119097432
The light stop window
We show that a right-handed stop in the 200–400 GeV mass range, together with a nearly degenerate neutralino and, possibly, a gluino below 1.5 TeV, follows from reasonable assumptions, is consistent with present data, and offers interesting discovery prospects at the LHC. Triggering on an extra jet produced in association with stops allows the experimental search for stops even when their mass difference with neutralinos is very small and the decay products are too soft for direct observation. Using a razor analysis, we are able to set stop bounds that are stronger than those published by ATLAS and CMS.
119271031
Phenomenology of a lepton triplet
The most general phenomenological model involving a lepton triplet with hypercharge ±1 is constructed. A distinctive feature of this model is the predict ion of a doubly charged lepton, and a new heavy Dirac neutrino. We study the phenomenology of these exotic leptons in both low-energy experiments and at the LHC. The model predicts FCNC processes such as muon and tau rare decays, which are studied in detail in order to constrain the model pa rameters. All the decay channels of the exotic leptons are described for a wide range of parameters. It is found that, if the mixing parameters between the exotic and light leptons are not too small (> 10 6 ), then they can be observable to a 3 − 5σ statistical significance at the 7 TeV LHC with 10 − 50 fb 1 luminosity for a 400 GeV mass, and 14 TeV with100 − 300 fb 1 luminosity for a 800 GeV mass.
119113677
Cornering a hyper Higgs boson: Angular kinematics for boosted Higgs bosons with top pairs
In the wake of the Higgs discovery and over the long haul of the LHC run, one should keep a lookout for kinematic anomalies in the most massive known trio of coupled particles, $t \bar{t} h$. After surveying the scope of prior constraints on chromomagnetic dipole and Higgs-gluon kinetic couplings, we focus on surpluses of boosted-$p_T$ Higgs bosons fomented by these momentum dependent dimension-six operators in $t \bar{t} h$ final states. We uncover a number of simple, $p_T$ weighted angular variables useful for discriminating Standard Model from dimension-6 boosted Higgs distributions, and make headway arguing that one of these variables may improve the reach of existing Standard Model top-Higgs searches. The approach we take is model independent, because we just consider a set of effective operators that contribute to the same three-body final state.
118980897
Two-loop Higgs mass in supersymmetric Kaluza-Klein theories
We perform an explicit two-loop computation of the Higgs mass in a five-dimensional supersymmetric theory compactified on the orbifold S^1/Z_2, with superpotential localized on a fixed-point brane and supersymmetry broken in the bulk of the extra dimension by Scherk-Schwarz boundary conditions. At one-loop, the Higgs mass is finite and proportional to 1/R^2, R being the radius of the extra dimension. The two-loop corrections contain finite proportional to 1/R^2 and linearly divergent Lambda/R terms, where Lambda is the cutoff of the five-dimensional theory. The divergent terms are cancelled by diagrams containing one-loop wave-function renormalization counterterms, i.e. by linear threshold effects of Yukawa (and gauge) couplings, at the scale 1/R. As a result there is no counterterm for the Higgs mass, which is finite and calculable to the considered order.
17491984
Note on unparticle decays
The coupling of an unparticle operator O{sub U} to standard model particles opens up the possibility of unparticle decays into standard model fields. We study this issue by analyzing the pole structure (and spectral function) of the unparticle propagator, corrected to account for one-loop polarization effects from virtual standard model particles. We find that the propagator of a scalar unparticle (of scaling dimension 1{<=}d{sub U}<2) with a mass gap m{sub g} develops an isolated pole, m{sub p}{sup 2}-im{sub p}{gamma}{sub p}, with m{sub p}{sup 2} < or approx. m{sub g}{sup 2} below the unparticle continuum that extends above m{sub g} (showing that the theory would be unstable without a mass gap). If that pole lies below the threshold for decay into two standard model particles, it corresponds to a stable unparticle state (and its width {gamma}{sub p} is zero). For m{sub p}{sup 2} above the threshold, the width is nonzero and related to the rate of the unparticle decay into standard model particles. This picture is valid for any value of d{sub U} in the considered range.
15511076
Gauge coupling renormalization in RS1
Abstract We compute the 4D low energy effective gauge coupling at one-loop order in the compact Randall–Sundrum scenario with bulk gauge fields and charged matter, within controlled approximations. While such computations are subtle, they can be important for studying phenomenological issues such as grand unification. Ultraviolet divergences are cut-off using Pauli–Villars regularization so as to respect 5D gauge and general coordinate invariance. The structure of these divergences on branes and in the bulk is elucidated by a 5D position-space analysis. The remaining finite contributions are obtained by a careful analysis of the Kaluza–Klein spectrum. We comment on the agreement between our results and expectations based on the AdS/CFT correspondence, in particular logarithmic sensitivity to the 4D Planck scale.
119019620
Pre-main sequence stars in open clusters - I. The DAY-I catalogue
Context. We present the basic ideas and first results from the project we are carrying out at present, the search for and characterisation of pre-main sequence (PMS) stars among the members of Galactic young clusters. The observations of 10 southern clusters, nine of them located in the Carina-Sagittarius spiral arm of the Milky Way are presented. Aims. We aim at listing candidate PMS member stars in young clusters. The catalogued stars will serve as a basis for future spectroscopic studies of individual objects to determine the properties of stellar formation in the last phases before the main sequence stage. Properties such as the presence of residual envelopes or disks, age spread among PMS members, and the possible presence of several episodes of star formation in the clusters, are to be addressed. Methods. Multicolour photometry in the $UBVR_{\rm C}I_{\rm C}$ system has been obtained for 10 southern young clusters in the fourth Galactic quadrant, located between Galactic longitudes l = 238° and l = 310°. For six clusters in the sample, the observations presented here provide the first published study based on CCD photometry. A quantitative comparison is performed with post-MS isochrones, and PMS isochrones from three different evolutionary models are used in the photometric membership analysis for possible PMS stars. Results. The observations produce photometric indices in the Johnson-Cousins photometric systems for a total of 26 962 stars. The matching of our pixel coordinates with corresponding fields in the 2MASS data base provides astrometric calibration for all cataloged stars and JHK 2MASS photometric indices for 60% of them. Post-MS cluster ages range from 4 to 60 Myr, whereas the photometric membership analysis assigns PMS membership to a total of 842 stars, covering an age range between 1 and 10 Myr. This information on the PMS candidate members has been collected into a catalogue, named DAY-I, which contains 16 entries for 842 stars in the field of 10 southern clusters.
15082396
Multiwavelength Analysis of the Young Open Cluster NGC 2362
We present a multiwavelength analysis of the young open cluster NGC 2362; UBVRCIC CCD photometric observations, together with available data in the Chandra database, near-infrared data from the Two Micron All Sky Survey (2MASS), and recently published Hα spectroscopy were used to get information about the evolutionary stage of the cluster and the main physical properties of its stellar content. Cluster membership is estimated for every individual star by means of zero-age main sequence (ZAMS) and isochrone fitting. The cluster is confirmed to host a rich population of pre-main-sequence (PMS) objects and to contain a large number of X-ray-emitting stars, which reach from the PMS members of GK spectral type up to the most luminous OB main-sequence (MS) members. The PMS cluster members show no significant age spread, and the comparison to both PMS and post-MS isochrones suggests an homogeneous age for all cluster members. The analysis allows us to assess the validity of currently used PMS evolutionary models and supports the suggestion of a well-defined positive correlation of the X-ray emission from PMS stars with their bolometric luminosity. Clear differences are found between the X-ray activity properties of MS and PMS cluster members, both in the relation between X-ray luminosity and bolometric luminosity, and in spectral properties as well.
16422495
A young double stellar cluster in a HII region, emerging from its parent molecular cloud ⋆
Aims. We investigate the star formation occurring in the region towards IRAS 07141-0920 contained in the HII region Sh2-294 (S294). We report the discovery ��� of a new young double stellar cluster, and we describe its properties. Methods. High-resolution optical UBVRI and Hα images obtained with ALFOSC mounted on the Nordic Optical Telescope (NOT), near-infrared JHKS images obtained with NOTCam at the Nordic Optical Telescope, and VLT/ISAAC images obtained through the H2 (2.12 µm) filter were all used to make photometric and morphological studies of the point sources and the nebula seen towards Sh2-294. Identification of PMS members was done using three different methods: comparison with isochrones in optical colour−magnitude diagrams and detection of either near-IR excess or Hα emission. Results. The optical images reveal an emission nebula rich in morphological details. The nebula is composed mainly of ultraviolet scattered light and of Hα emission with local morphological features conveying an impression of strong dynamical complexity. Contrasting with the bright parts of the nebula, opaque patches are seen. They appear elongated, filamentary, or clumpy. Our optical photometry confirms that the identification of the illuminator of the nebula is likely to be a B0.5V star located at a distance of about 3.2 kpc. Our high-resolution near-IR images reveal an embedded cluster, extending about 2 pc and exhibiting sub-clustering: a denser, more condensed, subcluster surrounding the optical high-mass B0.5V illuminator star; and a more embedded, optically invisible, subcluster located towards the eastern, dark part of the nebula and including the luminous MSX source G224.1880+01.2407, a massive protostellar candidate that could be the origin of jets and extended features seen at 2.12 µm. The double cluster appears to be clearing the remaining molecular material of the parent cloud, creating patches of lower extinction and allowing some of the least reddened members to be detected in the optical images. We find 12 main-sequence (MS) and 143 pre-main sequence(PMS) members. The most massive star fits a 4 Myr, post-MS isochrone. The age of the optically selected PMS population is estimated to be 7− 8M yr. The IR-excess population shows sub-clustering on scales as small as 0.23 pc and is probably much younger.