arXiv subjects

Diksha Garg

Publications and source records attributed to Diksha Garg.

At least 19 recordsLinked to original sources

arXiv2026

Real-time THz ptychography using an optically modulated aperture

Ptychography allows ordinary cameras to perform both quantitative phase and intensity imaging. However, the requirement for relative object to probe motion and high measurement count significantly limits imaging speed and application scope. In this work, we introduce optically modulated aperture ptychography, using a silicon photomodulator as a rapidly reconfigurable aperture, deployable across the microwave, millimeter wave and terahertz bands. We demonstrate experimentally at ~ 0.1 THz real-time ptychographic image capture, without moving parts. Furthermore, a reconfigurable aperture facilitates diverse and spatially multiplexed probes. We use a multiplexed known-probe reconstruction strategy that improves signal-to-noise ratio and increases the information content per measurement, enabling the capture of fluid dynamics at 16 fps. Our optical modulation approach enables high-throughput ptychographic imaging of dynamic samples, for applications such as non-destructive evaluation and in-vivo biomedical imaging.

physics.optics↗

arXiv2026

A microwave super-resolution imaging approach towards breast cancer margin mapping

Accurate characterisation of margins in excised breast cancer tumours is critical to the success of surgical interventions. Yet margin status is typically confirmed post-operatively using histopathology. Here we present a microwave single pixel imaging technique designed for use in intraoperative margin assessment. By leveraging the photo-induced change in microwave transparency of a silicon modulator placed under the sample, we map the microwave reflectivity of tissue-mimicking phantoms with deeply sub-wavelength resolution, allowing hydration mapping across large areas (10 x 10 cm) at ~1 mm resolution. We evaluate the discriminatory capability of our method using gelatine-based tumour phantoms with water-content variations designed to mimic the contrast between malignant tissue and tumour margins in resected breast specimens. We demonstrate the capability to identify, locate and quantify inadequate margins up to the typically targeted minimum thickness of 2 mm. Furthermore, using numerical modelling, we show that our approach is expected to be resilient to patient-specific tissue differences. These results establish microwave single-pixel imaging as a promising route towards real-time intraoperative assessment of margins in excised breast tumours.

physics.optics↗

arXiv2026

The role of charm and unflavored mesons in prompt atmospheric lepton fluxes

The all-sky very-high-energy ($10^4-10^6$ GeV) atmospheric muon flux measured by IceCube shows a spectral hardening at the highest energies, indicating the presence of a prompt component. IceCube has also measured the atmospheric muon neutrino flux at high energy. However, since this flux is dominated by astrophysical neutrinos, only an upper bound can be placed on the prompt atmospheric $ν_μ+\barν_μ$ contribution. In this work, we provide a new evaluation of the prompt atmospheric muon flux including an intrinsic charm component in the cosmic ray-air interactions. The latter enhances the forward production of $\bar{D}^0$, $D^-$, and $Λ_c$, which subsequently decay into final states containing muons and muon neutrinos. We show how the increase in the prompt muon flux due to intrinsic charm is accompanied by a corresponding enhancement in the prompt muon neutrino flux. We implement different intrinsic charm production models in \texttt{MCEq} to calculate the resulting lepton fluxes. We discuss the challenges of achieving predictions that are simultaneously consistent with both IceCube's high-energy atmospheric muon flux measurements and IceCube upper bounds on the prompt muon neutrino flux, and we quantify the resulting discrepancies. As possible solutions, we explore scaling of the unflavored meson contributions to the prompt atmospheric muon flux to assess how such adjustments can reconcile these differences. The tensions emphasized in our work call for a refinement of the hadronic interaction models, especially the production of unflavored mesons, and for new experimental data sensitive to unflavored meson and heavy flavor production with reliable estimates of the associated uncertainties. We suggest that the energy and zenith angle dependence of muon and neutrino flux ratios from future neutrino telescope measurements may help to disentangle different scenarios.

hep-ph↗

arXiv2025

EUSO-SPB2 Cherenkov Telescope: Overview and First Neutrino Constraints

Earth-skimming tau neutrinos with energies above $\sim 10$ PeV can convert to tau leptons that decay in the atmosphere and initiate upward-going extensive air showers that generate optical Cherenkov signals. On a curtailed NASA balloon flight in May 2023, the Cherenkov telescope (CT) on the Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) was launched and had a short flight at $\sim 30$ km altitude. With some time pointing below the Earth's limb, EUSO-SPB2 CT data allow searches for neutrino events that yield optical flashes from the forward-beamed Cherenkov light. We present an overview of the CT and provide upper limits for the diffuse astrophysical neutrino flux from flight data as a proof-of-principle demonstration. We also briefly describe how the methodology is extended to potential transient neutrino point sources.

astro-ph.HE↗

arXiv2025

Using the Cherenkov Telescope onboard EUSO-SPB2 for Target of Opportunity searches of very high energy neutrino sources

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) mission launched from Wanaka New Zealand on May 13, 2023. The mission ended after 36 h due to a balloon leak that resulted in the payload being lost in the Pacific Ocean. Over the course of the mission, the onboard Cherenkov Telescope (CT) was pointed just below the Earth's limb to search for optical signals from upward-moving extensive air showers that were induced by decaying tau-leptons that were generated by the conversion of $>10$ PeV tau-neutrinos in Earth. Such very-high energy (VHE) neutrinos may be produced in several classes of astrophysical sources that are suspected of possibly accelerating particles to ultra-high energies. In this contribution, we discuss the EUSO-SPB2 Target-of-Opportunity (ToO) campaign to search for VHE neutrino signals coming from astrophysical sources that crossed the CT's field of view ($6.4^\circ \times 12.8^\circ$). We also present a new software tool designed for scheduling observations, the Neutrino Target Scheduler, that we developed to support the ToO campaign. We also calculate upper limits on the neutrino fluences from sources observed during the ToO campaign. Our observations demonstrate the viability of conducting ToO follow-up observations from a near space environment with future balloon missions, such as the pathfinder mission POEMMA-Balloon with Radio.

astro-ph.HE↗

arXiv2025

Atmospheric pion, kaon, and muon fluxes for sub-orbital experiments

Cosmic rays interacting with the Earth's atmosphere generate extensive air showers, which produce Cherenkov, fluorescence and radio emissions. These emissions are key signatures for detection by ground-based, sub-orbital, and satellite-based telescopes aiming to study high energy cosmic ray and neutrino events. However, detectors operating at ground and balloon altitudes are also exposed to a background of atmospheric charged particles, primarily pions, kaons, and muons, that can mimic or obscure the signals from astrophysical sources. In this work, we use coupled cascade equations to calculate the atmospheric pion, kaon and muon fluxes reaching detectors at various altitudes. Our analysis focuses on energies above 10 GeV, where the influence of the Earth's magnetic field on particle trajectories is minimal. We provide angular and energy-resolved flux estimates and discuss their relevance as background for extensive air shower detection. Our results are potentially relevant for interpreting data from current and future balloon-borne experiments such as EUSO-SPB2 and for refining trigger and veto strategies in Cherenkov and fluorescence telescopes.

astro-ph.HE↗

arXiv2025

Prospects for PBR detection of KM3-230213A-like events

POEMMA-Balloon with Radio (PBR) is a scaled-down version of the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) design, optimized to be flown as a payload on one of NASA's sub-orbital super pressure balloons circling the Earth above the southern oceans for a mission duration of more than 20 days. One of the main science objectives of PBR is to follow up astrophysical event alerts in search of neutrinos with very high energy ($10^8 \lesssim E_ν/{\rm GeV} \lesssim 10^{10}$). Of particular interest for anticipated PBR observations, the KM3NeT Collaboration has recently reported the detection of the neutrino KM3-230213A with $10^{7.8} \lesssim E_ν/{\rm GeV} \lesssim 10^{9.0}$. Such an unprecedented event is in tension with upper limits on the cosmic neutrino flux from IceCube and the Pierre Auger Observatory: for a diffuse isotropic neutrino flux there is a $3.5σ$ tension between KM3NeT and IceCube measurements, and about $2.6σ$ if the neutrino flux originates in transient sources. Therefore, if KM3-230213A was not beginner's luck, it becomes compelling to consider beyond Standard Model (BSM) possibilities which could lead to a signal at KM3NeT-ARCA but not at IceCube/Auger. We calculate the PBR horizon-range sensitivity to probe BSM physics compatible with observation at KM3NeT-ARCA and non-observation at IceCube/Auger. As an illustration, we consider a particular class of BSM physics models which has been described in the literature as a possible explanation of KM3-230213A.

astro-ph.HE↗

arXiv2025

Prompt atmospheric leptons and the potential role of intrinsic charm

The all-sky very-high energy ($10^4-10^6$ GeV) atmospheric muon flux is most recently measured by IceCube, where in the higher energy range, the spectrum hardens indicating a prompt component. IceCube also measures the atmospheric muon neutrino flux at high energy. Since this is dominated by the astrophysical flux, they are only able to set an upper bound on the prompt atmospheric muon neutrino flux contribution. We provide a new evaluation of the prompt atmospheric muon flux including for the first time an intrinsic charm component to colliding nucleons. This increases forward production of $\bar{D}^{0}$, $D^-$ and $Λ_c$ which decay into final states that can contain muons and muon neutrinos. We show how the increase in the prompt muon flux due to intrinsic charm has an associated increase in the prompt muon neutrino flux. We consider the Regge ansatz for intrinsic charm production that we implement in MCEq used for the calculation of the lepton fluxes. We discuss the challenges of obtaining predictions that are simultaneously consistent with both IceCube's high energy atmospheric muon flux measurements and their upper bound on the prompt muon neutrino flux. We quantify the discrepancies.

hep-ph↗

arXiv2025

A generalization of Rao's theorem to graded $R$-subalgebras of $R[t]$

Let $R$ be a Noetherian local ring of Krull dimension $d$ such that $(d!)R = R$, and let $A$ be a graded $R$-subalgebra of the polynomial algebra $R[t]$. We prove that every unimodular row of length $d + 1$ over $A$ can be completed to an invertible matrix. This is a generalization of a classical result by Rao, who proved that in the same setting, every unimodular row of length $d + 1$ over $R[t]$ admits a completion to an invertible matrix.

math.AC↗

arXiv2025

On Projective modules over graded $R$-subalgebras of $R[X,1/X]$

Let $R$ be a Noetherian ring of dimension $d$ and $A$ be a graded $R$-subalgebra of $R[X,1/X]$. Let $P$ be a projective module over $A$ of rank $r \geq \max\{d+1,2\}$ and $\v=(a,p)$ be a unimodular element of $A \oplus P$. We find an elementary automorphism $τ$ such that $τ(\v) = (1, 0)$. Consequently, we obtain the cancellative property of $P$. We show that $P$ splits off a free summand of rank one. When $A = R[X]$ or $R[X, 1/ X]$, the results are well-known due to the contributions by various authors.

math.AC↗

arXiv2025

The Extreme Universe Observatory on a Super-Pressure Balloon II: Mission, Payload, and Flight

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) is a pathfinder mission toward a space-based observatory such as the Probe of Extreme Multi-Messenger Astrophysics (POEMMA). The aim of POEMMA is the observation of Ultra High Energy COsmic Rays (UHECRs) in order to elucidate their nature and origins and to discover $\gtrsim$ 20 PeV very high energy neutrinos that originate from transient and steady astrophysical sources. EUSO-SPB2 was launched from Wānaka New Zealand on May 13th, 2023 as a NASA Balloon Program Office test flight. The mission goals included making the first near-space altitude observations of the fluorescence emission from UHECR-induced extensive air showers (EASs) and making the first direct Cherenkov light emission from PeV cosmic rays traversing Earth's atmosphere. In addition, a Target of Opportunity program was developed for selecting and scheduling observations of potential neutrino sources as they passed just below the Earth's limb. Although a leaky balloon forced termination over the Pacific Ocean after 37 hours, data was collected to demonstrate the successful commissioning and operation of the instruments. This paper includes a description of the payload and the key instruments, pre-flight instrument characterizations in the lab and in the desert, flight operations and examples of the data collected. The flight was too short to catch a UHECR event via fluorescence, however about 10 candidate EAS events from cosmic rays were recorded via Cherenkov light.

astro-ph.HE↗

arXiv2024

The EUSO-SPB2 Fluorescence Telescope for the Detection of Ultra-High Energy Cosmic Rays

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) flew on May 13$^{\text{th}}$ and 14$^{\text{th}}$ of 2023. Consisting of two novel optical telescopes, the payload utilized next-generation instrumentation for the observations of extensive air showers from near space. One instrument, the fluorescence telescope (FT) searched for Ultra-High Energy Cosmic Rays (UHECRs) by recording the atmosphere below the balloon in the near-UV with a 1~$μ$s time resolution using 108 multi-anode photomultiplier tubes with a total of 6,912 channels. Validated by pre-flight measurements during a field campaign, the energy threshold was estimated around 2~EeV with an expected event rate of approximately 1 event per 10 hours of observation. Based on the limited time afloat, the expected number of UHECR observations throughout the flight is between 0 and 2. Consistent with this expectation, no UHECR candidate events have been found. The majority of events appear to be detector artifacts that were not rejected properly due to a shortened commissioning phase. Despite the earlier-than-expected termination of the flight, data were recorded which provide insights into the detectors stability in the near-space environment as well as the diffuse ultraviolet emissivity of the atmosphere, both of which are impactful to future experiments.

astro-ph.IM↗

arXiv2023

Atmospheric muon fluxes at sub-orbital neutrino detectors

Very-high-energy and ultra-high-energy neutrinos are messengers of energetic sources in the universe. Sub-orbital and satellite-based neutrino telescopes employ detectors of the atmospheric Cherenkov emission from extensive air showers (EASs) generated by charged particles. These Cherenkov detectors can be pointed below or above the Earth's limb. Cherenkov emissions produced from directions below the limb are from upward-going EASs produced in the atmosphere sourced by Earth-skimming neutrinos. When the Cherenkov telescope is pointed slightly above the Earth's limb, signals from EASs are initiated by cosmic ray interactions in the atmosphere. For sub-orbital detectors, muons produced from cosmic rays in the atmosphere can directly hit the Cherenkov telescope. Using a semi-analytic technique with cascade equations for atmospheric particle fluxes, we quantify the atmospheric muon flux that reaches sub-orbital telescopes like Extreme Universe Space Observatory Super Pressure Balloon 2 (EUSO-SPB2). We assess this potential background to the EAS signals. The calculation technique may also provide an understanding of the evolution of the muon content in individual EAS.

astro-ph.HE↗

arXiv2023

Neutrino propagation through Earth: modeling uncertainties using nuPyProp

Using the Earth as a neutrino converter, tau neutrino fluxes from astrophysical point sources can be detected by tau-lepton-induced extensive air showers (EASs). Both muon neutrino and tau neutrino induced upward-going EAS signals can be detected by terrestrial, sub-orbital and satellite-based instruments. The sensitivity of these neutrino telescopes can be evaluated with the nuSpaceSim package, which includes the nuPyProp simulation package. The nuPyProp package propagates neutrinos ($ν_μ$, $ν_τ$) through the Earth to produce the corresponding charged leptons (muons and tau-leptons). We use nuPyProp to quantify the uncertainties from Earth density models, tau depolarization effects and photo-nuclear electromagnetic energy loss models in the charged lepton exit probabilities and their spectra. The largest uncertainties come from electromagnetic energy loss modeling, with as much as a 20-50% difference between the models. We compare nuPyProp results with other simulation package results.

hep-ph↗

arXiv2023

Probing Quantum Gravity with Elastic Interactions of Ultra-High-Energy Neutrinos

The next generation of radio telescopes will be sensitive to low-scale quantum gravity by measuring ultra-high-energy neutrinos. In this letter, we demonstrate for the first time that neutrino-nucleon soft interactions induced by TeV-scale gravity would significantly increase the number of events detected by the IceCube-Gen2 radio array in the EeV regime. However, we show that these experiments cannot measure the total cross section using only the angular and energy information of the neutrino flux, unless assumptions on the underlying inelasticity distribution of neutral interactions are made.

hep-ph↗

arXiv2023

Neutrino propagation in the Earth and emerging charged leptons with $\texttt{nuPyProp}$

Ultra-high-energy neutrinos serve as messengers of some of the highest energy astrophysical environments. Given that neutrinos are neutral and only interact via weak interactions, neutrinos can emerge from sources, traverse astronomical distances, and point back to their origins. Their weak interactions require large target volumes for neutrino detection. Using the Earth as a neutrino converter, terrestrial, sub-orbital, and satellite-based instruments are able to detect signals of neutrino-induced extensive air showers. In this paper, we describe the software code $\texttt{nuPyProp}$ that simulates tau neutrino and muon neutrino interactions in the Earth and predicts the spectrum of the $τ$-lepton and muons that emerge. The $\texttt{nuPyProp}$ outputs are lookup tables of charged lepton exit probabilities and energies that can be used directly or as inputs to the $\texttt{nuSpaceSim}$ code designed to simulate optical and radio signals from extensive air showers induced by the emerging charged leptons. We describe the inputs to the code, demonstrate its flexibility and show selected results for $τ$-lepton and muon exit probabilities and energy distributions. The $\texttt{nuPyProp}$ code is open source, available on Github.

astro-ph.HE↗

arXiv2022

Tau depolarization at very high energies for neutrino telescopes

The neutrino interaction length scales with energy, and becomes comparable to Earth's diameter above 10's of TeV energies. Over terrestrial distances, the tau's short lifetime leads to an energetic regenerated tau neutrino flux, tau neutrino to tau to tau neutrino, within the Earth. The next generation of neutrino experiments aim to detect ultra-high energy neutrinos. Many of them rely on detecting either the regenerated tau neutrino, or a tau decay shower. Both of these signatures can be affected by the polarization of the tau through the energy distribution of the secondary particles produced from the tau's decay. While taus produced in weak interactions are nearly 100 percent polarized, it is expected that taus experience some depolarization due to electromagnetic interactions in the Earth. In this paper, for the first time we quantify the depolarization of taus in electromagnetic energy loss. We find that tau depolarization has only small effects on the final energy of tau neutrinos or taus produced by high energy tau neutrinos incident on the Earth. Tau depolarization can be directly implemented in Monte Carlo simulations such as nuPyProp and TauRunner.

hep-ph↗

arXiv2022

Learning to Liquidate Forex: Optimal Stopping via Adaptive Top-K Regression

We consider learning a trading agent acting on behalf of the treasury of a firm earning revenue in a foreign currency (FC) and incurring expenses in the home currency (HC). The goal of the agent is to maximize the expected HC at the end of the trading episode by deciding to hold or sell the FC at each time step in the trading episode. We pose this as an optimization problem, and consider a broad spectrum of approaches with the learning component ranging from supervised to imitation to reinforcement learning. We observe that most of the approaches considered struggle to improve upon simple heuristic baselines. We identify two key aspects of the problem that render standard solutions ineffective - i) while good forecasts of future FX rates can be highly effective in guiding good decisions, forecasting FX rates is difficult, and erroneous estimates tend to degrade the performance of trading agents instead of improving it, ii) the inherent non-stationary nature of FX rates renders a fixed decision-threshold highly ineffective. To address these problems, we propose a novel supervised learning approach that learns to forecast the top-K future FX rates instead of forecasting all the future FX rates, and bases the hold-versus-sell decision on the forecasts (e.g. hold if future FX rate is higher than current FX rate, sell otherwise). Furthermore, to handle the non-stationarity in the FX rates data which poses challenges to the i.i.d. assumption in supervised learning methods, we propose to adaptively learn decision-thresholds based on recent historical episodes. Through extensive empirical evaluation, we show that our approach is the only approach which is able to consistently improve upon a simple heuristic baseline. Further experiments show the inefficacy of state-of-the-art statistical and deep-learning-based forecasting methods as they degrade the performance of the trading agent.

cs.LG↗