[Paper Review] Neutrino-Induced Giant Air Showers in Large Extra Dimension Models

Ambar Jain, Pankaj Jain+2 more|arXiv (Cornell University)|Nov 25, 2000

Astrophysics and Cosmic Phenomena26 references12 citations

TL;DR

This paper investigates neutrino-induced ultra-high-energy (UHE) air showers in large extra dimension models with massive spin-2 exchange, showing that for quantum gravity scale $ M \sim 2-3 $ TeV and neutrino cross sections above 20 mb, shower characteristics—including lateral particle and muon distributions, longitudinal profiles, and shower maximum depth—become indistinguishable from proton-induced showers. The key result is that neutrino-induced showers cannot be ruled out based on current shower morphology alone.

ABSTRACT

In models based on large extra dimensions where massive spin 2 exchange can dominate at high energies, the neutrino-proton cross section can rise to typical hadronic values at energies above 10^20 eV. The neutrino then becomes a candidate for the primary that initiates the highest energy cosmic ray showers. We investigate characteristics of neutrino-induced showers compared to proton-induced showers. The comparison includes study of starting depth, profile with depth, lateral particle distribution at ground and muon lateral distribution at ground level. We find that for cross sections above 20 mb there are regions of parameter space where the two types of showers are essentially indistinguishable. We conclude that the neutrino candidate hypothesis cannot be ruled out on the basis of shower characteristics.

Motivation & Objective

• To assess whether neutrino-induced air showers in large extra dimension models can reproduce the morphological features of observed ultra-high-energy cosmic ray showers.
• To determine if the enhanced neutrino-nucleon cross sections predicted by low-scale gravity models can produce showers indistinguishable from proton-induced showers.
• To evaluate the sensitivity of shower observables—such as lateral particle and muon distributions, longitudinal profiles, and shower maximum depth—to variations in the fundamental scale $ M $ and neutrino energy.
• To test whether existing shower characteristics can rule out neutrinos as the primary particle initiating the highest-energy cosmic ray events.

Proposed method

• Simulated air showers using the AIRES air shower simulation framework for neutrino primaries with energies up to $ 10^{20} $ eV.
• Modeling neutrino-nucleon cross sections via massive spin-2 exchange in large extra dimension scenarios, with cross sections scaling as $ \sigma \sim s^2 $ at high energies.
• Varying the fundamental scale $ M $ from 2 to 7.3 TeV and analyzing shower development across multiple energy regimes.
• Comparing key shower observables—lateral particle and muon distributions, longitudinal profiles, and $ X_{\text{max}} $—between neutrino and proton-induced showers.
• Averaging results over 50 simulated showers to reduce statistical fluctuations and assess robustness of differences.
• Using parameter space scans to identify regions where neutrino and proton showers become indistinguishable in observable features.

Experimental results

Research questions

• RQ1 Can neutrino-induced air showers in large extra dimension models reproduce the lateral particle and muon distributions observed in ultra-high-energy cosmic ray showers?
• RQ2 To what extent do the longitudinal development profiles and shower maximum depths of neutrino showers match those of proton showers for enhanced cross sections?
• RQ3 Are there specific values of the quantum gravity scale $ M $ and neutrino energy where the morphological differences between neutrino- and proton-induced showers vanish?
• RQ4 Can the observed characteristics of super-GZK cosmic ray showers be explained by neutrinos if their cross sections are enhanced to hadronic levels via new physics?
• RQ5 Is the shower maximum depth $ X_{\text{max}} $ a reliable discriminator between neutrino and proton primaries in the presence of large cross sections?

Key findings

• For neutrino-nucleon cross sections above 20 mb, the lateral distributions of charged particles and muons at ground level in neutrino-induced showers closely match those of proton-induced showers in the standard model.
• Longitudinal profiles of charged particles in neutrino showers show minimal differences from proton showers when the quantum gravity scale $ M \approx 2 $ TeV.
• The depth of shower maximum $ X_{\text{max}} $ becomes indistinguishable between neutrino and proton showers for $ M \approx 2 $ TeV, despite a slight shift in average position at higher $ M $.
• When $ M \approx 2.5 $ to $ 3.0 $ TeV, the average $ X_{\text{max}} $ of neutrino showers cannot be brought into alignment with proton shower profiles, indicating a potential discriminant.
• For $ M = 6 $ TeV and $ \beta = 1 $, the cross section reaches 0.3 mb at $ 10^{20} $ eV, while $ M = 6.6 $ TeV or $ M = 7.3 $ TeV with $ \beta = 1 $ or $ \beta = 2 $ reproduces the 0.1 mb value from other models, showing consistency across parameter spaces.
• The study concludes that neutrino-induced showers cannot be ruled out as the origin of ultra-high-energy cosmic ray showers based on morphological characteristics alone, especially in the $ M \sim 2-3 $ TeV range with high cross sections.