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1. Charges in the extended BMS algebra: Definitions and applications

   https://doi.org/10.21468/SciPostPhysProc.4.005  

   Porrati, Massimo (January 2021, SciPost Physics Proceedings)

   null (Ed.)

   This is a review of selected topics from recent work on symmetrycharges in asymptotically flat spacetime done by the author incollaboration with U. Kol and R. Javadinezhad. First we reinterpret thereality constraint on the boundary graviton as the gauge fixing of a newlocal symmetry, called dual supertranslations. This symmetry extends theBMS group and bears many similarities to the dual (magnetic) gaugesymmetry of electrodynamics. We use this new gauge symmetry to propose anew description of the TAUB-NUT space that does not contain closedtime-like curves. Next we summarize progress towards the definition ofLorentz and super-Lorentz charges that commute with supertranslationsand with the soft graviton mode. 

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2. Linear maps preserving the Lorentz spectrum: the $$2 \times 2$$ case

   https://doi.org/10.13001/ela.2022.6925  

   Bueno, María I.; Furtado, Susana; Klausmeier, Aelita; Veltri, Joey (December 2021, The Electronic Journal of Linear Algebra)

   In this paper, a complete description of the linear maps $$\phi:W_{n}\rightarrow W_{n}$$ that preserve the Lorentz spectrum is given when $n=2$, and $$W_{n}$$ is the space $$M_{n}$$ of $$n\times n$$ real matrices or the subspace $$S_{n}$$ of $$M_{n}$$ formed by the symmetric matrices. In both cases, it has been shown that $$\phi(A)=PAP^{-1}$$ for all $$A\in W_{2}$$, where $$P$$ is a matrix with a certain structure. It was also shown that such preservers do not change the nature of the Lorentz eigenvalues (that is, the fact that they are associated with Lorentz eigenvectors in the interior or on the boundary of the Lorentz cone). These results extend to $n=2$ those for $$n\geq 3$$ obtained by Bueno, Furtado, and Sivakumar (2021). The case $n=2$ has some specificities, when compared to the case $$n\geq3,$$ due to the fact that the Lorentz cone in $$\mathbb{R}^{2}$$ is polyedral, contrary to what happens when it is contained in $$\mathbb{R}^{n}$$ with $$n\geq3.$$ Thus, the study of the Lorentz spectrum preservers on $$W_n = M_n$$ also follows from the known description of the Pareto spectrum preservers on $$M_n$$. 

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3. Lorentz breaking and SU(2)L × U(1)Y gauge invariance for neutrinos

   https://doi.org/10.1142/S0218301319500721  

   Jentschura, U. D.; Nándori, I.; Somogyi, G. (September 2019, International Journal of Modern Physics E)

   Conceivable Lorentz-violating effects in the neutrino sector remain a research area of great general interest, as they touch upon the very foundations on which the Standard Model and our general understanding of fundamental interactions are laid. Here, we investigate the relation of Lorentz violation in the neutrino sector in light of the fact that neutrinos and the corresponding left-handed charged leptons form [Formula: see text] doublets under the electroweak gauge group. Lorentz-violating effects thus cannot be fully separated from questions related to gauge invariance. The model dependence of the effective interaction Lagrangians used in various recent investigations is explored with a special emphasis on neutrino splitting, otherwise known as the neutrino-pair Cerenkov radiation and vacuum-pair emission (electron–positron-pair Cerenkov radiation). We highlight two scenarios in which Lorentz-violating effects do not necessarily also break electroweak gauge invariance. The first of these involves a restricted set of gauge transformations, a subgroup of [Formula: see text], while in the second where differential Lorentz violation is exclusively introduced by the mixing of the neutrino flavor and mass eigenstates. Our study culminates in a model which fully preserves [Formula: see text] gauge invariance, involves flavor-dependent Lorentz-breaking parameters, and still allows for Cerenkov-type decays to proceed. 

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4. Estimating road traffic impacts of commute mode shifts

   https://doi.org/10.1371/journal.pone.0279738  

   Hu, Yue; Barbour, William; Qian, Kun; Claudel, Christian; Samaranayake, Samitha; Work, Daniel B. (January 2023, PLOS ONE)

   Jin, Sheng (Ed.)

   This work considers the sensitivity of commute travel times in US metro areas due to potential changes in commute patterns, for example caused by events such as pandemics. Permanent shifts away from transit and carpooling can add vehicles to congested road networks, increasing travel times. Growth in the number of workers who avoid commuting and work from home instead can offset travel time increases. To estimate these potential impacts, 6-9 years of American Community Survey commute data for 118 metropolitan statistical areas are investigated. For 74 of the metro areas, the average commute travel time is shown to be explainable using only the number of passenger vehicles used for commuting. A universal Bureau of Public Roads model characterizes the sensitivity of each metro area with respect to additional vehicles. The resulting models are then used to determine the change in average travel time for each metro area in scenarios when 25% or 50% of transit and carpool users switch to single occupancy vehicles. Under a 25% mode shift, areas such as San Francisco and New York that are already congested and have high transit ridership may experience round trip travel time increases of 12 minutes (New York) to 20 minutes (San Francisco), costing individual commuters $1065 and $1601 annually in lost time. The travel time increases and corresponding costs can be avoided with an increase in working from home. The main contribution of this work is to provide a model to quantify the potential increase in commute travel times under various behavior changes, that can aid policy making for more efficient commuting. 

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5. Squeezing the Parameter Space for Lorentz Violation in the Neutrino Sector with Additional Decay Channels

   https://doi.org/10.3390/particles3030041  

   Jentschura, Ulrich D. (September 2020, Particles)

   null (Ed.)

   The hypothesis of Lorentz violation in the neutrino sector has intrigued scientists for the last two to three decades. A number of theoretical arguments support the emergence of such violations, first and foremost for neutrinos, which constitute the “most elusive” and “least interacting” particles known to mankind. It is of obvious interest to place stringent bounds on the Lorentz-violating parameters in the neutrino sector. In the past, the most stringent bounds have been placed by calculating the probability of neutrino decay into a lepton pair, a process made kinematically feasible by Lorentz violation in the neutrino sector, above a certain threshold. However, even more stringent bounds can be placed on the Lorentz-violating parameters if one takes into account, additionally, the possibility of neutrino splitting, i.e., of neutrino decay into a neutrino of lower energy, accompanied by “neutrino-pair Čerenkov radiation.” This process has a negligible threshold and can be used to improve the bounds on Lorentz-violating parameters in the neutrino sector. Finally, we take the opportunity to discuss the relation of Lorentz and gauge symmetry breaking, with a special emphasis on the theoretical models employed in our calculations. 

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