119389101
A One-Scale Model of Dynamical Supersymmetry Breaking
A model of gauge-mediated supersymmetry breaking is constructed in which the low-energy physics depends on a single dynamical scale. The strong coupling dynamics of gauge theories plays an important role, in particular through its effects on beta functions and through confinement. The model does not have distinct messenger and supersymmetry-breaking sectors. The scale of supersymmetry breaking is of the order of 10{endash}100 TeV, implying that the decay of the next-to-lightest superpartner into the gravitino is prompt. Superoblique corrections are enhanced. A Dirac fermion and one complex scalar, in a 10 or {ovr 10} of (global) SU(5), are predicted to be relatively light and to satisfy certain mass relations with the standard model squarks and sleptons. {copyright} {ital 1999} {ital The American Physical Society}
19576396
Short baseline neutrino oscillations and a new light gauge boson
12 pages, 4 figures.-- PACS number: 14.60.Pq.-- Submitted on 8 Nov 2007 (v1), last revised 21 Dec 2007 (this version, v3): References added, minor change to coupling constraints, expanded sections on astrophysical and cosmological constraints.-- Published in: Phys. Rev. D 77, 033001 (2008) (12 pages).-- Final full-text version of the paper available at: http://dx.doi.org/10.1103/PhysRevD.77.033001.
120299157
Operator analysis of proton decay in an SU(7) gut
Abstract An SU(7) model, with a surviving low-energy SU(4) × SU(3) × U(1) gauge symmetry, may reduce the number of low-energy effective four-fermion baryon number violating interactions from six to two. A simple argument, applicable to general SU ( N ), shows that the terms allowed by SU(4) × SU(3) × U(1) are the same as those allowed by SU(7).
13301753
Dynamical supersymmetry breaking at low energies.
Conventional approaches to supersymmetric model building suffer from several naturalness problems: they do not explain the large hierarchy between the weak scale and the Planck mass, and they require fine-tuning to avoid large flavor-changing neutral currents and particle electric dipole moments. The existence of models with dynamical supersymmetry breaking, which can explain the hierarchy, has been known for some time, but efforts to build such models have suffered from unwanted axions and difficulties with asymptotic freedom. In this paper we describe an approach to model building with supersymmetry broken at comparatively low energies which solves these problems, and give a realistic example.
122944590
CP violation and Fritzsch mass matrices
Abstract We discuss a form for the quark mass matrices which produces maximal weak but no string CP violation. The quark mass matrices are of the Fritzsch type, with all phases equal to multiples of 1 2 π . We show that these matrices can be produced in an SO(10) model with CP violated spontaneously at the GUT scale. The model successfully predicts the entire K-M matrix. Radiative corrections to θ , however, are several orders of magnitude too large in the model, and θ is naturally of O(10 −5 ).
14203692
Dark energy from mass varying neutrinos
We show that mass varying neutrinos (MaVaNs) can behave as a negative pressure fluid which could be the origin of the cosmic acceleration. We derive a model independent relation between the neutrino mass and the equation of state parameter of the neutrino dark energy, which is applicable for general theories of mass varying particles. The neutrino mass depends on the local neutrino density and the observed neutrino mass can exceed the cosmological bound on a constant neutrino mass. We discuss microscopic realizations of the MaVaN acceleration scenario, which involve a sterile neutrino. We consider naturalness constraints for mass varying particles, and find that both eV cut-offs and eV mass particles are needed to avoid fine-tuning. In microscopic realizations of this scenario with a sterile neutrino, these considerations give the sterile neutrino a maximum mass today of order an eV, which could be detectable at MiniBooNE. Because the sterile neutrino was much heavier at earlier times, constraints from big bang nucleosynthesis on additional states are not problematic. We consider regions of high neutrino density and find that the most likely place today to find neutrino masses which are significantly different from the neutrino masses in our solar system is in a supernova. The possibility of different neutrino mass in different regions of the galaxy and the local group could be significant for Z-burst models of ultra-high energy cosmic rays. We also consider the cosmology of and the constraints on the 'acceleron', the scalar field which is responsible for the varying neutrino mass, and briefly discuss neutrino density dependent variations in other constants, such as the fine structure constant.
117045776
Dynamics and observational appearance of circumstellar disks
In my thesis I present a study of the dynamics and observational characteristics of massive circumstellar disks in two dimensions ($r$, $\phi$) using two complimentary hydrodynamic codes: a `Smoothed Particle Hydrodynamic' (SPH) code and a `Piecewise Parabolic Method' (PPM) code. I also study the detection limits available to radial velocity searches for low mass companions to main sequence stars. The thesis is organized as a series of published or submitted papers, connected by introductory and concluding material and is archived `for posterity'. I recommend that readers of this abstract obtain the published versions of each of these papers. I first outline the progress which has been made in the modeling of the structure and origins of the solar system, then in chapter 2 (ApJ 502,p342) I proceed with numerical simulations of circumstellar disks using both hydrodynamic codes assuming a `locally isothermal' equation of state. In chapter 4 (ApJ submitted) I relax the locally isothermal evolution assumption and instead include simple heating and cooling prescriptions for the system. In chapter 6 (ApJ 500,p940) I examine the limits which may be placed upon the detection of planets, brown dwarfs and low mass stellar companions using radial velocity measurements. In chapter 7, I outline several problems which may be profitably addressed by building on this work.
5533361
The Range of Masses and Periods Explored by Radial Velocity Searches for Planetary Companions
Radial velocity measurements have proven a powerful tool for finding planets in short-period orbits around other stars. In this paper we develop an analytical expression relating the sensitivity to a periodic signal to the duration and accuracy of a given set of data. The effects of windowing and the sensitivity to periods longer than the total length of observations are explored. We show that current observations are not yet long or accurate enough to make unambiguous detection of planets with the same mass and period as Jupiter. However, if measurements are continued at the current levels of accuracy (5 m s-1) for a decade, then planets of Jovian mass and brown dwarfs will either be detected or ruled out for orbits with periods less than ~15 yr. As specific examples, we outline the performance of our technique on large-amplitude and large-eccentricity radial velocity signals recently discussed in the literature, and we delineate the region explored by the measurements of 14 single stars made over a 12 yr period by Walker et al. Had any of these stars shown motion like that caused by the exoplanets recently detected, it would have been easily detected. The data set interesting limits on the presence of brown dwarfs at orbital radii of 5-10 AU. The most significant features in the Walker et al. data are apparent long-term velocity trends in 36 UMa and β Vir, consistent with super planets of mass of 2 MJ in a 10 yr period, or 20-30 MJ in a 50 yr period. If the data are free of long-term systematic errors, the probability of just one of the 14 stars showing this signal by chance is about 15%. Finally, we suggest an observing strategy for future large radial velocity surveys that, if implemented, will allow coverage of the largest range of parameter space with the smallest amount of observing time per star. We suggest that about 10-15 measurements be made of each star in the first 2 yr of the survey, then 2-3 measurements yr-1 thereafter, provided no (or slow) variation is observed. More frequent observations would of course be indicated if such variations were present.
64863479
Dynamics of Core Accretion
We perform 3-dimensional hydrodynamic simulations of gas flowing around a plan- etary core of mass Mpl=10Membedded in a near Keplerian background flow, using a modified shearing box approximation. We assume an ideal gas behavior following an equation of state with a fixed ratio of the specific heats, γ = 1.42, consistent with the conditions of a moderate temperature background disk with solar composition. No radiative heating or cooling is included in the models. We employ a nested grid hydrodynamic code implementing the 'Piecewise Parabolic Method' with as many as six fixed nested grids, providing spatial resolution on the finest grid comparable to the present day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static en- velope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disk. It is sensitive to the thermodynamic treatment of the gas, as modeled by prescribed equations of state (either 'locally isothermal' or 'locally isentropic') and the temperature of the background disk material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. Each of these factors influence the magnitude and character of hydrodynamic feedback of the small scale flow on the background, and we conclude that accurate modeling of such feedback is critical to a complete understanding of the core accretion process. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. No net mass accretion into the envelope is observed over the course of the simulation and none is expected, due to our neglect of cooling. Except in cases of very rapid cooling however, as defined by locally isothermal or isentropic treatments, any cooling that does affect the envelope material will have limited consequences for the dynamics, since the flow quickly carries cooled material out of the core's environment entirely. The angular momentum of material in the envelope, relative to the core, varies both in magnitude and in sign on time scales of days to months near the core and on time scales a few years at distances comparable to the Hill radius. The dynamical activity contrasts with the largely static behavior typically assumed within the framework of the core accretion model for Jovian planet formation. We show that material entering the dynamically active environment may suffer intense heating and cooling events the durations of which are as short as a few hours to a few days. Shorter durations are not observable in our work due to the limits of our resolution. Peak temperatures in these events range from T � 1000 K to as high as T � 3 4000 K, with densities ρ � 10 9 10 8 g/cm 3 . These time scales, densities and temperatures span a range consistent with those required for chondrule formation in the nebular shock model. We therefore propose that dynamical activity in the Jovian planet formation environment could be responsible for the production of chondrules and other annealed silicates in the solar nebula.
282379
Planet Formation is Unlikely in Equal-Mass Binary Systems with a ~ 50 AU
We show that planet formation via both gravitational collapse and core accretion is unlikely to occur in equal-mass binary systems with moderate (~50 AU) semimajor axes. Internal thermal energy generation in the disks is sufficient to heat the gas everywhere so that spiral structures quickly decay rather than grow or fragment. This same heating will inhibit dust coagulation because the temperatures rise above the vaporization temperatures of many volatile materials. We consider other processes not included in the model and conclude that our temperatures are conservatively estimated (low), i.e., planet formation is less likely in real systems than in the model.
12208225
VINE—A NUMERICAL CODE FOR SIMULATING ASTROPHYSICAL SYSTEMS USING PARTICLES. I. DESCRIPTION OF THE PHYSICS AND THE NUMERICAL METHODS
We present a numerical code for simulating the evolution of astrophysical systems using particles to represent the underlying fluid flow. The code is written in Fortran 95 and is designed to be versatile, flexible and extensible, with modular options that can be selected either at the time the code is compiled or at run time through a text input file. We include a number of general purpose modules describing a variety of physical processes commonly required in the astrophysical community and we expect that the effort required to integrate additional or alternate modules into the code will small. In its simplest form the code can evolve the dynamical trajectories of a set of particles in two or three dimensions using a module which implements either a Leapfrog or Runge-Kutta-Fehlberg integrator, selected by the user at compile time. The user may choose to allow the integrator to evolve the system using individual timesteps for each particle or with a single, global time step for all. Particles may interact gravitationally as N-body particles, and all or any subset may also interact hydrodynamically, using the Smoothed Particle Hydrodynamic (SPH) method by selecting the SPH module. A third particle species can be included with a module to model massive point particles which may accrete nearby SPH or N-body particles. Such particles may be used to model, e.g., stars in a molecular cloud. Free boundary conditions are implemented by default, and a module may be selected to include periodic boundary conditions. We use a binary ‘Press’ tree to organize particles for rapid access in gravity and SPH calculations. Modules implementing an interface with special purpose ‘GRAPE’ hardware may also be selected to accelerate the gravity calculations. If available, forces obtained from the GRAPE coprocessors may be transparently substituted for those obtained from the tree, or both tree and GRAPE may be used as a combination GRAPE/tree code. The code may be run without modification on single processors or in parallel using OpenMP compiler directives on large scale, shared memory parallel machines. We present simulations of several test problems, including a merger simulation of two elliptical galaxies with 800000 particles. In comparison to the Gadget-2 code of Springel (2005), the gravitational force calculation, which is the most costly part of any simulation including self-gravity, is ∼ 4.6 − 4.9 times faster with VINE when tested on different snapshots of the elliptical galaxy merger simulation when run on an Itanium 2 processor in an SGI Altix. A full simulation of the same setup with 8 processors is a factor of 2.91 faster with VINE. The code is available to the public under the terms of the Gnu General Public License. Subject headings: methods: numerical — methods: N-body simulations — galaxies: interactions