The Hierarchy Principle and the Large Mass Limit of the Linear Sigma Model

In perturbation theory we study the matching in four dimensions between the linear sigma model in the large mass limit and the renormalized nonlinear sigma model in the recently proposed flat connection formalism. We consider both the chiral limit and the strong coupling limit of the linear sigma model. Our formalism extends to Green functions with an arbitrary number of pion legs,at one loop level,on the basis of the hierarchy as an efficient unifying principle that governs both limits. While the chiral limit is straightforward, the matching in the strong coupling limit requires careful use of the normalization conditions of the linear theory, in order to exploit the functional equation and the complete set of local solutions of its linearized form.Comment: Latex, 41 pages, corrected typos, final version accepted by IJT

The Role of Bulge Formation in the Homogenization of Stellar Populations at z∼2z\sim2 as revealed by Internal Color Dispersion in CANDELS

We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relate to the formation of galaxies at $1.5 < z < 3.5$. We use the Internal Color Dispersion (ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with S\'{e}rsic indexes $< 2$) and stellar masses between $10 < \mathrm{Log~M/ M_\odot}< 11$. There is a marked decrease in the ICD as the stellar mass and/or the S\'ersic index increases. By studying the relations between the ICD and other galaxy properties including sizes, total colors, star-formation rate, and dust attenuation, we conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high star-forming clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, $10 < \mathrm{Log~M/ M_\odot} < 11$, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses, and/or higher S\'{e}rsic index ($n > 2$) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have both a quiescent bulge along with a star forming disk, typical of Hubble Sequence galaxies, this is most common for stellar masses $10 < \mathrm{Log~M/M_\odot} < 11$ and when the bulge component remains relatively small ($n<2$).Comment: 15 pages, 14 figure

The Space Density and Colors of Massive Galaxies at 2<z<3: the Predominance of Distant Red Galaxies

Using the deep multi-wavelength MUSYC, GOODS, and FIRES surveys we construct a stellar mass-limited sample of galaxies at 2<z<3. The sample comprises 294 galaxies with M>10^11 Solar masses distributed over four independent fields with a total area of almost 400 sq arcmin. The mean number density of massive galaxies in this redshift range is (2.2+-0.6) x 10^-4 Mpc^-3. We present median values and 25th and 75th percentiles for the distributions of observed R mags, observed J-K colors, and rest-frame UV continuum slopes, M/L(V) ratios, and U-V colors. The galaxies show a large range in all these properties. The ``median galaxy'' is faint in the observer's optical (R=25.9), red in the observed near-IR (J-K=2.48), has a rest-frame UV spectrum which is relatively flat (beta=-0.4), and rest-frame optical colors resembling those of nearby spiral galaxies (U-V=0.62). We determine which galaxies would be selected as Lyman break galaxies (LBGs) or Distant Red Galaxies (DRGs, having J-K>2.3) in this mass-limited sample. By number DRGs make up 69% of the sample and LBGs 20%, with a small amount of overlap. By mass DRGs make up 77% and LBGs 17%. Neither technique provides a representative sample of massive galaxies at 2<z<3 as they only sample the extremes of the population. As we show here, multi-wavelength surveys with high quality photometry are essential for an unbiased census of massive galaxies in the early Universe. The main uncertainty in this analysis is our reliance on photometric redshifts; confirmation of the results presented here requires extensive near-infrared spectroscopy of optically-faint samples.Comment: Accepted for publication in ApJ Letter

Of Higgs, Unitarity and other Questions

On the verge of conclusive checks on the Standard Model by the LHC, we discuss some of the basic assumptions. The reason for this analysis stems from a recent proposal of an Electroweak Model based on a nonlinearly realized gauge group SU(2) X U(1), where, in the perturbative approximation, there is no Higgs boson. The model enjoys the Slavnov-Taylor identities and therefore the perturbative unitarity. On the other hand, it is commonly believed that the existence of the Higgs boson is entangled with the property of unitarity, when high energy processes are considered. The argument is based mostly on the Froissart bound and on the Equivalence Theorem. In this talk we briefly review some of our objections on the validity of such arguments. Some open questions are pointed out, in particular on the limit of zero mass for the vector mesons and on the fate of the longitudinal polarizations.Comment: 23 pages, 1 figure, presented by Ruggero Ferrari at the International Conference "Gauge Fields. Yesterday, Today, Tomorrow" in honor of A.A. Slavnov. Moscow, January 19-24 201

Genomic diversity of EPEC associated with clinical presentations of differing severity

Enteropathogenic Escherichia coli (EPEC) are diarrhoeagenic E. coli, and are a significant cause of gastrointestinal illness among young children in developing countries. Typical EPEC are identified by the presence of the bundle-forming pilus encoded by a virulence plasmid, which has been linked to an increased severity of illness, while atypical EPEC lack this feature. Comparative genomics of 70 total EPEC from lethal (LI), non-lethal symptomatic (NSI) or asymptomatic (AI) cases of diarrhoeal illness in children enrolled in the Global Enteric Multicenter Study was used to investigate the genomic differences in EPEC isolates obtained from individuals with various clinical outcomes. A comparison of the genomes of isolates from different clinical outcomes identified genes that were significantly more prevalent in EPEC isolates of symptomatic and lethal outcomes than in EPEC isolates of asymptomatic outcomes. These EPEC isolates exhibited previously unappreciated phylogenomic diversity and combinations of virulence factors. These comparative results highlight the diversity of the pathogen, as well as the complexity of the EPEC virulence factor repertoire

The distribution of satellites around massive galaxies at 1<z<3 in ZFOURGE/CANDELS: dependence on star formation activity

We study the statistical distribution of satellites around star-forming and quiescent central galaxies at 1<z<3 using imaging from the FourStar Galaxy Evolution Survey (ZFOURGE) and the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The deep near-IR data select satellites down to $\log(M/M_\odot)>9$ at z<3. The radial satellite distribution around centrals is consistent with a projected NFW profile. Massive quiescent centrals, $\log(M/M_\odot)>10.78$, have $\sim$2 times the number of satellites compared to star-forming centrals with a significance of 2.7$\sigma$ even after accounting for differences in the centrals' stellar-mass distributions. We find no statistical difference in the satellite distributions of intermediate-mass quiescent and star-forming centrals, $10.48<\log(M/M_\odot)<10.78$. Comparing to the Guo2011 semi-analytic model, the excess number of satellites indicates that quiescent centrals have halo masses 0.3 dex larger than star-forming centrals, even when the stellar-mass distributions are fixed. We use a simple toy model that relates halo mass and quenching, which roughly reproduces the observed quenched fractions and the differences in halo mass between star-forming and quenched galaxies only if galaxies have a quenching probability that increases with halo mass from $\sim$0 for $\log(M_h/M_\odot)\sim$11 to $\sim$1 for $\log(M_h/M_\odot)\sim$13.5. A single halo-mass quenching threshold is unable to reproduce the quiescent fraction and satellite distribution of centrals. Therefore, while halo quenching may be an important mechanism, it is unlikely to be the only factor driving quenching. It remains unclear why a high fraction of centrals remain star-forming even in relatively massive halos.Comment: 19 pages, 17 figures, accepted by ApJ. Information on ZFOURGE can be found at http://zfourge.tamu.ed

The nature of the late achromatic bump in GRB 120326A

The long ${\it Swift}$ gamma-ray burst GRB 120326A at redshift $z=1.798$ exhibited a multi-band light curve with a striking feature: a late-time, long-lasting achromatic rebrightening, rarely seen in such events. Peaking in optical and X-ray bands $\sim 35$ ks ($\sim 12.5$ ks in the GRB rest frame) after the 70-s GRB prompt burst, the feature brightens nearly two orders of magnitude above the underlying optical power-law decay. Modelling the multiwavelength light curves, we investigate possible causes of the rebrightening in the context of the standard fireball model. We exclude a range of scenarios for the origin of this feature: reverse-shock flash, late-time forward shock peak due to the passage of the maximal synchrotron frequency through the optical band, late central engine optical/X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, that shapes the observed X-ray and optical light curves differently, ruling out a single overall emission component to explain the observed early time emission

Effect of local environment and stellar mass on galaxy quenching and morphology at 0.5<z<2.00.5<z<2.0

We study galactic star-formation activity as a function of environment and stellar mass over 0.5<z<2.0 using the FourStar Galaxy Evolution (ZFOURGE) survey. We estimate the galaxy environment using a Bayesian-motivated measure of the distance to the third nearest neighbor for galaxies to the stellar mass completeness of our survey, $\log(M/M_\odot)>9 (9.5)$ at z=1.3 (2.0). This method, when applied to a mock catalog with the photometric-redshift precision ($\sigma_z / (1+z) \lesssim 0.02$), recovers galaxies in low- and high-density environments accurately. We quantify the environmental quenching efficiency, and show that at z> 0.5 it depends on galaxy stellar mass, demonstrating that the effects of quenching related to (stellar) mass and environment are not separable. In high-density environments, the mass and environmental quenching efficiencies are comparable for massive galaxies ($\log (M/M_\odot)\gtrsim$ 10.5) at all redshifts. For lower mass galaxies ($\log (M/M)_\odot) \lesssim$ 10), the environmental quenching efficiency is very low at $z\gtrsim$ 1.5, but increases rapidly with decreasing redshift. Environmental quenching can account for nearly all quiescent lower mass galaxies ($\log(M/M_\odot) \sim$ 9-10), which appear primarily at $z\lesssim$ 1.0. The morphologies of lower mass quiescent galaxies are inconsistent with those expected of recently quenched star-forming galaxies. Some environmental process must transform the morphologies on similar timescales as the environmental quenching itself. The evolution of the environmental quenching favors models that combine gas starvation (as galaxies become satellites) with gas exhaustion through star-formation and outflows ("overconsumption"), and additional processes such as galaxy interactions, tidal stripping and disk fading to account for the morphological differences between the quiescent and star-forming galaxy populations.Comment: 29 pages, 15 figure, accepted for publication in Ap