arXiv subjects

T. D. Le

Publications and source records attributed to T. D. Le.

4 recordsLinked to original sources

arXiv2026

Probing Variations of Newton's Constant in Strong Gravitational Fields

The constancy of Newton's gravitational constant G is a fundamental prediction underlying general relativity and a critical assumption in theories of gravity beyond it. We report a high-precision test of a possible temporal variation of G in a strong gravitational field, using high-resolution ultraviolet spectra of Ni V absorption lines in the white dwarf G191-B2B obtained with the Hubble Space Telescope Imaging Spectrograph (HST/STIS). By comparing the measured line centroids with laboratory wavelengths and isolating the gravitational-redshift contribution, we obtain dG/G = (-0.014 +/- 0.016) x 10^-15 yr^-1 at a strong-field potential phi approximately 10^4, corresponding to an absorption redshift z_abs approximately 8.47 x 10^-5. The result is consistent with a constant G and places a stringent constraint on its secular variation in the strong-field regime. Our measurement demonstrates the potential of white-dwarf stars as a sensitive probe of temporal variations in the gravitational coupling.

gr-qc↗

arXiv2025

Calibration of a $Δ$E-E telescope based on CeBr$_3$ scintillator for secondary charged particles measurements in hadron therapy

Hadrontherapy is an established cancer treatment method that enables a more localized dose deposition compared to conventional radiotherapy, potentially reducing the dose to surrounding healthy tissues in certain clinical cases. However, a key limitation in current treatment planning lies in the limited experimental data available for the characterization of secondary particles generated by nuclear interactions of the primary beam with tissues, which directly impacts the accuracy of Monte Carlo tools and analytical models used in dose calculations. Indeed, this leads to the adoption of larger safety margins and can limit the use of hadrontherapy for treating certain complex or sensitive tumor locations. This work is part of the context of the characterization of secondary charged particles generated by ion beams in the energy range relevant for particle therapy applications, using a $ΔE-E$ telescope comprising a CeBr$_3$ crystal scintillator and a plastic scintillator. The calibration and response of this telescope to ions commonly used in clinical settings is presented in this work, highlighting adherence to Birks' law for accurate energy measurements. This study is the first to optimize a $ΔE-E$ telescope combining CeBr$_3$ and plastic scintillators specifically for secondary particle detection in hadrontherapy. It represents an essential step toward the experimental acquisition of nuclear data, enabling accurate measurement and identification of secondary charged particles generated by therapeutic beams in tissue-equivalent materials. The system is designed for use in controlled experimental setups that reproduce clinical conditions, with the goal of improving the predictive accuracy of treatment planning software through enhanced Monte Carlo simulation inputs.

physics.ins-det↗

arXiv2024

Searching for cosmological variation of the proton-to-electron mass ratio using a single $H_2$ system

Exploring physics beyond General Relativity and the Standard Model of Particle Physics involves investigating spacetime variations in natural constants. This study employs an $H_2$-single of QSO 0347-383 observational spectrum to propose a unique approach for detecting potential changes in the proton-to-electron mass ratio. By comparing the ratio from observational and laboratory data in the Lyman-Alpha transition line, we derive a cosmological variation of $Δμ/ μ= (0.120 \pm 0.144) \times 10^{-8}$ at $z_{abs}=3.025$. This approach not only advances fundamental physics understanding but also introduces innovative techniques for analyzing high-redshift QSO systems.

astro-ph.CO↗

arXiv2020

Answering Mermin's Challenge with Conservation per No Preferred Reference Frame

In 1981, Mermin published a now famous paper titled, "Bringing home the atomic world: Quantum mysteries for anybody" that Feynman called, "One of the most beautiful papers in physics that I know." Therein, he presented the "Mermin device" that illustrates the conundrum of quantum entanglement per the Bell spin states for the "general reader." He then challenged the "physicist reader" to explain the way the device works "in terms meaningful to a general reader struggling with the dilemma raised by the device." Herein, we show how "conservation per no preferred reference frame (NPRF)" answers that challenge. In short, the explicit conservation that obtains for Alice and Bob's Stern-Gerlach spin measurement outcomes in the same reference frame holds only on average in different reference frames, not on a trial-by-trial basis. This conservation is SO(3) invariant in the relevant symmetry plane in real space per the SU(2) invariance of its corresponding Bell spin state in Hilbert space. Since NPRF is also responsible for the postulates of special relativity, and therefore its counterintuitive aspects of time dilation and length contraction, we see that the symmetry group relating non-relativistic quantum mechanics and special relativity via their "mysteries" is the restricted Lorentz group.

quant-ph↗