Physics: Faculty Publications and Other WorksCopyright (c) 2023 Loyola University Chicago All rights reserved.
https://ecommons.luc.edu/physics_facpubs
Recent documents in Physics: Faculty Publications and Other Worksen-usThu, 30 Mar 2023 10:59:39 PDT3600Experimental Radial Profiles of Early Time (<4 μs) Neutral and Ion Spectroscopic Signatures in Lightning-Like Discharges
https://ecommons.luc.edu/physics_facpubs/68
https://ecommons.luc.edu/physics_facpubs/68Thu, 08 Dec 2022 13:00:41 PST
This study presents experimental results for the radial and temporal variation of neutral and ion spectroscopic signatures emerging from the heated channel of lightning-like discharges diagnosed with a high speed (900,000 fps) imaging spectrograph. Light emissions emanate from three regions: an inner core (up to ∼2 mm), an external sheath (up to ∼4 mm) featuring a sudden temperature increase, and further optical emissions forming a dim glow from 4 mm up to 16 mm. The optical emissions are initially (
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M. Passas-Varo et al.Origin of Sterile Neutrino Dark Matter Via Secret Neutrino Interactions with Vector Bosons
https://ecommons.luc.edu/physics_facpubs/67
https://ecommons.luc.edu/physics_facpubs/67Wed, 21 Apr 2021 09:56:20 PDT
Secret neutrino interactions can play an essential role in the origin of dark matter. We present an anatomy of production mechanisms for sterile neutrino dark matter, a keV-scale gauge-singlet fermion that mixes with active neutrinos, in the presence of a new vector boson mediating secret interactions among active neutrinos. We identify three regimes of the vector boson’s mass and coupling where it makes a distinct impact on dark matter production through the dispersion relations and/or scattering rates. We also analyze models with gauged Lμ−Lτ and B−L numbers which have a similar dark matter cosmology but different vector boson phenomenology. We derive the parameter space in these models where the observed relic abundance is produced for sterile neutrino dark matter. They serve as a well-motivated target for the upcoming experimental searches.
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Kevin J. Kelly et al.Probing the Two-Neutrino Exchange Force Using Atomic Parity Violation
https://ecommons.luc.edu/physics_facpubs/66
https://ecommons.luc.edu/physics_facpubs/66Wed, 21 Apr 2021 09:56:15 PDT
The exchange of two neutrinos at one loop leads to a long-range parity-violating force between fermions. We explore the two-neutrino force in the backdrop of atomic physics. We point out that this is the largest parity-violating long-range force in the Standard Model and calculate the effect of this force in experiments that probe atomic parity violation by measuring optical rotation of light as it passes through a sample of vaporized atoms. We perform explicit calculations for the hydrogen atom to demonstrate this effect. Although we find that the effect is too small to be observed in hydrogen in the foreseeable future, our approach may be applied to other setups where long-range parity violation is large enough to be probed experimentally.
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Mitrajyoti Ghosh et al.Evidence for a Supergalactic Structure of Magnetic Deflection Multiplets of Ultra-high-energy Cosmic Rays
https://ecommons.luc.edu/physics_facpubs/65
https://ecommons.luc.edu/physics_facpubs/65Mon, 25 Jan 2021 15:00:54 PST
Evidence for a large-scale supergalactic cosmic-ray multiplet (arrival directions correlated with energy) structure is reported for ultra-high-energy cosmic-ray (UHECR) energies above 1019 eV using 7 years of data from the Telescope Array (TA) surface detector and updated to 10 years. Previous energy–position correlation studies have made assumptions regarding magnetic field shapes and strength, and UHECR composition. Here the assumption tested is that, because the supergalactic plane is a fit to the average matter density of the local large-scale structure, UHECR sources and intervening extragalactic magnetic fields are correlated with this plane. This supergalactic deflection hypothesis is tested by the entire field-of-view (FOV) behavior of the strength of intermediate-scale energy–angle correlations. These multiplets are measured in spherical cap section bins (wedges) of the FOV to account for coherent and random magnetic fields. The structure found is consistent with supergalactic deflection, the previously published energy spectrum anisotropy results of the TA (the Hotspot and Coldspot), and toy-model simulations of a supergalactic magnetic sheet. The seven year data posttrial significance of this supergalactic structure of multiplets appearing by chance, on an isotropic sky, is found by Monte Carlo simulation to be 4.2σ. The 10 years of data posttrial significance is 4.1σ. Furthermore, the starburst galaxy M82 is shown to be a possible source of the TA Hotspot, and an estimate of the supergalactic magnetic field using UHECR measurements is presented.
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Rasha U. AbbasiThe American Astronomical Society, find out more The Institute of Physics, find out more Search for Large-scale Anisotropy on Arrival Directions of Ultra-high-energy Cosmic Rays Observed with the Telescope Array Experiment
https://ecommons.luc.edu/physics_facpubs/64
https://ecommons.luc.edu/physics_facpubs/64Mon, 25 Jan 2021 15:00:48 PST
Motivated by the detection of a significant dipole structure in the arrival directions of ultra-high-energy cosmic rays above 8 EeV reported by the Pierre Auger Observatory (Auger), we search for a large-scale anisotropy using data collected with the surface detector array of the Telescope Array Experiment (TA). With 11 yr of TA data, a dipole structure in a projection of the R.A. is fitted with an amplitude of 3.3% ± 1.9% and a phase of 131° ± 33°. The corresponding 99% confidence-level upper limit on the amplitude is 7.3%. At the current level of statistics, the fitted result is compatible with both an isotropic distribution and the dipole structure reported by Auger.
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Rasha U. AbbasiGeneration of a Novel Exactly Solvable Potential
https://ecommons.luc.edu/physics_facpubs/63
https://ecommons.luc.edu/physics_facpubs/63Fri, 13 Nov 2020 09:31:21 PST
We report a new shape-invariant (SI) isospectral extension of the Morse potential. Previous investigations have shown that the list of “conventional” SI superpotentials that do not depend explicitly on Planck's constant ħ is complete. Additionally, a set of “extended” superpotentials has been identified, each containing a conventional superpotential as a kernel and additional ħ-dependent terms. We use the partial differential equations satisfied by all SI superpotentials to find a SI extension of Morse with novel properties. It has the same eigenenergies as Morse but different asymptotic limits, and does not conform to the standard generating structure for isospectral deformations.
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Jonathan Bougie et al.Can Newton’s Third Law Be “Derived” from the Second?
https://ecommons.luc.edu/physics_facpubs/62
https://ecommons.luc.edu/physics_facpubs/62Fri, 13 Nov 2020 09:31:13 PST
Newton’s laws1 have engendered much discussion over several centuries.2,3 Today, the internet is awash with a plethora of information on this topic. We find many references to Newton’s laws, often discussions of various types of misunderstandings and ways to explain them. Here we present an intriguing example that shows an assumption hidden in Newton’s third law that is often overlooked. As is well known, the first law defines an inertial frame of reference and the second law determines the acceleration of a particle in such a frame due to an external force. The third law describes forces exerted on each other in a two-particle system, and allows us to extend the second law to a system of particles. Students are often taught that the three laws are independent. Here we present an example that challenges this assumption. At first glance, it seems to show that, at least for a special case, the third law follows from the second law. However, a careful examination of the assumptions demonstrates that is not quite the case. Ultimately, the example does illustrate the significance of the concept of mass in linking Newton’s dynamical principles.
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Asim Gangopadhyaya et al.Inter-relations Between Additive Shape Invariant Superpotentials
https://ecommons.luc.edu/physics_facpubs/61
https://ecommons.luc.edu/physics_facpubs/61Fri, 13 Nov 2020 09:31:03 PST
All known additive shape invariant superpotentials in nonrelativistic quantum mechanics belong to one of two categories: superpotentials that do not explicitly depend on ħ, and their ħ-dependent extensions. The former group themselves into two disjoint classes, depending on whether the corresponding Schrödinger equation can be reduced to a hypergeometric equation (type-I) or a confluent hypergeometric equation (type-II). All the superpotentials within each class are connected via point canonical transformations. Previous work [19] showed that type-I superpotentials produce type-II via limiting procedures. In this paper we develop a method to generate a type I superpotential from type II, thus providing a pathway to interconnect all known additive shape invariant superpotentials.
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Jeffry V. Mallow, Emeritus et al.Exactness of SWKB for Shape Invariant Potentials
https://ecommons.luc.edu/physics_facpubs/60
https://ecommons.luc.edu/physics_facpubs/60Fri, 13 Nov 2020 09:30:53 PST
The supersymmetry-based semiclassical method (SWKB) is known to produce exact spectra for conventional shape invariant potentials. In this paper we prove that this exactness follows from their additive shape invariance.
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Asim Gangopadhyaya et al.The Supersymmetric WKB Formalism Is Not Exact for All Additive Shape Invariant Potentials
https://ecommons.luc.edu/physics_facpubs/59
https://ecommons.luc.edu/physics_facpubs/59Fri, 13 Nov 2020 09:30:44 PST
Following the verification of the conjecture made by Comtet et al that the supersymmetry-inspired semiclassical method known as SWKB is exact for the conventional additive shape invariant potentials, it was widely believed that SWKB yields exact results for all additive shape invariant potentials. In this paper we present a concrete example of an additive shape invariant potential for which the SWKB method fails to produce exact results.
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Jonathan Bougie et al.A First-Year Research Experience: The Freshman Project in Physics at Loyola University Chicago
https://ecommons.luc.edu/physics_facpubs/58
https://ecommons.luc.edu/physics_facpubs/58Fri, 13 Nov 2020 09:30:33 PST
Undergraduate research has become an essential mode of engaging and retaining students in physics. At Loyola University Chicago, first-year physics students have been participating in the Freshman Projects program for over twenty years, which has coincided with a period of significant growth for our department. In this paper, we describe how the Freshman Projects program has played an important role in advancing undergraduate research at Loyola and the profound impact it has made on our program. We conclude with suggestions for adoption of similar programs at other institutions.
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Jonathan Bougie et al.Dodelson-Widrow Mechanism in the Presence of Self-Interacting Neutrinos
https://ecommons.luc.edu/physics_facpubs/57
https://ecommons.luc.edu/physics_facpubs/57Mon, 26 Oct 2020 10:05:47 PDT
keV-scale gauge-singlet fermions, when allowed to mix with the active neutrinos, are elegant dark matter (DM) candidates. They are produced in the early Universe via the Dodelson-Widrow mechanism and can be detected as they decay very slowly, emitting x-rays. In the absence of new physics, this hypothesis is virtually ruled out by astrophysical observations. Here, we show that new interactions among the active neutrinos allow these sterile neutrinos to make up all the DM while safely evading all current experimental bounds. The existence of these new neutrino interactions may manifest itself in next-generation experiments, including DUNE.
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André de Gouvêa et al.Bounds on extra dimensions from micro black holes in the context of the metastable Higgs vacuum
https://ecommons.luc.edu/physics_facpubs/56
https://ecommons.luc.edu/physics_facpubs/56Fri, 18 Sep 2020 09:55:49 PDT
We estimate the rate at which collisions between ultrahigh-energy cosmic rays can form small black holes in models with extra dimensions. If recent conjectures about false vacuum decay catalyzed by black hole evaporation apply, the lack of vacuum decay events in our past light cone may place new bounds on the black hole formation rate and thus on the fundamental scale of gravity in these models. For theories with fundamental scale E∗ above the Higgs instability scale of the Standard Model, we find a lower bound on E∗ that is within about an order of magnitude of the energy where the cosmic-ray spectrum begins to show suppression from the Greisen-Zatsepin-Kuzmin effect. Otherwise, the abundant formation of semiclassical black holes with short lifetimes would likely initiate vacuum decay. Assuming a Higgs instability scale at the low end of the range compatible with experimental data, the excluded range is approximately 1017 eV≲E∗≤1018.8 eV for theories with n=1 extra dimension, narrowing to 1017 eV≲E∗≤1018.1 eV for n=6. These bounds rule out regions of parameter space that are inaccessible to collider experiments, small-scale gravity tests, or estimates of Kaluza-Klein processes in neutron stars and supernovae.
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Katherine J. Mack et al.Menagerie of AdS2 boundary conditions
https://ecommons.luc.edu/physics_facpubs/55
https://ecommons.luc.edu/physics_facpubs/55Fri, 18 Sep 2020 09:55:41 PDT
We consider different sets of AdS2 boundary conditions for the Jackiw-Teitelboim model in the linear dilaton sector where the dilaton is allowed to fluctuate to leading order at the boundary of the Poincaré disk. The most general set of boundary conditions is easily motivated in the gauge theoretic formulation as a Poisson sigma model and has an sl(2)" role="presentation" style="box-sizing: inherit; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">𝔰𝔩(2)sl(2) current algebra as asymptotic symmetries. Consistency of the variational principle requires a novel boundary counterterm in the holographically renormalized action, namely a kinetic term for the dilaton. The on-shell action can be naturally reformulated as a Schwarzian boundary action. While there can be at most three canonical boundary charges on an equal-time slice, we consider all Fourier modes of these charges with respect to the Euclidean boundary time and study their associated algebras. Besides the (centerless) sl(2)" role="presentation" style="box-sizing: inherit; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">𝔰𝔩(2)sl(2) current algebra we find for stricter boundary conditions a Virasoro algebra, a warped conformal algebra and a u(1)" role="presentation" style="box-sizing: inherit; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">𝔲(1)u(1) current algebra. In each of these cases we get one half of a corresponding symmetry algebra in three-dimensional Einstein gravity with negative cosmological constant and analogous boundary conditions. However, on-shell some of these algebras reduce to finite-dimensional ones, reminiscent of the on-shell breaking of conformal invariance in SYK. We conclude with a discussion of thermodynamical aspects, in particular the entropy and some Cardyology.
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Daniel Grumiller et al.Detection of Mg2+-dependent, coaxial stacking rearrangements in a bulged three-way DNA junction by single-molecule FRET
https://ecommons.luc.edu/physics_facpubs/54
https://ecommons.luc.edu/physics_facpubs/54Sat, 09 May 2020 10:35:33 PDT
Three-way helical junctions (3WJs) arise in genetic processing, and they have architectural and functional roles in structured nucleic acids. An internal bulge at the junction core allows the helical domains to become oriented into two possible, coaxially stacked conformers. Here, the helical stacking arrangements for a series of bulged, DNA 3WJs were examined using ensemble fluorescence resonance energy transfer (FRET) and single-molecule FRET (smFRET) approaches. The 3WJs varied according to the GC content and sequence of the junction core as well as the pyrimidine content of the internal bulge. Mg2+ titration experiments by ensemble FRET show that both stacking conformations have similar Mg2+ requirements for folding. Strikingly, smFRET experiments reveal that a specific junction sequence can populate both conformers and that this junction undergoes continual interconversion between the two stacked conformers. These findings will support the development of folding principles for the rational design of functional DNA nanostructures.
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Michael P. Leveille et al.Conservation Laws and Energy Transformations in a Class of Common Physics Problems
https://ecommons.luc.edu/physics_facpubs/53
https://ecommons.luc.edu/physics_facpubs/53Tue, 21 Apr 2020 13:45:56 PDT
We analyze a category of problems that is of interest in many physical situations, including those encountered in introductory physics classes: systems with two well-delineated parts that exchange energy, eventually reaching a shared equilibrium with a loss of mechanical or electrical energy. Such systems can be constrained by a constant of the system (e.g., mass, charge, momentum, or angular momentum) that uniquely determines the mechanical or electrical energy of the equilibrium state, regardless of the dissipation mechanism. A representative example would be a perfectly inelastic collision between two objects in one dimension, for which momentum conservation requires that some of the initial kinetic energy is dissipated by conversion to thermal or other forms as the two objects reach a common final velocity. We discuss how this feature manifests in a suite of four well-known and disparate problems that all share a common mathematical formalism. These examples, in which the energy dissipated during the process can be difficult to solve directly from dissipation rates, can be approached by students in a first-year physics class by considering conservation laws and can therefore be useful for teaching about energy transformations and conserved quantities. We then illustrate how to extend this method by applying it to a final example.
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Jonathan Bougie et al.Singlet-Doublet Dirac Dark Matter and Neutrino Masses
https://ecommons.luc.edu/physics_facpubs/52
https://ecommons.luc.edu/physics_facpubs/52Tue, 21 Apr 2020 13:45:47 PDT
We examine an extension of the Standard Model that addresses the dark matter puzzle and generates Dirac neutrino masses through the radiative seesaw mechanism. The new field content includes a scalar field that plays an important role in setting the relic abundance of dark matter. We analyze the phenomenology in the light of direct, indirect, and collider searches of dark matter. In this framework, the dark matter candidate is a Dirac particle that is a mixture of new singlet-doublet fields with mass mχ01≲1.1 TeV. We find that the allowed parameter space of this model is broader than the well-known Majorana dark matter scenario.
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Diego Restrepo et al.Mario Kart 8: A Case Study In Total Internal Reflection
https://ecommons.luc.edu/physics_facpubs/51
https://ecommons.luc.edu/physics_facpubs/51Mon, 04 Nov 2019 07:15:50 PSTRobert Polak et al.Building Confidence in the Dirac δ-function
https://ecommons.luc.edu/physics_facpubs/50
https://ecommons.luc.edu/physics_facpubs/50Tue, 04 Dec 2018 10:13:19 PST
In this note we present an example from undergraduate quantum mechanics designed to highlight the versatility of the Dirac δ-function. Namely, we compute the expectation value of the Hamiltonian of a free particle in a state described by a triangular wave function ψ(x). Since the first derivative of ψ(x) is piecewise constant, and because this Hamiltonian is proportional to the second order spatial derivative, students often end up finding the expectation value to be zero—an unphysical answer. This problem provides a pedagogical application of the Dirac δ-function. By arriving at the same result via alternate pathways, this exercise reinforces students’ confidence in the Dirac δ-function and highlights its efficiency and elegance.
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Asim Gangopadhyaya et al.Galileo's Contribution to Mechanics
https://ecommons.luc.edu/physics_facpubs/49
https://ecommons.luc.edu/physics_facpubs/49Fri, 15 Jun 2018 15:57:46 PDT
Asim Gangopadhyaya writes about Galileo's contributions to mechanics and physics in this chapter in Where Have All the Heavens Gone? Galileo's Letter to the Grand Duchess Christina edited by John P. McCarthy and Edmondo F. Lupieri.
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Asim Gangopadhyaya