscillation formula by using the LUT formulation. We further demonstrate that this geometrical formula holds well for applications to neutrino oscillations in matter, including the long baseline experiments T2K, MINOS, NOvA, and DUNE.

hep-ph↗

arXiv2016

Sterile neutrinos in the light of IceCube

We determine constraints on parameters of a single eV-scale light neutrino using IceCube-59 data. Particular emphasis is put on the question whether such an analysis can rule out sterile neutrino hints. While important complementary information is provided, the different dependence on the various sterile neutrino mixing angles makes it currently not possible to fully exclude short baseline appearance results or sterile neutrinos in general.

hep-ph↗

arXiv2015

Origin of Constrained Maximal CP Violation in Flavor Symmetry

Current data from neutrino oscillation experiments are in good agreement with $δ=-\fracπ{2}$ and $θ_{23}^{} = \fracπ{4}$. We define the notion of "constrained maximal CP violation" (CMCPV) for predicting these features and study their origin in flavor symmetry. We derive the parametrization-independent solution of CMCPV and give a set of equivalent definitions for it. We further present a theorem on how the CMCPV can be realized. This theorem takes advantage of residual symmetries in the neutrino and charged lepton mass matrices, and states that, up to a few minor exceptions, $(|δ|, θ_{23}) =(\fracπ{2}, \fracπ{4})$ is generated when those symmetries are real. The often considered $μ$-$τ$ reflection symmetry, as well as specific discrete subgroups of O(3), are special cases of our theorem.

hep-ph↗

arXiv2015

Why Is The Neutrino Oscillation Formula Expanded In $Δm_{21}^{2}/Δm_{31}^{2}$ Still Accurate Near The Solar Resonance In Matter?

The conventional approximate formula for neutrino oscillation in matter which is obtained from the expansion in terms of the ratio of mass square differences $α=Δm_{21}^{2}/Δm_{31}^{2}\approx0.03$, first proposed by Cervera, et al and Freund, turns out to be an accurate formula for accelerator neutrino experiments. Originally it required the neutrino energy to be well above the solar resonance to validate the expansion but it is found to be still very accurate when the formula is extrapolated to the resonance, which is practically important for the T2K experiment. This paper shows that the accuracy is guaranteed by cancellations of branch cut singularities and also, for the first time, analytically computes the actual error of the formula. The actual error implies that the original requirement can be safely removed in current experiments.

hep-ph↗

arXiv2015

A left-right symmetric flavor symmetry model

We discuss flavor symmetries in left-right symmetric theories. We show that such frameworks are a different environment for flavor symmetry model building compared to the usually considered cases. This does not only concern the need to obey the enlarged gauge structure, but also more subtle issues with respect to residual symmetries. Furthermore, if the discrete left-right symmetry is charge conjugation, potential inconsistencies between the flavor and charge conjugation symmetries should be taken care of. In our predictive model based on $A_4$ we analyze the correlations between the smallest neutrino mass, the atmospheric mixing angle and the Dirac CP phase, the latter prefers to lie around maximal values. There is no lepton flavor violation from the Higgs bi-doublet.

hep-ph↗

arXiv2015

Robustness of Neutrino Mass Matrix Predictions

We investigate the stability of neutrino mass matrix predictions on important and currently unknown observables. Those are the octant of $θ_{23}$, the sign of $\sinδ$ and the neutrino mass ordering. Determining those unknowns is expected to be useful in order to distinguish neutrino mass models. Therefore it may be interesting to know how robust the predictions of a mass matrix for the octant of $θ_{23}$ or the neutrino mass ordering are. By applying general multiplicative perturbations we explicitly quantify how probable it is that a perturbed mass matrix predicts an octant of $θ_{23}$ different from the original mass matrix, or even a neutrino mass ordering different from the original one. Both the general case and an explicit flavor symmetry model are studied. We give the probabilities as a function of the smallest neutrino mass, showing that for values exceeding 0.1 eV the chance to switch the prediction quickly approaches $50\,\%$.

hep-ph↗

arXiv2015

Origin of Symmetric PMNS and CKM Matrices

The PMNS and CKM matrices are phenomenologically close to symmetric, and a symmetric form could be used as zeroth-order approximation for both matrices. We study the possible theoretical origin of this feature in flavor symmetry models. We identify necessary geometric properties of discrete flavor symmetry groups that can lead to symmetric mixing matrices. Those properties are actually very common in discrete groups such as $A_{4}$, $S_{4}$ or $Δ(96)$. As an application of our theorem, we generate a symmetric lepton mixing scheme with $θ_{12}=θ_{23}=36.21^{\circ};θ_{13}=12.20^{\circ}$ and $δ=0$, realized with the group $Δ(96)$.

hep-ph↗

arXiv2014

Constraining Astrophysical Neutrino Flavor Composition from Leptonic Unitarity

The recent IceCube observation of ultra-high-energy astrophysical neutrinos has begun the era of neutrino astronomy. In this work, using the unitarity of leptonic mixing matrix, we derive nontrivial unitarity constraints on the flavor composition of astrophysical neutrinos detected by IceCube. Applying leptonic unitarity triangles, we deduce these unitarity bounds from geometrical conditions, such as triangular inequalities. These new bounds generally hold for three flavor neutrinos, and are independent of any experimental input or the pattern of leptonic mixing. We apply our unitarity bounds to derive general constraints on the flavor compositions for three types of astrophysical neutrino sources (and their general mixture), and compare them with the IceCube measurements. Furthermore, we prove that for any sources without $ν_τ$ neutrinos, a detected $ν_μ$ flux ratio $< 1/4$ will require the initial flavor composition with more $ν_e$ neutrinos than $ν_μ$ neutrinos.

hep-ph↗

arXiv2014

Connecting Leptonic Unitarity Triangle to Neutrino Oscillation

Leptonic unitarity triangle (LUT) provides a geometric description of CP violations in the lepton-neutrino sector and is directly measurable in principle. In this work, we reveal that the angles in the LUT have definite physical meaning, and demonstrate the exact connection of the LUT to neutrino oscillations. For the first time, we prove that these leptonic angles act as phase shifts in neutrino oscillations, by shifting Δm^{2}L/2E to Δm^{2}L/2E + α, where (L, E, α) denote the baseline length, neutrino energy and corresponding angle of the LUT. Each LUT has three independent parameters and contains only partial information of the PMNS matrix. We demonstrate that the partial information in each LUT can describe the corresponding neutrino oscillation. Hence, for the first time, we uncover that any given kind of neutrino oscillations contain at most three (rather than four) independent degrees of freedom from the PMNS matrix. This may provide a cleaner way for fitting the corresponding oscillation data.

hep-ph↗

arXiv2013

Introduction of the CDEX experiment

Weakly Interacting Massive Particles (WIMPs) are the candidates of dark matter in our universe. Up to now any direct interaction of WIMP with nuclei has not been observed yet. The exclusion limits of the spin-independent cross section of WIMP-nucleon which have been experimentally obtained is about 10^{-7}pb at high mass region and only 10^{-5}pb} at low mass region. China Jin-Ping underground laboratory CJPL is the deepest underground lab in the world and provides a very promising environment for direct observation of dark matter. The China Dark Matter Experiment (CDEX) experiment is going to directly detect the WIMP flux with high sensitivity in the low mass region. Both CJPL and CDEX have achieved a remarkable progress in recent two years. The CDEX employs a point-contact germanium semi-conductor detector PCGe whose detection threshold is less than 300 eV. We report the measurement results of Muon flux, monitoring of radioactivity and Radon concentration carried out in CJPL, as well describe the structure and performance of the 1 kg PCGe detector CDEX-1 and 10kg detector array CDEX-10 including the detectors, electronics, shielding and cooling systems. Finally we discuss the physics goals of the CDEX-1, CDEX-10 and the future CDEX-1T detectors.

physics.ins-det↗

arXiv2012

Octahedral Symmetry with Geometrical Breaking: New Prediction for Neutrino Mixing Angle theta_{13} and CP Violation

We propose octahedral group O_h as the family symmetry of neutrino-lepton sector. We find that O_h contains subgroups Z_2(mu-tau) x Z_2(solar) and Z_4^l for realizing the bimaximal (BM) mixings, theta_{23} = theta_{12} = 45^o and theta_{13}=0^o, where Z_2(mu-tau) x Z_2(solar) and Z_4^l serve as the residual symmetries of neutrinos and charged leptons, respectively. We present geometric interpretations of BM mixing in the octahedron, and construct natural geometrical breaking of Z_4^l, leading to nontrivial deviations from the BM mixings. Our theory makes truly simple predictions of a relatively large reactor angle, theta_{13} = 45^o - theta_{12} = 7.5^o - 13.7^o (3 sigma), the nearly maximal atmospheric angle and the approximate maximal Dirac CP violation. These agree well with the current neutrino data, and will be further probed by the on-going and upcoming oscillation experiments.

hep-ph↗