119248930
Holographic description of the phase diagram of a chiral symmetry breaking gauge theory
The large N$ \mathcal{N} = 4 $ gauge theory with quenched $ \mathcal{N} = 2 $ quark matter in the presence of a magnetic field displays chiral symmetry breaking. We study the temperature and chemical potential dependence of this theory using its gravity dual (based on the D3/D7 brane system). With massless quarks, at zero chemical potential, the theory displays a first order thermal transition where chiral symmetry is restored and simultaneously the mesons of the theory melt. At zero temperature, these transitions with chemical potential are second order and occur at different chemical potential values. Between the three there are two tri-critical points, the positions of which we identify. At finite quark mass the second order transition for chiral symmetry becomes a cross over and there is a critical point at the end of the first order transition, while the meson melting transition remains similar to the massless quark case. We track the movement of the critical points as the mass is raised relative to the magnetic field.
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.
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.
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.
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.
12396730
The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. VII. Ophiuchus Observed with MIPS
We present maps of 14.4 deg^2 of the Ophiuchus dark clouds observed by the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). These high-quality maps depict both numerous point sources and extended dust emission within the star-forming and non–star-forming portions of these clouds. Using PSF-fitting photometry, we detect 5779 sources at 24 μm and 81 sources at 70 μm at the 10 σ level of significance. Three hundred twenty-three candidate young stellar objects (YSOs) were identified according to their positions on the MIPS/2MASS K versus color-magnitude diagrams, as compared to 24 μm detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all those with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates.
13943932
The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. VI. Perseus Observed with MIPS
We present observations of 10.6 deg^2 of the Perseus molecular cloud at 24, 70, and 160 μm with Spitzer MIPS. The images show prominent, complex extended emission dominated by illuminating B stars on the east side of the cloud and by cold filaments of 160 μm emission on the west side. Of 3950 point sources identified at 24 μm, 1141 have 2MASS counterparts. A quarter of these populate regions of the K_s versus K_s - [24] diagram that are distinct from stellar photospheres and background galaxies and thus are likely to be cloud members with infrared excess. Nearly half (46%) of these 24 μm excess sources are distributed outside the IC 348 and NGC 1333 clusters. A significant number of IRAS PSC objects are not recovered by Spitzer MIPS, most often because the IRAS objects were confused by bright nebulosity. The intercluster region contains several tightly clumped (r ~ 0.1 pc) young stellar aggregates whose members exhibit a wide variety of infrared SEDs characteristic of different circumstellar environments. This could be explained by a significant age spread among the aggregate members, or if the members formed at the same time, a remarkably rapid circumstellar evolution would be required to account for the association of Class I and Class III sources at ages ≲1 Myr. We highlight important results for the HH 211 flow, where the bow shocks are detected at both 24 and 70 μm, and for the debris disk candidate BD +31 643, where the MIPS data show the linear nebulosity to be an unrelated interstellar feature. Our data, mosaics, and catalogs are available at the Spitzer Science Archive for use by interested members of the community.
14103847
Dynamical and chemical properties of the "starless" core L1014
Spitzer Space Telescope observations of a point-like source, L1014-IRS, close to the dust peak of the low-mass dense core L1014, have raised questions about its starless nature. These show the presence of an object with colors expected for an embedded protostar with the implication that L1014-IRS would be the lowest luminosity isolated protostar known, and an ideal target with which to test star formation theories at the low mass end. In order to study its molecular content and to search for the presence of a molecular outflow, we mapped L1014 in at least one transition of 12 CO, N2H + ,H CO + , CS, and of their isotopologues 13 CO, C 18 O, C 17 O, N2D + ,a nd H 13 CO + , using the Five College Radio Astronomy Observatory (FCRAO), the IRAM 30 m antenna, and the Caltech Submillimeter Observatory (CSO). The data show physical and chemical properties in L1014 typical of moderately evolved dense cores: i.e. H2 central density of a few 10 5 molecules cm −3 , estimated mass of ∼2 M� , CO integrated depletion factor less than 10, N(N2H + ) � 6 × 10 12 cm −2 , N(N2D + )/N(N2H + ) equal to 10%, and relatively broad N2H + and N2D + lines (0.35 km s −1 ). Infall signatures and significant velocity shifts between optically thick and optically thin tracers are not observed in the line profiles. No classical signatures of molecular outflow are found in the 12 CO and 13 CO FCRAO observations. In particular, no high velocity wings are found, and no well-defined blue-red lobes of 12 CO emission are seen in the channel maps. Sensitive, higher resolution observations will clarify the presence of a molecular outflow on a smaller scale than that probed by our observations.
119267771
Fragmentation and Evolution of Molecular Clouds. III: The Effect of Dust and Gas Energetics
Dust and gas energetics are incorporated into a cluster-scale simulation of star formation in order to study the effect of heating and cooling on the star formation process. We build on our previous work by calculating separately the dust and gas temperatures. The dust temperature is set by radiative equilibrium between heating by embedded stars and radiation from dust. The gas temperature is determined using an energy-rate balance algorithm which includes molecular cooling, dust-gas collisional energy transfer, and cosmic-ray ionization. The fragmentation proceeds roughly similarly to simulations in which the gas temperature is set to the dust temperature, but there are differences. The structure of regions around sink particles has properties similar to those of Class 0 objects, but the infall speeds and mass accretion rates are, on average, higher than those seen for regions forming only low-mass stars. The gas and dust temperature have complex distributions not well modeled by approximations that ignore the detailed thermal physics. There is no simple relationship between density and kinetic temperature. In particular, high-density regions have a large range of temperatures, determined by their location relative to heating sources. The total luminosity underestimates the star formation rate at these early stages, before ionizing sources are included, by an order of magnitude. As predicted in our previous work, a larger number of intermediate-mass objects form when improved thermal physics is included, but the resulting initial mass function (IMF) still has too few low-mass stars. However, if we consider recent evidence on core-to-star efficiencies, the match to the IMF is improved.
119366547
The Impact of the Massive Young Star GL 2591 on Its Circumstellar Material: Temperature, Density, and Velocity Structure
The temperature, density, and kinematics of the gas and dust surrounding the luminous (2 × 10^4 L_☉) young stellar object GL 2591 are investigated on scales as small as ~100 AU, probed by 4.7 μm absorption spectroscopy, to over 60,000 AU, probed by single-dish submillimeter spectroscopy. These two scales are connected by interferometric 86-115 and 226 GHz images of size 30,000 AU and resolution 2000 AU in continuum and molecular lines. The data are used to constrain the physical structure of the envelope and investigate the influence of the young star on its immediate surroundings. The infrared spectra at λ/Δλ ≈ 40,000 indicate an LSR velocity of the ^(13)CO rovibrational lines of -5.7 ± 1.0 km s^(-1), consistent with the velocity of the rotational lines of CO. In infrared absorption, the ^(12)CO lines show wings out to much higher velocities, ≈-200 km s^(-1), than are seen in the rotational emission lines, which have a total width of ≈75 km s^(-1). This difference suggests that the outflow seen in rotational lines consists of envelope gas entrained by the ionized jet seen in Brγ and [S II] emission. The outflowing gas is warm, T > 100 K, since it is brighter in CO J = 6 → 5 than in lower-J CO transitions. 
The dust temperature due to heating by the young star has been calculated self-consistently as a function of radius for a power-law density distribution n = n_0r^(-α), with α = 1-2. The temperature is enhanced over the optically thin relation (T ~ r^(-0.4)) inside a radius of 2000 AU, and reaches 120 K at r ≾ 1500 AU from the star, at which point ice mantles should have evaporated. The corresponding dust emission can match the observed λ ≥ 50 μm continuum spectrum for a wide range of dust optical properties and values of α. However, consistency with the C^(17)O line emission requires a large dust opacity in the submillimeter, providing evidence for grain coagulation. The 10-20 μm emission is better matched using bare grains than using ice-coated grains, consistent with evaporation of the ice mantles in the warm inner part of the envelope. Throughout the envelope, the gas kinetic temperature as measured by H_2CO line ratios closely follows the dust temperature. The values of α and n_0 have been constrained by modeling emission lines of CS, HCN, and HCO^+ over a large range of critical densities. The best fit is obtained for α = 1.25 ± 0.25 and n_0 = (3.5 ± 1) × 10^4 cm^(-3) at r = 30,000 AU, yielding an envelope mass of (42 ± 10) M_☉ inside that radius. The derived value of α suggests that part of the envelope is in free-fall collapse onto the star. Abundances in the extended envelope are 5 × 10^(-9) for CS, 2 × 10^(-9) for H_2CO, 2 × 10^(-8) for HCN, and 1 × 10^(-8) for HCO^+. The strong near-infrared continuum emission, the Brγ line flux, and our analysis of the emission-line profiles suggest small deviations from spherical symmetry, likely an evacuated outflow cavity directed nearly along the line of sight. The A_V ≈ 30 toward the central star is a factor of 3 lower than in the best-fit spherical model. 
Compared to this envelope model, the Owens Valley Radio Observatory (OVRO) continuum data show excess thermal emission, probably from dust. The dust may reside in an optically thick, compact structure, with diameter ≾30 AU and temperature ≳1000 K, or the density gradient may steepen inside 1000 AU. In contrast, the HCN line emission seen by OVRO can be satisfactorily modeled as the innermost part of the power-law envelope, with no increase in HCN abundance on scales where the ice mantles should have been evaporated. The region of hot, dense gas and enhanced HCN abundance (~10^(-6)) observed with the Infrared Space Observatory therefore cannot be accommodated as an extension of the power-law envelope. Instead, it appears to be a compact region (r 300 K), in which high-temperature reactions are affecting abundances.