Large Language Models (LLMs) suffer from hallucinations, severely undermining their reliability. While white-box hallucination detection methods that leverage hidden states prevail, they fail to identify and focus on fact-critical information when analyzing token sequences. To address this, we propose LAFaCT, a Localize-then-Analyze detection framework. It first localizes fact-critical tokens using Factual Criticality, a novel metric derived from feature attribution. A subsequent stage then performs a focused sequential analysis on their hidden states. Extensive experiments on eight benchmarks and multiple model families confirm LAFaCT as the new state-of-the-art, with in-depth analyses validating the effectiveness of its core token-localization strategy.

The widespread deployment of Large Language Models (LLMs) has spurred significant progress in the detection of LLM-generated text. However, existing detection methods often rely on statistical features that are insufficient for reliable detection; for example, even though LLM-generated and human-written texts exhibit different probability distributions in surrogate models, they can produce nearly identical entropy values, thereby conflating the two types of text. In this paper, we propose that modulating the decoding temperature and monitoring how the probability distributions respond can better probe the intrinsic discrepancies between two types of text. Building upon this insight, we introduce a new feature termed Temperature Sensitivity (TS) and demonstrate that LLM-generated text tends to exhibit higher TS than human-written text. Finally, we propose NTS, a novel and simple zero-shot detector built upon normalized temperature sensitivity. Extensive experiments across three datasets, multiple domains, and various source models demonstrate the superior effectiveness and robustness of our proposed approach. Code avaliable at: https://github.com/Shixuan-Ma/NTS.

Improving the truthfulness of LLMs to alleviate hallucinations has become critical for promoting the practical deployment of LLMs. Current fine-tuning-based methods ignore the intrinsic discrepancy in the truthfulness correlations across LLM internal modules, and instead treat them equally, which may potentially decrease the performance of truthfulness improvement. In this paper, we propose a truthfulness-driven rank-adaptive LoRA method to improve LLM truthfulness (RaLFiT), which adaptively allocates the ranks in LoRA training according to the truthfulness correlations of modules within LLM. Specifically, it first measures the truthfulness correlation of each LLM module by a probing process, and allocates higher ranks to strongly correlated modules, which means a larger update subspace during training. Experimental results on TruthfulQA show that RaLFiT consistently outperforms previous state-of-the-art methods across the Llama LLM family, verifying its effectiveness and superiority, and for the first time makes the performance of 7B Llama LLMs exceed GPT-4.