6065903
Exact results and soft breaking masses in supersymmetric gauge theory
Abstract We give an explicit formalism connecting softly broken supersymmetric gauge theories (with QCD as one limit) to N = 2 and N = 1 supersymmetric theories possessing exact solutions, using spurion fields to embed these models in an enlarged N = 1 model. The functional forms of effective lagrangian terms resulting from soft supersymmetry breaking are constrained by the symmetries of the enlarged model, although not well enough to fully determine the vacuum structure of generic softly broken models. Nevertheless, by perturbing the exact N = 1 model results with sufficiently small soft breaking masses, we show that there exist nonsupersymmetric models that exhibit monopole condensation and confinement in the same modes as the N = 1 case.
18555159
Additional fermion families and precision electroweak data
Abstract The S , T , and U formalism for studying electroweak precision data has recently been updated to include the effects of new light physics and within this analysis the latest LEP and SLC data tightly constrain models of physics beyond the Standard Model. We re-examine the constraints on additional strong and weakly interacting fermion families in the light of these developments. We conclude that the precision data favour models with at least one fermion with a mass below 150 GeV.
119206061
Hadronization at the AdS wall
We describe hadronization events, using the AdS/CFT Correspondence, which display many of the qualitative features expected in QCD. In particular we study the motion of strings with separating end points in a back-reacted hard wall geometry. The solutions show the development of a linear QCD-like string. The end points oscillate in the absence of string breaking. We introduce string breaking by hand and evolve the new state forward in time to observe the separation of two string segments. A kink associated with this breaking evolves to the end points of the string inducing rho meson production. We explicitly compute the rho meson production at the end point.
118470786
Chemical potential in the gravity dual of a 2 + 1 dimensional system
We study probe D5 branes in D3 brane AdS5 and AdS5-Schwarzschild backgrounds as a prototype dual description of strongly coupled 2+1 dimensional quasiparticles. We introduce a chemical potential through the U(1)R symmetry group, U(1) baryon number, and a U(1) of isospin in the multiflavor case. We find the appropriate D5 embeddings in each case—the embeddings do not exhibit the spontaneous symmetry breaking that would be needed for a superconductor. The isospin chemical potential does induce the condensation of charged meson states.
14538317
Field theory operator encoding in N = 2 geometries
We investigate supergravity solutions describing D5-branes wrapped on a two cycle which are dual to = 2 super Yang Mills theory. Brane probing these solutions allows the moduli space of the field theory to be identified. There are a unique set of coordinates in which the field theory on the probe takes an = 2 form and in these coordinates the running coupling of the gauge theory may be identified. We show that the geometry, when restricted to the moduli space, takes a very simple form involving only two functions. One is the running gauge coupling whilst the other parametrizes the scalar operators of the field theory. The D5-brane distributions, for the full set of solutions in the literature, can be determined by assuming the field theory's form for the running coupling as a function of scalar vevs. We show that the resulting distributions also correctly reproduce the scalar operators parametrized elsewhere providing the first non-trivial consistency check on the duality.
7462815
Softly broken SQCD: in the continuum, on the lattice, on the brane
Abstract We review progress in studying the solutions of SQCD in the presence of explicit, soft SUSY breaking terms. Massive N = 1 SQCD in the presece of a small gaugino mass leads to a controlled solution which has interesting phase structure with changing θ angle reminiscent of the QCD chiral Lagrangian. Current attempts to test the solutions of pure glue SQCD on the lattice require a theoretical understandinf of the theory with small gaugino mass in order to understand the approach to the SUSY point. We provide such a description making predictions for the gaugino condensate and lightest bound state masses. Finally we briefly review recent D-brane constructions of 4D gauge theories in string theory including a non-supersymmetric configuration. We identify this configuration with softly broken N = 2 SQCD.
6396379
A Spitzer c2d legacy survey to identify and characterize disks with inner dust holes
Understanding how disks dissipate is essential to studies of planet formation. However, identifying exactly how dust and gas dissipate is complicated due to the difficulty of finding objects that are clearly in the transition phase of losing their surrounding material. We use Spitzer Infrared Spectrograph (IRS) spectra to examine 35 photometrically selected candidate cold disks (disks with large inner dust holes). The infrared spectra are supplemented with optical spectra to determine stellar and accretion properties and 1.3 mm photometry to measure disk masses. Based on detailed spectral energy distribution modeling, we identify 15 new cold disks. The remaining 20 objects have IRS spectra that are consistent with disks without holes, disks that are observed close to edge-on, or stars with background emission. Based on these results, we determine reliable criteria to identify disks with inner holes from Spitzer photometry, and examine criteria already in the literature. Applying these criteria to the c2d surveyed star-forming regions gives a frequency of such objects of at least 4% and most likely of order 12% of the young stellar object population identified by Spitzer. We also examine the properties of these new cold disks in combination with cold disks from the literature. Hole sizes in this sample are generally smaller than in previously discovered disks and reflect a distribution in better agreement with exoplanet orbit radii. We find correlations between hole size and both disk and stellar masses. Silicate features, including crystalline features, are present in the overwhelming majority of the sample, although the 10 μm feature strength above the continuum declines for holes with radii larger than ~7 AU. In contrast, polycyclic aromatic hydrocarbons are only detected in 2 out of 15 sources. Only a quarter of the cold disk sample shows no signs of accretion, making it unlikely that photoevaporation is the dominant hole-forming process in most cases.
17017242
The Mid-Infrared Extinction Law In The Ophiuchus, Perseus, And Serpens Molecular Clouds
We compute the mid-IR extinction law from 3.6 to 24 μm in three molecular clouds—Ophiuchus, Perseus, and Serpens—by combining data from the "Cores to Disks" Spitzer Legacy Science program with deep JHKs imaging. Using a new technique, we are able to calculate the line-of-sight (LOS) extinction law toward each background star in our fields. With these LOS measurements, we create, for the first time, maps of the χ2 deviation of the data from two extinction law models. Because our χ2 maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer Infrared Array Camera (IRAC) bands, 3.6-8 μm, we see evidence for grain growth. Below , our extinction law is well fitted by the Weingartner and Draine RV = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for , the data are more consistent with the Weingartner and Draine RV = 5.5 model that uses larger maximum dust grain sizes. At 24 μm, our extinction law is 2-4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. Finally, from our χ2 maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-IR extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.
18052005
Modeling Spitzer observations of vv ser. II. An extended quantum-heated nebula and a disk shadow
We present mid-infrared Spitzer IRAC and MIPS images of the UX Orionis star VV Ser and the surrounding cloud. The 5.6-70 μm images show bright, localized, and nebulous emission extended over 4' centered on VV Ser. This nebulosity is due to transiently heated grains excited by UV photons emitted by VV Ser. Imprinted on the nebulosity is a wedge-shaped dark band, centered on the star. We interpret this as the shadow cast by the inner regions of a near-edge-on disk, allowing the PAHs to be excited only outside of this shadow. We extend an axisymmetric radiative transfer model of the VV Ser disk described in a companion paper to include quantum-heated PAH molecules and very small grains (VSGs) in the thermal cooling approximation. The presence of a disk shadow strongly constrains the inclination as well as the position angle of the disk. The nebulosity at 5.6-8.0 μm and the 2175 A absorption feature seen in an archival spectrum from the IUE can be fit using only PAHs, consistent with the main carrier of the 2175 A feature being due to the graphite-like structure of the PAHs. The PAH component is found to be relatively smoothly distributed in the cloud, while the population of VSGs emitting at 20-70 μm is strongly concentrated ~50'' to the southeast of VV Ser. Depending on the adopted PAH opacity, the abundance of PAHs in the surrounding cloud is constrained to 5% ± 2% of the total dust mass. Although relatively rare, quantum-heated nebulosities surrounding single, well-defined stars are well-suited for gaining unique insights into the physics of very small particles in molecular clouds.
122122302
Tracing the mass during low-mass star formation. II. Modeling the submillimeter emission from preprotostellar cores
We have modeled the emission from dust in preprotostellar cores, including a self-consistent calculation of the temperature distribution for each input density distribution. Model density distributions include Bonnor-Ebert spheres and power laws. The Bonnor-Ebert spheres fit the data well for all three cores that we have modeled. The dust temperatures decline to very low values (Td ~ 7 K) in the centers of these cores, strongly affecting the dust emission. Compared to earlier models that assume constant dust temperatures, our models indicate higher central densities and smaller regions of relatively constant density. Indeed, for L1544, a power-law density distribution, similar to that of a singular, isothermal sphere, cannot be ruled out. For the three sources modeled herein, there seems to be a sequence of increasing central condensation, from L1512 to L1689B to L1544. The two denser cores, L1689B and L1544, have spectroscopic evidence for contraction, suggesting an evolutionary sequence for preprotostellar cores.
119371049
Evolutionary Signatures in the Formation of Low-Mass Protostars
We present an evolutionary picture of a forming star. We assume a singular isothermal sphere as the initial state of the core that undergoes collapse, as described by Shu. We include the evolution of a first hydrostatic core at early times and allow a disk to grow, as predicted by Adams & Shu. We use a one-dimensional radiative transfer code to calculate the spectral energy distribution for the evolving protostar from the beginning of collapse to the point when all envelope material has accreted onto the star + disk system. Then, we calculate various observational signatures (Tbol, Lbol/Lsmm, and infrared colors) as a function of time. As defined by the bolometric temperature criterion, the Class 0 stage should be very short, while the Class I stage persists for much of the protostar's early life. We present physical distinctions among the classes of forming stars and calculate the observational signatures for these classes. Finally, we present models of infrared color-magnitude diagrams, as observed by the Spitzer Space Telescope, that should be strong discriminators in determining the stage of evolution for a protostar.