73681918
Yukawa corrections to Higgs production in top partner models
Higgs production from gluon fusion is sensitive to the properties of heavy colored fermions and to the Yukawa couplings, YFMF v , of these particles to the Higgs boson. We compute the two–loop, O � � YFMF v � 3 � contributions of new high mass fermions to Higgs production. In the Standard Model, these contributions are part of the well-known electroweak corrections and are negligible. However, in models with TeV scale fermions, such as top partner or composite models, Yukawa corrections are enhanced by effects of O � � YFMF v � 3 � and are potentially significant due to the large mass of the new quarks. We examine the size of these top partner Yukawa corrections to Higgs production for parameter choices which are allowed by precision electroweak constraints.
118631641
Higgs production cross-section in a Standard Model with four generations at the LHC
We present theoretical predictions for the Higgs boson production cross-section via gluon fusion at the LHC in a Standard Model with four generations. We include QCD corrections through NLO retaining the full dependence on the quark masses, and the NNLO corrections in the heavy quark effective theory approximation. We also include electroweak corrections through three loops. Electroweak and bottom-quark contributions are suppressed in comparison to the Standard Model with three generations.
118582742
Discovery potential of top-partners in a realistic composite Higgs model with early LHC data
Composite Higgs models provide a natural, non-supersymmetric solution to the hierarchy problem. In these models, one or more sets of heavy top-partners are typically introduced. Some of these new quarks can be relatively light, with a mass of a few hundred GeV, and could be observed with the early LHC collision data expected to be collected during 2010. We analyse in detail the collider signatures that these new quarks can produce. We show that final states with two (same-sign) or three leptons are the most promising discovery channels. They can yield a 5σ excess over the Standard Model expectation already with the 2010 LHC collision data. Exotic quarks of charge 5/3 are a distinctive feature of this model. We present a new method to reconstruct their masses from their leptonic decay without relying on jets in the final state.
53117738
Higgs boson gluon–fusion production at threshold in N3LO QCD
We present the cross-section for the threshold production of the Higgs boson at hadron-colliders at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. We present an analytic expression for the partonic cross-section at threshold and the impact of these corrections on the numerical estimates for the hadronic cross-section at the LHC. With this result we achieve a major milestone towards a complete evaluation of the cross-section at N3LO which will reduce the theoretical uncertainty in the determination of the strengths of the Higgs boson interactions.
119628433
-symmetric extension of the Korteweg-de Vries equation
The Korteweg-de Vries equation ut + uux + uxxx = 0 is symmetric (invariant under spacetime reflection). Therefore, it can be generalized and extended into the complex domain in such a way as to preserve the symmetry. The result is the family of complex nonlinear wave equations ut − iu(iux) + uxxx = 0, where is real. The features of these equations are discussed. Special attention is given to the = 3 equation, for which conservation laws are derived and solitary waves are investigated.
119117508
Gluon-fusion Higgs production at NNLO for a non-standard Higgs sector
We consider an extension of the Standard Model with an arbitrary number of heavy quarks having general couplings to the Higgs boson. We construct an effective Lagrangian integrating out quarks that are heavier than half the mass of the Higgs boson and compute the Wilson coefficient for the effective gluon-Higgs vertex through NNLO. We apply our result to a composite Higgs model with vector-like quarks coupling to the third generation quarks. In the heavy quark-mass approximation, we show that the suppression of the leading-order cross section with respect to the Standard Model does not depend on the number of vector-like multiplets introduced. We analyse the effects of QCD and electroweak corrections through three loops, as well as bottom-quark contributions through two loops.
117890277
Properties and evolution of circumstellar disks and envelopes around young low-mass stars in the Taurus star-forming region
18267720
Spitzer IRS Spectra and Envelope Models of Class I Protostars in Taurus
We present Spitzer Infrared Spectrograph (IRS) spectra of 28 Class I protostars in the Taurus star-forming region. The 5-36 μm spectra reveal excess emission from the inner regions of the envelope and accretion disk surrounding these predecessors of low-mass stars, as well as absorption features due to silicates and ices. Together with shorter and longer wavelength data from the literature, we construct spectral energy distributions and fit envelope models to 22 protostars of our sample, most of which are well constrained due to the availability of the IRS spectra. We infer that the envelopes of the Class I objects in our sample cover a wide range in parameter space, particularly in density and centrifugal radius, implying different initial conditions for the collapse of protostellar cores.
119302415
SPITZER SPECTROSCOPY OF THE CIRCUMPRIMARY DISK IN THE BINARY BROWN DWARF 2MASS J04414489+2301513*
Using the Spitzer Infrared Spectrograph, we have performed mid-infrared spectroscopy on the young binary brown dwarf 2MASS J04414489+2301513 (15 AU) in the Taurus star-forming region. The spectrum exhibits excess continuum emission that likely arises from a circumstellar disk around the primary. Silicate emission is not detected in these data, indicating the presence of significant grain growth. This is one of the few brown dwarf disks at such a young age (~1 Myr) that has been found to lack silicate emission. To quantitatively constrain the properties of the disk, we have compared the spectral energy distribution of 2MASS J04414489+2301513 to the predictions of our vertical structure codes for irradiated accretion disks. Our models suggest that the remaining atmospheric grains of moderately depleted layers may have grown to a size of 5 μm. In addition, our model fits indicate an outer radius of 0.2-0.3 AU for the disk. The small size of this circumprimary disk could be due to truncation by the secondary. The absence of an outer disk containing a reservoir of small, primordial grains, combined with a weak turbulent mechanism, may be responsible for the advanced grain growth in this disk.
16702552
Predicted colors and flux densities of protostars in the Herschel PACS and SPIRE filters
Upcoming surveys with the Herschel Space Observatory will yield far-IR photometry of large samples of young stellar objects, which will require careful interpretation. We investigate the color and luminosity diagnostics based on Herschel broad-band filters to identify and discern the properties of low-mass protostars. We compute a grid of 2016 protostars in various physical congurations, present the expected flux densities and flux density ratios for this grid of protostars, and compare Herschel observations of three protostars to the model results. These provide useful constraints on the range of colors and fluxes of protostar in the Herschel filters. We find that Herschel data alone is likely a useful diagnostic of the envelope properties of young stars.
36459586
The State of Protoplanetary Material 10 Million years after Stellar Formation: Circumstellar Disks in the TW Hydrae Association
We have used the Spitzer Space Telescope Infrared Spectrograph to observe seven members of the TW Hya association, the nearest stellar association whose age (~10 Myr) is similar to the timescales thought to apply to planet formation and disk dissipation. Only two of the seven targets display infrared excess emission, indicating that substantial amounts of dust still exist closer to the stars than is characteristic of debris disks; however, in both objects we confirm an abrupt short-wavelength edge to the excess, as is seen in disks with cleared-out central regions. The mid-infrared excesses in the spectra of Hen 3-600 and TW Hya include crystalline silicate emission features, indicating that the grains have undergone significant thermal processing. We offer a detailed comparison between the spectra of TW Hya and Hen 3-600, and a model that corroborates the spectral shape and our previous understanding of the radial structure of these protoplanetary disks.