Charge conjugation from space-time inversion in QED: discrete and continuous groups

We show that the CPT groups of QED emerge naturally from the PT and P (or T) subgroups of the Lorentz group. We also find relationships between these discrete groups and continuous groups, like the connected Lorentz and Poincar\'e groups and their universal coverings.Comment: 7 page

Los juegos de pelota en el Altiplano Central de México

The following represents a pre-press draft submitted in English and subsequently translated to Spanish.Los juegos de pelota más antiguos de Mesoamérica se encuentran en las Tierras Bajas; sin embargo, los habitantes del Altiplano Central adoptaron y construyeron canchas formales desde principios del Preclásico Medio. En periodos posteriores, el predominio de canchas varió según el sitio, los contactos regionales y las tendencias sociopolíticas más generales. Las canchas de juegos de pelota fueron particularmente numerosas en Puebla y Tlaxcala hacia finales del periodo Preclásico, y abundantes durante el Epiclásico en todo el Altiplano Central de México. Las mejores descripciones de cómo se jugó pelota en toda Mesoamérica durante los tiempos prehispánicos provienen de documentos del siglo xvi, del Altiplano; incluso el juego fue llevado a España por Cortés.Although the earliest ball-courts appear in the Mesoamerican lowlands, the inhabitants of the central highlands eagerly adopted and elaborated formal courts beginning during the Middle Preclassic period. In subsequent periods, the prevalence of ball-courts varied by site, regional contacts and broader sociopolitical forces. Courts were particularly numerous in Puebla-Tlaxcala during the later Preclassic period and throughout cent ral Mexico during the Epiclassic period. Sixteenth century documents from the Altiplano provide the best descriptions concerning how prehispanic games throughout Mesoamerica were played, even having been exported to Spain by Cortés (Figure 1)

Aztec obsidian industries

Obsidian was the primary lithic or stone material used for cutting activities in Aztec society, including domestic food production, craft production, hunting, warfare, and ritual. The demands of millions of consumers within and outside of the Aztec Empire shaped a diversity of industries and distribution networks that operated through merchants, markets, and state taxes in goods and labor. This chapter provides an overview of the primary obsidian sources, quarry activities, artifact types, use contexts, and innovations in lithic technology during the Aztec (Middle and Late Postclassic) period. A particular focus is the Sierra de Las Navajas (or Pachuca) mine and the detailed history of quarrying and manufacturing activities that have been documented there

Bridging prehistory and history in the archaeology of cities

Archaeology is ideally suited for examining the deep roots of urbanism, its materialization and physicality, and the commonalities and variability in urban experiences cross-culturally and temporally. We propose that the significant advances archaeologists have made in situating the discipline within broader urban studies could be furthered through increased dialog between scholars working on urbanism during prehistoric and historical periods, as a means of bridging concerns in the study of the past and present. We review some major themes in urban studies by presenting archaeological cases from two areas of the Americas: central Mexico and Atlantic North America. Our cases span premodern and early modern periods, and three of the four covered in greatest depth live on as cities of today. Comparison of the cases highlights the complementarity of their primary datasets: the long developmental trajectories and relatively intact urban plans offered by many prehistoric cities, and the rich documentary sources offered by historic cities

Lithic economies and community organization at La Laguna, Tlaxcala

Site-wide, assemblage-based lithic analyses help to elucidate community dynamics including variability in domestic economies, technological skill and decision making, exchange networks, and ritual practices. In this study we present the results of an analysis of over 36,000 lithic artifacts from the site of La Laguna, Tlaxcala. We compare Middle to Late Formative period (ca. 600–400 b.c.) and Terminal Formative period (ca. 100 b.c.–a.d. 150) deposits to examine transformations associated with urbanization and state formation during this interval. The residents of La Laguna had relatively equal and ample access to obsidian, and most production was organized independently by households. We identify blade production zones and variability in consumption patterns suggestive of different domestic, communal, and ceremonial activities. The introduction of bloodletters, elaborate large bifacial knives, and zoomorphic eccentrics to the Terminal Formative assemblage may indicate the emergence of higher statuses, new social roles, and militaristic symbolism during this period