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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 613 records · Page 34
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DOE OSTI2017

Strongly coupled dark energy with warm dark matter vs. LCDM

Cosmologies including strongly Coupled (SC) Dark Energy (DE) and Warm dark matter (SCDEW) are based on a conformally invariant (CI) attractor solution modifying the early radiative expansion. Then, aside of radiation, a kinetic field Φ and a DM component account for a stationary fraction, ∼ 1 %, of the total energy. Most SCDEW predictions are hardly distinguishable from LCDM, while SCDEW alleviates quite a few LCDM conceptual problems, as well as its difficulties to meet data below the average galaxy scale. The CI expansion begins at the end of inflation, when Φ (future DE) possibly plays a role in reheating, and ends at the Higgs scale. Afterwards, a number of viable options is open, allowing for the transition from the CI expansion to the present Universe. In this paper: (i) We show how the attractor is recovered when the spin degrees of freedom decreases. (ii) We perform a detailed comparison of CMB anisotropy and polarization spectra for SCDEW and LCDM, including tensor components, finding negligible discrepancies. (iii) Linear spectra exhibit a greater parameter dependence at large k 's, but are still consistent with data for suitable parameter choices. (iv) We also compare previous simulation results with fresh data on galaxy concentration. Finally, (v) we outline numerical difficulties at high k . This motivates a second related paper [1], where such problems are treated in a quantitative way.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Stellar limits on light CP-even scalar

Abstract We revisit the astrophysical constraints on a generic light CP-even scalar particle S , mixing with the Standard Model (SM) Higgs boson, from observed luminosities of the Sun, red giants, white dwarfs and horizontal-branch stars. The production of S in the stellar core is dominated by the electron-nuclei bremsstrahlung process e + N → e + N + S . With the S decay and reabsorption processes taken into consideration, we find that the stellar luminosity limits exclude a broad range of parameter space in the S mass-mixing plane, with the scalar mass up to 350 keV and the mixing angle ranging from 7.0 × 10 -18 to 3.4 × 10 -3 . We also apply the stellar limits to a real-singlet scalar extension of the SM, where we can relate the mixing angle to the parameters in the scalar potential. In both the generic scalar case and the real-singlet extension, we show that the stellar limits preclude the scalar interpretation of the recently observed XENON1T excess in terms of the S particles emitted from the Sun.

Astronomy & Astrophysics↗
DOE OSTI2022

Improved stellar limits on a light CP-even scalar

We derive improved stellar luminosity limits on a generic light CP-even scalar field S mixing with the Standard Model (SM) Higgs boson from the supernova SN1987A, the Sun, red giants (RGs) and white dwarfs (WDs). For the first time, we include the geometric effects for the decay and absorption of S particles in the stellar interior. For SN1987A and the Sun, we also take into account the detailed stellar profiles. We find that a broad range of the scalar mass and mixing angle can be excluded by our updated astrophysical constraints. For instance, SN1987A excludes 1.0 × 10 -7 ≲ sinθ ≲ 3.0 × 10 -5 and scalar mass up to 219 MeV, which covers the cosmological blind spot with a high reheating temperature. The updated solar limit excludes the mixing angle in the range of 1.5 × 10 -12 < sinθ < 1, with scalar mass up to 45 keV. The RG and WD limits are updated to 5.3 × 10-13 < sinθ < 0.39 and 2.8 × 10 -18 < sinθ < 1.8 × 10 -4 , with scalar mass up to 392 keV and 290 keV, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Primordial black holes from bubble collisions during a first-order phase transition

We study the possibility of production of primordial black holes (PBHs) from bubble collisions during a first-order phase transition. While typical colliding bubbles are small and irrelevant for PBH production, we find that those that can produce PBHs must have a macroscopically thick fluid shell and have been born much before the typical nucleation time. Particularly large uncertainties arise from an exponential sensitivity of the nucleation rate on the required duration of bubble growth which depends on the details of the collisions and the evolution of the spacetime metric toward the end of the phase transition. We introduce a few parameters to be obtained from future numerical simulation to represent those unknowns, and estimate the PBH abundance in an Abelian Higgs benchmark model and show that it can be significant. We predict an approximately monochromatic PBH mass spectrum, and find regions in the parameter space where the PBHs can constitute entire dark matter or even overclose the Universe. Our result thus shows that models with a first-order phase transition can be constrained by overabundant PBHs or null results of other PBH searches. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Proton decay prediction from a gauge-Higgs unification scenario in five dimensions

The Higgs boson mass and top quark mass imply that the Higgs quartic coupling vanishes around the scale of 10 9 -10 13 GeV, depending on the precise value of the top quark mass. The vanishing quartic coupling can be naturally addressed if the Higgs field originates from a 5-dimensional gauge field and the 5th dimension is compactified at the scale of the vanishing Higgs quartic coupling, which is a scenario based on gauge-Higgs unification. We present a general prediction of the scenario on the proton decay process p→π 0 e + . In many gauge-Higgs unification models, the 1st generation fermions are localized towards an orbifold fixed point in order to realize the realistic Yukawa couplings. Hence, four-fermion operators responsible for the proton decay can appear with a suppression of the 5-dimensional Planck scale (not the 4-dimensional Planck scale). Since the 5-dimensional Planck scale is connected to the compactification scale, we have a correlation between the proton partial decay width and the top quark mass. We show that the future Hyper-Kamiokande experiment may discover the proton decay if the top quark pole mass is larger than about 172.5 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Search for a Charged Higgs Boson Produced in the Vector-Boson Fusion Mode with Decay H ± → W ± Z using p p Collisions at s = 8 TeV with the ATLAS Experiment

A search for a charged Higgs boson, H ± , decaying to a W ± boson and a Z boson is presented. The search is based on 20.3 fb⁻¹ of proton-proton collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. The H ± boson is assumed to be produced via vector-boson fusion and the decays W ± →qq'¯ and Z→e⁺e⁻/μ⁺μ⁻ are considered. The search is performed in a range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the production of an H ± boson is observed. Upper limits of 31–1020 fb at 95% C.L. are placed on the cross section for vector-boson fusion production of an H ± boson times its branching fraction to W ± Z. The limits are compared with predictions from the Georgi-Machacek Higgs triplet model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

What tells gravity on the shape and size of an electron

Gravitational field of an electron, fixed by experimental values of its mass, spin, charge and magnetic moment, is given by the metric of Kerr-Newman (KN) solution. Unexpectedly, this metric contains a singular ring of the Compton radius, which should be regulated resulting in a weeak and smooth source. The consistent source takes the form of an oblate vacuum bubble, bounded by a closed string of the Compton radius. The bubble turns out to be relativistically rotating and should be filled by a coherently oscillating Higgs field in a false vacuum state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

The Lightest Neutralino Annihilation in NMSSM with CP Violation

We discuss the violation of CP invariance in the Higgs sector and its impact on the physical characteristics of the neutralino, and its implication in the processes of annihilation. The process of pair annihilation of the lightest neutralinos into two photons for NMSSM in the one-loop approximation considering the violation of CP-invariance in the extended scalar Higgs sector is calculated. The analysis of the obtained results and the comparison are given.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Updated search for long-lived particles decaying to jet pairs

A search is presented for long-lived particles with a mass between 25 and 50GeV/c 2 and a lifetime between 2 and 500 ps, using proton–proton collision data corresponding to an integrated luminosity of 2.0fb -1 , collected by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The particles are assumed to be pair-produced in the decay of a 125GeV/c 2 Standard-Model-like Higgs boson. The experimental signature is a single long-lived particle, identified by a displaced vertex with two associated jets. No excess above background is observed and limits are set on the production cross-section as a function of the mass and lifetime of the long-lived particle.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Search for a heavy pseudoscalar boson decaying to a Z and a Higgs boson at $\sqrt{s}=13\,\text {Te}\text {V}$

A search is presented for a heavy pseudoscalar boson $\text {A}$ decaying to a Z boson and a Higgs boson with mass of 125 $\,\text {GeV}$ . In the final state considered, the Higgs boson decays to a bottom quark and antiquark, and the Z boson decays either into a pair of electrons, muons, or neutrinos. The analysis is performed using a data sample corresponding to an integrated luminosity of 35.9 $\,\text {fb}^{-1}$ collected in 2016 by the CMS experiment at the LHC from proton–proton collisions at a center-of-mass energy of 13 $\,\text {Te}\text {V}$ . The data are found to be consistent with the background expectations. Exclusion limits are set in the context of two-Higgs-doublet models in the $\text {A}$ boson mass range between 225 and 1000 $\,\text {GeV}$ .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for long-lived particles decaying to e± μ∓ ν

Long-lived particles decaying to e±μ∓ν, with masses between 7 and 50GeV/c 2 and lifetimes between 2 and 50 ps, are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using 5.4 fb -1 of p p collisions collected with the LHCb detector at a centre-of-mass energy of $\sqrt{s}$=13TeV. Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of 125GeV/c 2 , and the charged current production from an on-shell W boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for dark matter produced in association with a single top quark in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

This paper presents a search for dark matter in the context of a two-Higgs-doublet model together with an additional pseudoscalar mediator, a, which decays into the dark-matter particles. Processes where the pseudoscalar mediator is produced in association with a single top quark in the 2HDM+a model are explored for the first time at the LHC. Several final states which include either one or two charged leptons (electrons or muons) and a significant amount of missing transverse momentum are considered. The analysis is based on proton–proton collision data collected with the ATLAS experiment at √s = 13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb –1 . No significant excess above the Standard Model predictions is found. The results are expressed as 95% confidence-level limits on the parameters of the signal models considered.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Hint of a new scalar interaction in LHCb data?

Abstract We explain recent LHCb measurements of the lepton universality ratios, $$R_{D^{(*)}}^{\tau /\ell }\equiv \frac{\mathcal {B}(\bar{B} \rightarrow D^{(*)+} \tau ^- \bar{\nu }_\tau )}{\mathcal {B}(\bar{B} \rightarrow D^{(*)+}\ell ^- \bar{\nu }_\ell )}$$ R D ( ∗ ) τ / ℓ ≡ B ( B ¯ → D ( ∗ ) + τ - ν ¯ τ ) B ( B ¯ → D ( ∗ ) + ℓ - ν ¯ ℓ ) and $${R(\Lambda _c^+)}^{\tau /\ell } \equiv \frac{\mathcal {B}(\Lambda _b \rightarrow \Lambda _c^+ \tau ^- \bar{\nu }_{\tau })}{\mathcal {B}(\Lambda _b \rightarrow \Lambda _c^+ \ell ^- \bar{\nu }_{\ell })}$$ R ( Λ c + ) τ / ℓ ≡ B ( Λ b → Λ c + τ - ν ¯ τ ) B ( Λ b → Λ c + ℓ - ν ¯ ℓ ) with $$\ell =\mu $$ ℓ = μ , via new physics that affects $$R_D^{\tau /\ell }$$ R D τ / ℓ and $$R(\Lambda _c^+)^{\tau /\ell }$$ R ( Λ c + ) τ / ℓ but not $$R_{D^*}^{\tau /\ell }$$ R D ∗ τ / ℓ . The scalar operator in the effective theory for new physics is indicated. We find that the forward-backward asymmetry and $$\tau $$ τ polarization in $$\bar{B} \rightarrow D^+ \tau ^{-} \bar{\nu }_{\tau }$$ B ¯ → D + τ - ν ¯ τ and $$\Lambda _b \rightarrow \Lambda _c^+ \tau ^- \bar{\nu }_{\tau }$$ Λ b → Λ c + τ - ν ¯ τ decays are significantly affected by the scalar interaction. We construct a simple two Higgs doublet model as a realization of our scenario and consider lepton universality in semileptonic charm and top decays, radiative B decay, B -mixing, and $$Z \rightarrow b \bar{b}$$ Z → b b ¯ .

Physics↗
DOE OSTI2025

Search for $t\bar{t}H/A \rightarrow t\bar{t}t\bar{t}$ production in proton–proton collisions at $\sqrt{s}=13$ $\text {TeV}$ with the ATLAS detector

A search is presented for a heavy scalar (H) or pseudo-scalar (A) predicted by the two-Higgs-doublet models, where the H/A is produced in association with a top-quark pair $(t\bar{t}H/A),$ and with the H/A decaying into a $t\bar{t}$ pair. The full LHC Run 2 proton–proton collision data collected by the ATLAS experiment is used, corresponding to an integrated luminosity of $139~\text {fb}^{-1}.$ Events are selected requiring exactly one or two opposite-charge electrons or muons. Data-driven corrections are applied to improve the modelling of the $t\bar{t}$ +jets background in the regime with high jet and b-jet multiplicities. These include a novel multi-dimensional kinematic reweighting based on a neural network trained using data and simulations. An H/A-mass parameterised graph neural network is trained to optimise the signal-to-background discrimination. In combination with the previous search performed by the ATLAS Collaboration in the multilepton final state, the observed upper limits on the $t\bar{t}H/A \rightarrow t\bar{t}t\bar{t}$ production cross-section at 95% confidence level range between 14 fb and 5.0 fb for an H/A with mass between 400 GeV and 1000 GeV , respectively. Assuming that both the H and A contribute to the $t\bar{t}t\bar{t}$ cross-section, tan β values below 1.7 or 0.7 are excluded for a mass of 400 GeV or 1000 GeV , respectively. The results are also used to constrain a model predicting the pair production of a colour-octet scalar, with the scalar decaying into a $t\bar{t}$ pair.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Elementary Particle Physics (Final Report)

vATLAS and the LHC are delivering on the promise of discovery physics at the high energy frontier. Using 4.8 fb -1 of 2011 $\sqrt{s}$=7 TeV data and the first 5.8 fb -1 of 2012 $\sqrt{s}$=8 TeV data, ATLAS published the observation of a new particle with a mass of 126 GeV with a significance of 5.9σ that is compatible with a Standard Model (SM) Higgs. The LHC is outperforming initial projections for the 2012 run, and ATLAS is on track to integrate ~20 fb -1 of proton-proton collisions in 2012 before Long Shutdown 1 (LS1) begins in Spring 2013. University of Texas at Dallas (UTD) physicists will complete work on two ATLAS analyses this fall. The first is the search for the gauge bosons of a hypothesized dark sector. For 2011 data, UTD is responsible for the dark photon search in the electron-jet channel, and we are looking forward to an expanded leadership role in the dark photon search using the full 2012 data set. Our second analysis interest is the study of X/Y/Z exotic states having cc content, which builds on our experience in this field from the BABAR experiment After completing a measurement of the Xc(3872) production cross section this fall, we will search for evidence of the Z(4430)+ which is reported by Belle but not confirmed by BABAR. The UTD group has played a strong role in ATLAS operations, with group members serving as Pixel Run Coordinator, ATLAS Shift Leader, and Pixel/Inner Detector Shifter. For most of the current 3-year funding cycle, a group member coordinated the development of the Pixel DAQ code, and another continues to build and maintain the data quality monitoring (DQM) application that is used by the Inner Detector control room shifter. Additionally, members of our group take Pixel on-call expert shifts for DQM and DAQ. We led an optoboard lifetime study to assess concerns of premature on-detector VCSEL failure using the Pixel working prototype detector at CERN. Physicists based at UTD participated through Pixel Offline DQM and ATLAS Distributed Computing Operations Shifts (ADCoS) During Summer 2012, UTD joined upgrade activities in preparation for LS1. We took a major role in the testing of Electro-Readout (ER) Bundle testing for new Service Quarter Panels (nSQPs), and we developed two utilities to measure the timing jitter and bit error rate of the Pixel readout chain for use commissioning Pixel detector upgrades. During BABAR's heyday, the UTD group pioneered the use of e + e - annihilation events with hard Initial State Radiation (ISR) to study the charm threshold region, and we carried out the first BABAR double-cc analysis. Our most recent ISR paper, written in collaboration with A. Palano (Bari) is Exclusive Production of Ds + Ds - , D S *+ Ds - , and Ds *+ Ds *- via e+ e- Annihilation with Initial-State-Radiation was published in Physical Review D 82, 052004 (2010). Work continues on a study of ISR Λc + Λc - production, and a new search to establish and study double-ss production is starting.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Search for Neutral Heavy Scalars in ttZ Events Using 13 TeV pp Collisions at CMS

This thesis presents a search for a heavy pseudoscalar particle, A, which decays into a lighterscalar, H, and a Z boson within the Two-Higgs-Doublet Model (2HDM). We focus on Zboson decays to leptons, with H decays into a t t ̄ pair. The search uses the Asimov dataset–a theoretical dataset generated to predict the expected results for discovery and exclusion based on conditions from proton-proton collisions at the LHC, atintegrated luminosity of 138f b−1, as recorded by the CMS detector. The analysis focuses on events with three charged leptons, two of which come from the Z boson decay and one from a top quark decay. The expected results suggest the search has high sensitivity, showing discovery potential across much of the 2HDM Type-II parameter space, with possible deviations from the Standard Model background exceeding 5σ significance. The search sets upper limits on the cross-section times branching ratio, assuming narrow particle widths, for A masses up to 2100 GeV and H masses up to 1900 GeV. The results are interpreted in the 2HDM Type-II framework to exclude certain regions of parameter space at the 95% confidence level as a function of particle masses and variables such as tanβ and cos(β−α). The findings highlight the potential reach implications of future search in this parameter region.

Rudrabhatla, Sahithi [Illinois U., Chicago]↗