Integrating out new fermions at one loop

We present the fermionic universal one-loop effective action obtained by integrating out heavy vector-like fermions at one loop using functional techniques. Even though previous approaches are able to handle integrating out heavy fermions with non-chiral interactions, i.e. vanishing γ5 interaction terms, the computations proceed in a tedious manner that obscures a physical interpretation. We show how directly tackling the fermionic functional determinant not only allows for a much simpler and transparent computation, but is also able to account for chiral interaction terms in a simple, algorithmic way. Finally, we apply the obtained results to integrate out at one loop the vector-like fermions appearing in a toy model and in a fermionic model that exhibits strong cosmological phase transitions

Integrating Out New Fermions at One Loop

We present the fermionic universal one--loop effective action obtained by integrating out heavy vector--like fermions at one loop using functional techniques. Even though previous approaches are able to handle integrating out heavy fermions with non--chiral interactions, i.e. vanishing $\gamma^5$ interaction terms, the computations proceed in a tedious manner that obscures a physical interpretation. We show how directly tackling the fermionic functional determinant not only allows for a much simpler and transparent computation, but is also able to account for chiral interaction terms in a simple, algorithmic way. Finally, we apply the obtained results to integrate out at one loop the vector--like fermions appearing in a toy model and in a fermionic model that exhibits strong cosmological phase transitions.Comment: 36 pages, no figure

Hollow cone sieve for top

A method of top tagging is introduced. Using the anti-kt algorithm to define jets, events with nj = 2 fat jets of cone size R = 1.5 are decomposed into R = 0.6 subjets and retained if nj (R = 0.6) [?] 4. One pair of subjets reconstructs the W mass and another two subjets are tagged as a b-jet, as necessary for hadronic or semileptonic events of tt origin. This “hollow cone” method distinguishes the tt events from the light parton QCD dijet events. Our simulations are made for the LHC at 7 TeV. The sieve allows for top identification at lower pT than other proposed methods and thus allows a higher signal retention

Higgs boson finder and mass estimator: The Higgs boson to WW to leptons decay channel at the LHC

We exploit the spin and kinematic correlations in the decay of a scalar boson into a pair of real or virtual W-bosons, with both W-bosons decaying leptonically, for Higgs boson discovery at 7 TeV LHC energy with 10 fb-1 luminosity. Without reconstruction of the events, we obtain estimators of the Higgs mass from the peak and width of the signal distribution in mll. The separation of signal and background with other distributions, such as the azimuthal angle between two W decay planes, the rapidity difference between the two leptons, missing ET, and the pT of leptons, are also prescribed. Our approach identifies the salient Higgs to dilepton signatures that allow subtraction of the continuum W * W * background

Leptogenesis triggered by a first-order phase transition

We propose a new scenario of leptogenesis, which is triggered by a first-order phase transition (FOPT). The right-handed neutrinos (RHNs) are massless in the old vacuum, while they acquire a mass in the new vacuum bubbles, and the mass gap is huge compared with the FOPT temperature. The ultra-relativistic bubble walls sweep the RHNs into the bubbles, where the RHNs experience fast decay and generate the lepton asymmetry, which is further converted to the baryon asymmetry of the Universe (BAU). Since the RHNs are out of equilibrium inside the bubble, the generated BAU does not suffer from the thermal bath washout. We first discuss the general feature of such a FOPT leptogenesis mechanism, and then realize it in an extended B−L model. The gravitational waves from U(1)B−L breaking could be detected at the future interferometers

Scalar-Top Masses from SUSY Loops with 125 GeV mh and precise Mw, mt

We constrain the masses of scalar-tops (stop) by analyzing the new precision Tevatron measurement of the W-boson mass and the LHC/Tevatron indications of a Higgs boson of mass 125.5+-1 GeV. Our study adopts Natural SUSY with low fine-tuning, which has multi-TeV first and second generation squarks and a light Higgsino mixing parameter mu=150 GeV. An effective Lagrangian calculation is made of mh to 3-loops using the H3m program with weak scale SUSY parameters obtained from RGE evolution from the GUT scale in the Natural SUSY scenario. The SUSY radiative corrections to the Higgs mass imply maximal off-diagonal elements of the stop mass-matrix and a mass splitting of the two stops larger than 400 GeV.Comment: 18 pages, 5 figures, Phys. Lett. B 718 (2013) 1024-103

Corrections to di-Higgs boson production with light stops and modified Higgs couplings

The Higgs pair production in gluon fusion is a sensitive probe of beyond-Standard Model (BSM) phenomena and its detection is a major goal for the LHC and higher energy hadron collider experiments. In this work we reanalyze the possible modifications of the Higgs pair production cross section within low energy supersymmetry models. We show that the supersymmetric contributions to the Higgs pair production cross section are strongly correlated with the ones of the single Higgs production in the gluon fusion channel. Motivated by the analysis of ATLAS and CMS Higgs production data, we show that the scalar superpartners' contributions may lead to significant modification of the di-Higgs production rate and invariant mass distribution with respect to the SM predictions. We also analyze the combined effects on the di-Higgs production rate of a modification of the Higgs trilinear and top-quark Yukawa couplings in the presence of light stops. In particular, we show that due to the destructive interference of the triangle and box amplitude contributions to the di-Higgs production cross section, even a small modification of the top-quark Yukawa coupling can lead to a significant increase of the di-Higgs production rate.Comment: 33 pages, 13 figures v2: minor improvements, PRD versio