Domain wall formation in late-time phase transitions

We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building

Dark matter coupling to electroweak gauge and Higgs bosons: an effective field theory approach

If dark matter is a new species of particle produced in the early universe as a cold thermal relic (a weakly-interacting massive particle-WIMP), its present abundance, its scattering with matter in direct-detection experiments, its present-day annihilation signature in indirect-detection experiments, and its production and detection at colliders, depend crucially on the WIMP coupling to standard-model (SM) particles. It is usually assumed that the WIMP couples to the SM sector through its interactions with quarks and leptons. In this paper we explore the possibility that the WIMP coupling to the SM sector is via electroweak gauge and Higgs bosons. In the absence of an ultraviolet-complete particle-physics model, we employ effective field theory to describe the WIMP--SM coupling. We consider both scalars and Dirac fermions as possible dark-matter candidates. Starting with an exhaustive list of operators up to dimension 8, we present detailed calculation of dark-matter annihilations to all possible final states, including gamma gamma, gamma Z, gamma h, ZZ, Zh, W+ W-, hh, and f fbar, and demonstrate the correlations among them. We compute the mass scale of the effective field theory necessary to obtain the correct dark-matter mass density, and well as the resulting photon line signals

False-vacuum decay in generalized extended inflation

False-vacuum decay was studied in context of generalized extended inflationary theories, and the bubble nucleation rates was computed for these theories in the limit of G(sub N) yields 0. It was found that the time dependence of the nucleation rate can be exponentially strong through the time dependence of the Jordan-Brans-Dicke field. This can have a pronounced effect on whether extended inflation can be successfully implemented

Extended inflation from higher dimensional theories

The possibility is considered that higher dimensional theories may, upon reduction to four dimensions, allow extended inflation to occur. Two separate models are analayzed. One is a very simple toy model consisting of higher dimensional gravity coupled to a scalar field whose potential allows for a first-order phase transition. The other is a more sophisticated model incorporating the effects of non-trivial field configurations (monopole, Casimir, and fermion bilinear condensate effects) that yield a non-trivial potential for the radius of the internal space. It was found that extended inflation does not occur in these models. It was also found that the bubble nucleation rate in these theories is time dependent unlike the case in the original version of extended inflation

False vacuum decay in Jordan-Brans-Dicke cosmologies

The bubble nucleation rate in a first-order phase transition taking place in a background Jordan-Brans-Dicke cosmology is examined. The leading order terms in the nucleation rate when the Jordan-Brans-Dicke field is large (i.e., late times) are computed by means of a Weyl rescaling of the fields in the theory. It is found that despite the fact that the Jordan-Brans-Dicke field (hence the effective gravitational constant) has a time dependence in the false vacuum at late times the nucleation rate is time independent

Source Scaling, Subevent Distributions, and Ground-Motion Simulation in the Composite Source Model

Predicting strong ground motion from a large earthquake depends to a large extent on the development of a realistic source model. Strong ground motion was simulated using the composite source model. F0or comparison purposes, two different approaches were implemented in the source procedure simulation. For the first approach, the source was taken as a superposition of circular subevents with a constant stress drop. The number of subevents and their radii followed fractal law distribution, specified as a spatial random field, and subevents were allowed to overlap. This resulted in the total area of the subevents being much greater than the area of the main event, in order to catch the total seismic moment conservation. For the second approach, the number of subevents and their characteristic dimensions still obeyed fractal law, but subevents were distributed randomly over the main fault and did not overlap. The total area of subevents equaled the area of the main fault. In the second approach, the subevent stress drop was left as a free parameter to be adjusted, so that the sum of the subevents’ seismic moment equalled the seismic moment of the main event. Using these two approaches, broadband ground motion was predicted from scenario earthquakes. The numerical simulations from these two approaches gave us similar results in waveform, peak ground motions, and frequency contents. The major purpose of these simulations was to address some recent criticism of the overlapping procedure (e.g., numerical implementation) used in the previous composite source model. The generally good agreement between simulated and observed ground motions from the Mw4.6 June 18, 2002, Darmstadt, Ind., earthquake and the Mw4.0 June 6, 2003, Bardwell, Ky., earthquake shown in this study indicates that the numerical techniques of the composite source model are capable of reproducing the main characteristics of ground motion, both in the near field and the far field, in the central United States

Earthquake Hazard Mitigation in the New Madrid Seismic Zone: Science and Public Policy

In the central United States, earthquake sources that are not well defined, long earthquake recurrence intervals, and uncertain ground-motion attenuation models have contributed to an overstatement of seismic hazard for the New Madrid Seismic Zone on the national seismic hazard maps published by the U.S. Geological Survey. A series of informal interviews in western Kentucky with local businesspersons, public officials, and other professionals in occupations associated with seismic-hazard mitigation discussed seismic-mitigation policies in relation to depressed local economy. Scientific and relative economic analysis was then performed using scenario earthquake models developed with the Federal Emergency management Agency\u27s Hazus-MH software. The ground-motion hazard generated by the 2008 Wenchuan, China, earthquake and seismic mitigation policies in that area were compared with those of the New Madrid Seismic Zone. Continued scientific research, additional educational opportunities for laymen and engineering professionals, and changes in the application of current earthquake science to public policy in the central United States should help improve public safety and economic development

An Update of Seismic Monitoring and Research in the Vicinity of the Paducah Gaseous Diffusion Plant: January 2018–December 2019

From January 2018 to December 2019, the Kentucky Geological Survey monitored earthquakes and conducted research on seismic hazards in the vicinity of the Paducah Gaseous Diffusion Plant, a former uranium enrichment facility, in McCracken County, western Kentucky. Six hundred forty-four earthquakes with magnitude between 0.5 and 3.7 were recorded in the area during this period. Research focused on the influence of the thick sediments on earthquake ground motion, the so-called site response, through theoretical and data analysis of borehole seismic records. Our research has shown that the National Earthquake Hazards Reduction Program site classification, which is based on Vs30, and correction factors currently being used in earthquake engineering design and other safety evaluations are not appropriate to account for site response in the area