125436343
Holographic QCD and perfection
A holographic description of chiral symmetry breaking in the pattern of QCD is reviewed. D7 brane probes are used to include quark fields in a simple non-supersymmetric deformation of the AdS/CFT Correspondence. The axial symmetry breaking is realized geometrically and the quark condensate and meson masses are computable. Surprisingly, treating the model as a description of QCD works quantitatively at the 15% level. Models of this AdS/QCD type typically have a strongly coupled, conformal UV regime that is far from QCD. To systematically move closer to QCD, we propose cutting out the large radius gravitational description and matching operators and couplings at a finite UV cut off in the spirit of a perfect lattice action. A simple example is discussed.
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.
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.
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.
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.
118938125
c2d Spitzer IRS Spectra of Disks around T Tauri Stars. I. Silicate Emission and Grain Growth
Infrared ~5-35 μm spectra for 40 solar mass T Tauri stars and 7 intermediate-mass Herbig Ae stars with circumstellar disks were obtained using the Spitzer Space Telescope as part of the c2d IRS survey. This work complements prior spectroscopic studies of silicate infrared emission from disks, which were focused on intermediate-mass stars, with observations of solar mass stars limited primarily to the 10 μm region. The observed 10 and 20 μm silicate feature strengths/shapes are consistent with source-to-source variations in grain size. A large fraction of the features are weak and flat, consistent with micron-sized grains indicating fast grain growth (from 0.1 to 1.0 μm in radius). In addition, approximately half of the T Tauri star spectra show crystalline silicate features near 28 and 33 μm, indicating significant processing when compared to interstellar grains. A few sources show large 10-to-20 μm ratios and require even larger grains emitting at 20 μm than at 10 μm. This size difference may arise from the difference in the depth into the disk probed by the two silicate emission bands in disks where dust settling has occurred. The 10 μm feature strength versus shape trend is not correlated with age or Hα equivalent width, suggesting that some amount of turbulent mixing and regeneration of small grains is occurring. The strength versus shape trend is related to spectral type, however, with M stars showing significantly flatter 10 μm features (larger grain sizes) than A/B stars. The connection between spectral type and grain size is interpreted in terms of the variation in the silicate emission radius as a function of stellar luminosity, but could also be indicative of other spectral-type-dependent factors (e.g., X-rays, UV radiation, and stellar/disk winds).
18887854
Studies of Low-Mass Star Formation with ALMA
ALMA will revolutionize the study of star formation by providing a combination of angular resolution and sensitivity that far exceeds that of present instruments. I will focus on studies of relatively isolated cores that are forming low-mass stars. There is a general paradigm for the formation of such stars, and there are detailed theoretical predictions for the evolution of the density and velocity fields for different assumptions about the initial conditions. Because the theory is well developed, observational tests are particularly revealing. The primary probes of physical conditions in these regions are discussed and the sensitivity of ALMA to these probes is shown and compared to the current state of the art. The consequences for the ALMA requirements are discussed.
119478666
A CS J = 5 ->4 Mapping Survey Towards High Mass Star Forming Cores Associated with H2O Masers
Sixty-three high mass star forming cores selected from the study of Plume et al. (1997; T ∗ R > 1K) were mapped in CS J= 5 → 4 at the CSO between September 1996 and July 1999. Nearly all of the cores observed lie in the first and second galactic quadrants. The cores were mapped using the on-the-fly technique with a square grid in RA-DEC coordinates oversampled at 10 resolution. The maps were extended until the CS emission was negligible (±50 for the average map).
119015950
Evidence for J- and H-Band Excess in Classical T Tauri Stars and the Implications for Disk Structure and Estimated Ages
We argue that classical T Tauri stars (CTTSs) possess significant nonphotospheric excess in the J and H bands (1.25 and 1.66 μm, respectively). We first show that normalizing the spectral energy distributions (SEDs) of CTTSs to the J band leads to a poor fit of the optical fluxes (which are systematically overestimated), while normalizing the SEDs to the IC band (0.8 μm) produces a better fit to the optical bands and in many cases reveals the presence of a considerable excess at J and H. Near-infrared spectroscopic veiling measurements from the literature support this result. We find that J- and H-band excesses correlate well with the K-band (2.2 μm) excess and that the J - K and H - K colors of the excess emission are consistent with that of a blackbody at the dust sublimation temperature (~1500-2000 K). We propose that this near-IR excess originates at a hot inner rim, analogous to those suggested to explain the "near-IR bump" in the SEDs of Herbig Ae/Be stars. To test our hypothesis, we use the model presented by Dullemond and coworkers to fit the photometry data between 0.5 and 24 μm of 10 CTTSs associated with the Chamaeleon II molecular cloud. We find that simple models that include luminosities calculated from IC-band magnitudes and an inner rim may account for the reported J- and H-band excesses. The models that best fit the data are those in which the inner radius of the disk is larger than expected for a rim in thermal equilibrium with the photospheric radiation field alone. In particular, we find that large inner rims are necessary to account for the mid-infrared fluxes (3.6-8.0 μm) obtained by the Spitzer Space Telescope (Spitzer). The large radius could be explained if, as proposed by D'Alessio and colleagues, the UV radiation from the accretion shock significantly affects the sizes of the inner holes in disks around CTTSs. Finally, we argue that deriving the stellar luminosities of CTTSs by making bolometric corrections to the J-band fluxes, which is the "standard" procedure for obtaining CTTS luminosities, systematically overestimates these luminosities. The overestimated luminosities translate into underestimated ages when the stars are placed in the H-R diagram. Thus, the results presented herein have important implications for the dissipation timescale of inner accretion disks.
119625104
c2d Spitzer IRS Spectra of Disks around T Tauri Stars. III. [Ne II], [Fe I], and H2 Gas-Phase Lines
We present a survey of mid-infrared gas-phase lines toward a sample of 76 circumstellar disks around low-mass pre-main-sequence stars from the Spitzer "Cores to Disks" legacy program. We report the first detections of [Ne II] and [Fe I] toward classical T Tauri stars in ~20% and ~9% of our sources, respectively. The observed [Ne II] line fluxes and upper limits are consistent with [Ne II] excitation in an X-ray irradiated disk around stars with X-ray luminosities L_X = 10^(29)-10^(31) erg s^(-1). [Fe I] is detected at ~10^(-5) to 10^(-4) L_⊙, but no [S I] or [Fe II] is detected down to ~10^(-6) L_⊙. The [Fe I] detections indicate the presence of gas-rich disks with masses of ≳ 0.1 M_J. No H_2 0-0 S(0) and S(1) disk emission is detected, except for S(1) toward one source. These data give upper limits on the warm (T ~ 100-200 K) gas mass of a few Jovian masses, consistent with recent T Tauri disk models that include gas heating by stellar radiation. Compact disk emission of hot (T ≳ 500 K) gas is observed through the H_2 0-0 S(2) and/or S(3) lines toward ~8% of our sources. The line fluxes are, however, higher by more than an order of magnitude than those predicted by recent disk models, even when X-ray and excess UV radiation are included. The [Ne II]/H_2 0-0 S(2) ratios for these sources are similarly lower than predicted, consistent with the presence of an additional hot molecular gas component not included in current disk models. Oblique shocks of stellar winds interacting with the disk can explain many aspects of the hot gas emission but are inconsistent with the nondetection of [S I] and [Fe II] lines.