Testing beyond the Standard Model scenarios in next-generation long-baseline neutrino oscillation experiments

Abstract

In this thesis, we assess the sensitivity of next-generation long-baseline neutrino oscillation experiments, DUNE, T2HK, and T2HKK, to three popular beyond the Standard Model (BSM) scenarios. Within the three BSM studies, we examine: (i) long-range neutrino-matter interactions induced by flavor-dependent, anomaly-free gauged baryon-lepton symmetries mediated by ultra-light vector boson, showing that DUNE and T2HK can constrain, discover, and in some favorable cases distinguish among different symmetries; (ii) Lorentz invariance violation (LIV), where we derive analytical dependencies of CPT-conserving and CPT-violating LIV parameters on baseline and energy, highlighting the superior reach of DUNE in probing all the LIV parameters, in contrast to T2HK, which is essentially blind to the CPT-conserving LIV parameters; and (iii) active-sterile oscillations over a broad range of $Δm^2_{41}$, where we derive sensitivity to CP phases for benchmark choices of $Δm^2_{41}$ and establish exclusion limits, emphasizing the role of near detectors. Together, these studies show that future long-baseline facilities not only resolve the neutrino mass ordering, value of $δ_{\rm CP}$, and $θ_{23}$ octant, but also provide powerful probes of BSM physics.

Figures (49)

• Figure 1.1: Neutrino (left panel) and antineutrino (right panel) charged-current cross sections across different energies. These figures are taken from Ref. nuSTORM:2012jbd.
• Figure 2.1: Feynman diagrams of the neutrino interactions with the ordinary matter. Diagram (a) represents the NC interaction mediated by the neutral $Z^0$ vector boson. Diagram (b) represents the CC interaction mediated by the $W^\pm$ vector boson.
• Figure 3.1: Overview of projected constraints and discovery prospects of long-range neutrino interactions achieved by combining DUNE and T2HK. Results are on the effective coupling of the new gauge boson, $Z^\prime$, that mediates the interaction, across all the candidate $U(1)^\prime$ symmetries that we consider could induce long-range interactions (table \ref{['tab:charges']}), and for 10 years of operation of each experiment. For this figure, we assume that the true neutrino mass ordering is normal. Existing limits are from a recent global oscillation fit Coloma:2020gfv, shown also across all symmetries, and, for specific symmetries, from atmospheric neutrinos Joshipura:2003jh, solar and reactor neutrinos Bandyopadhyay:2006uh, and non-standard interactions Super-Kamiokande:2011damOhlsson:2012kfGonzalez-Garcia:2013usa. The estimated sensitivity from present flavor-composition measurements of high-energy astrophysical neutrinos in IceCube is from Ref. Agarwalla:2023sng. Indirect limits Wise:2018rnb are from black-hole superradiance Baryakhtar:2017ngi, the early Universe Dror:2020fbh, compact binaries KumarPoddar:2019ceq, and the weak gravity conjecture Arkani-Hamed:2006emk, assuming a lightest neutrino mass of $0.01$ eV. See sections \ref{['sec:intro']}, \ref{['sec:constraints_pot']}, and \ref{['sec:discovery']} for details. DUNE and T2HK may constrain long-range interactions more strongly than ever before, or discover them, regardless of which $U(1)^\prime$ symmetry is responsible for inducing them.
• Figure 3.2: Feynman diagrams of the new neutrino-matter interactions that we consider. The interaction Lagrangian is eq. (\ref{['equ:full_lagrangian']}). Diagram (a) represents the new interaction mediated by a new $Z^\prime$ neutral vector boson, with coupling constant $g_{Z^\prime}$. Diagram (b) represents the mixing between $Z$ and $Z^\prime$. In our analysis, we account for the contribution of diagram (a) for all $U(1)^\prime$ symmetries except for $L_\mu-L_\tau$, for which diagram (a) is replaced by diagram (b). See section \ref{['sec:formalism_lagrangians']} for details.
• Figure 3.3: Oscillation probabilities (top) and event distributions (bottom) in the presence of a new matter potential in DUNE. In this figure, we show examples computed assuming a matter potential matrix of the form $\mathbf{V}_{\rm LRI} = \textrm{diag}(0,0,-V_{\rm LRI})$, with varying value of $V_{\rm LRI}$, as would be induced by the $B - 3L_\tau$ and $L - 3L_\tau$ symmetries (table \ref{['tab:charges']}). Top left:$\hbox{$\nu_{\mu}$} \to \hbox{$\nu_e$}$ probability as a function of the neutrino energy, $E$, and new matter potential, $V_{\rm LRI}$. Top right: Oscillation probability computed for choices A--D of the potential, showing the change in amplitude and phase compared to standard oscillations. Bottom left: Total number, i.e., signal plus background, of $\hbox{$\nu_{\mu}$}\to\hbox{$\nu_e$}$ appearance events after 10 years of run-time (5 yr in $\nu$ and $\bar{\nu}$ modes each), as a function of reconstructed neutrino energy, $E_{\rm rec}$, and $V_{\rm LRI}$. Bottom right: Event spectra computed for choices A--D of the potential. See section \ref{['sec:formalism']} for details and fig. \ref{['fig:t2hk_prob_events']} for analogous results for T2HK. In DUNE, resonant effects may appear if the new matter potential $V_{\rm LRI} \approx 10^{-13}$--$10^{-12}$ eV.