arXiv subjects

Yoram Rozen

Publications and source records attributed to Yoram Rozen.

7 recordsLinked to original sources

arXiv2025

Radiometric Interferometry for Deep Space Navigation using Geostationary Satellites

Deep space navigation presents significant challenges due to the unavailability of Global Navigation Satellite System (GNSS) signals and severe signal attenuation over interplanetary distances. Traditional terrestrial systems, such as NASA Deep Space Network (DSN) and ESA ESTRACK, rely on Very Long Baseline Interferometry (VLBI) for angular positioning. However, these systems are limited by relatively short baselines, atmospheric distortions requiring extensive calibration, and reduced visibility availability due to Earth rotation. This research proposes a complementary deep space navigation approach using space based interferometry, in which radio signals from the spacecraft are received and cross correlated onboard Geostationary Earth Orbit (GEO) satellites. By replacing terrestrial VLBI stations with dual GEO platforms, the method significantly extends the effective baseline, removes atmospheric phase errors, and provides almost continuous visibility to deep space targets. Unlike Earth based systems, GEO based interferometry maintains persistent station mutual visibility, enabling higher measurement availability and more flexible mission support. A complete system model is presented, including the principles of dual frequency phase based angular tracking and a structured error budget analysis. Theoretical results show that the GEO based system achieves a total angular error of approximately 3.73 nanoradians, within the same order of magnitude as terrestrial VLBI. Space based architecture nearly doubles the geometrical availability for interferometric tracking, while eliminating atmospheric distortions. These findings support the feasibility of the GEO based VLBI concept and motivate continued research and field validation for future deep space navigation applications.

astro-ph.IM↗

arXiv2020

Searching for New Physics with $b\bar{b} \ell^+ \ell^-$ Contact Interactions

We study the impact of contact interactions involving two leptons (electrons or muons) and two $b$-quarks ($b \bar{b} \ell^+ \ell^-$) on the high-mass di-lepton region at the LHC. We consider different selections of $b$-tagged jet multiplicities in the di-lepton final states: inclusive (no selection), 0, 1 and 2 $b$-tagged jets, and show that the single $b$-jet selection significantly improves the sensitivity to New Physics (NP) in the form of the $b \bar{b} \ell^+ \ell^-$ contact term. We obtain a better sensitivity compared to the currently existing searches of NP in the di-lepton inclusive channel. In particular, the expected limits go beyond competitive bounds set by LEP (for electrons) on the scale of NP, $Λ$, by a factor of $1.2-3.1$, depending on the chirality structure of the operator. In addition, the expected limits on $Λ$, set by using a non-resonant LHC di-lepton inclusive search, are expected to be improved by a factor of $1.3-1.4$ for both electrons and muons.

hep-ex↗

arXiv2019

Searching for Dark Matter with $t\overline{t}$ Resonance

Many models containing particles which are candidates for dark matter, assume the standard model particles and the dark matter candidates are mediated by a spin-0 particle. At the LHC, one can use these models for dark matter searches. One of the possible approaches for the search of these models is by considering the decay of the spin-0 particle to a pair of $t\bar{t}$, thus modifying the pattern of the top quark pair invariant mass spectrum. This search suggests a good sensitivity in a parameter space different than the more traditional searches. We examine this sensitivity and put limits on two benchmark models containing candidates for dark matter, using previous ATLAS results. It was found that when the mediator mass ($m_{Y_0}$) and the dark matter candidate mass ($m_χ$) have values of $m_{Y_0} \sim 2 \cdot m_χ$, mediator masses in the range of $[400,600]$ GeV are excluded. We compare our results to direct detection experiments and show that we gain sensitivity for new regions which are not covered by other searches.

hep-ex↗

arXiv2018

LHC Dark Matter Working Group: Next-generation spin-0 dark matter models

Dark matter (DM) simplified models are by now commonly used by the ATLAS and CMS Collaborations to interpret searches for missing transverse energy ($E_T^\mathrm{miss}$). The coherent use of these models sharpened the LHC DM search program, especially in the presentation of its results and their comparison to DM direct-detection (DD) and indirect-detection (ID) experiments. However, the community has been aware of the limitations of the DM simplified models, in particular the lack of theoretical consistency of some of them and their restricted phenomenology leading to the relevance of only a small subset of $E_T^\mathrm{miss}$ signatures. This document from the LHC Dark Matter Working Group identifies an example of a next-generation DM model, called $\textrm{2HDM+a}$, that provides the simplest theoretically consistent extension of the DM pseudoscalar simplified model. A comprehensive study of the phenomenology of the $\textrm{2HDM+a}$ model is presented, including a discussion of the rich and intricate pattern of mono-$X$ signatures and the relevance of other DM as well as non-DM experiments. Based on our discussions, a set of recommended scans are proposed to explore the parameter space of the $\textrm{2HDM+a}$ model through LHC searches. The exclusion limits obtained from the proposed scans can be consistently compared to the constraints on the $\textrm{2HDM+a}$ model that derive from DD, ID and the DM relic density.

hep-ex↗

arXiv2018

DM+$b\bar b$ simulations with DMSimp: an update

Searches for dark matter (DM) produced using collider data probe wide regions of the allowed parameter space of many models and have become competitive with more traditional searches. The interpretations of the results can be efficiently performed in simplified models, which feature only a mediator and a DM candidate together with the interactions among them and the standard model particles. The DMSimp model in FeynRules currently features a wide set of $s$-channel simplified models and can be exploited by the MadGraph5_aMC@NLO framework to produce event samples including NLO QCD corrections for realistic simulations. Higher-order corrections typically have a sizeable impact on the total production rate and lead to a reduction of the theoretical uncertainties. In this short note we report on a recent update of the DMSimp model, which makes it possible to simulate dark matter production in association with bottom quarks in a mixed four-flavour scheme, where the $\overline{\rm MS}$ renormalisation for the bottom-quark Yukawa is employed, while the bottom quark mass is on shell. By comparing with five-flavour scheme, we show that the mixed four-flavor scheme provides reliable predictions for DM+$b\bar b$ final states in a wide range of DM masses.

hep-ex↗

arXiv2018

Establishing a Search for $b \rightarrow s \ell^{+} \ell^{-}$ Anomalies at the LHC

One of the fundamental predictions of the Standard Model is Lepton Flavour Universality. Any deviation from this prediction would indicate the existence of physics beyond the Standard Model. Recent LHCb measurements present a pattern of deviations from this prediction in rare B-meson decays. While not yet statistically significant (currently $2.2-2.6 σ$), these measurements show an imbalance in the ratio of B-meson decays to a pair of muons in association with a Kaon and decays to a pair of electrons in association with a Kaon. If the measured deviations are indeed present in nature, new physics may mediate interactions involving a pair of same flavour leptons, a $b$- and an $s$-quark. We present the prospect for a search of new physics in this type of interactions at the LHC, in a process that involves an $s$-quark, and a final state with two leptons and a $b$-jet. The proposed search can improve the sensitivity to new physics in these processes by a factor of four compared to current searches with in the total dataset expected at the LHC.

hep-ph↗

arXiv2007

Hiding the Higgs at the LHC

We study a simple extension of the standard model where scalar singlets that mix with the Higgs doublet are added. This modification to the standard model could have a significant impact on Higgs searches at the LHC. The Higgs doublet is not a mass eigenstate and therefore the expected nice peak of the standard model Higgs disappears. We analyze this scenario finding the required properties of the singlets in order to make the Higgs "invisible" at the LHC. In some part of the parameter space even one singlet could make the discovery of the SM Higgs problematic. In other parts, the Higgs can be discovered even in the presence of many singlets.

hep-ph↗