SUSY Ward identities for multi-gluon helicity amplitudes with massive quarks

We use supersymmetric Ward identities to relate multi-gluon helicity amplitudes involving a pair of massive quarks to amplitudes with massive scalars. This allows to use the recent results for scalar amplitudes with an arbitrary number of gluons obtained by on-shell recursion relations to obtain scattering amplitudes involving top quarks.Comment: 22 pages, references adde

On-shell supersymmetry for massive multiplets

The consequences of on-shell supersymmetry are studied for scattering amplitudes with massive particles in four dimensions. Using the massive version of the spinor helicity formalism the supersymmetry transformations relating products of on-shell states are derived directly from the on-shell supersymmetry algebra for any massive representation. Solutions to the resulting Ward identities can be constructed as functions on the on-shell superspaces that are obtained from the coherent state method. In simple cases it is shown that these superspaces allow one to construct explicitly supersymmetric scattering amplitudes. Supersymmetric on-shell recursion relations for tree-level superamplitudes with massive particles are introduced. As examples, simple supersymmetric amplitudes are constructed in SQCD, the Abelian Higgs model, the Coulomb branch of N=4 super Yang-Mills, QCD with an effective Higgs-gluon coupling and for massive vector boson currents.Comment: 49+9 pages, 4 figures, v2: references updated, typos corrected, examples added, v3: final PRD versio

High precision fundamental constants at the TeV scale

This report summarizes the proceedings of the 2014 Mainz Institute for Theoretical Physics (MITP) scientific program on "High precision fundamental constants at the TeV scale". The two outstanding parameters in the Standard Model dealt with during the MITP scientific program are the strong coupling constant $\alpha_s$ and the top-quark mass $m_t$. Lacking knowledge on the value of those fundamental constants is often the limiting factor in the accuracy of theoretical predictions. The current status on $\alpha_s$ and $m_t$ has been reviewed and directions for future research have been identified.Comment: 57 pages, 24 figures, pdflate

Fast Stochastic Cooling of Heavy Ions at the ESR Storage Ring

Since the completion of the installation of pick-up and kicker tanks in the ESR, stochastic cooling in all phase space dimensions has been demonstrated with rather short cooling times. New RF components were added. The system is now ready for experiments with secondary beams. The momentum sensitivity of the pick-up electrodes was measured. The ability of the Palmer cooling system to cool beams with a maximum momentum spread of ± 0.7 % was demonstrated. After injecting an uncooled primary argon beam from the SIS synchrotron, e-folding cooling times of 0.86 s in the longitudinal phase plane and 1.6 s in the horizontal plane were measured with 5×106 injected particles. These values are close to theoretical expectations. In a first experiment with uranium, the shortest cooling times have been below 0.5 s in both the longitudinal and vertical phase planes. The system cools the complete injected beam without beam loss. An experiment with beam accumulation following stochastic precooling was performed successfully. The resulting equilibrium phase space densities are high enough to be followed by fast electron cooling of the stack

Stochastic Cooling at the ESR

Stochastic precooling at the ESR storage ring of GSI will be used mainly for experiments with stored radioactive fragment beams. They arrive from the fragment separator with momentum spreads and emittances for which electron cooling is too slow. The installation of components at the ESR is now complete and first commissioning experiments have been performed. Both longitudinal and transverse stochastic cooling have been demonstrated. The paper gives a short account of the system architecture, and of the response of quarter-wave plates and superelectrodes at intermediate energies. The preparation of fragment beams suitable for subsequent electron cooling is discussed for the case that a mixture of different ion species is present in the cooler ring. Results of commissioning and future prospects are presented

Unitarity, BRST Symmetry and Ward Identities in Orbifold Gauge Theories

We discuss the use of BRST symmetry and the resulting Ward identities for orbifold gauge theories as consistency checks in an arbitrary number of dimensions. We verify that both the usual orbifold symmetry breaking and the recently proposed Higgsless symmetry breaking are consistent with the nilpotency of the BRST transformation. Imposing the Ward identities resulting from the BRST symmetry on the 4-point functions of theory, we obtain relations on the coupling constants that are shown to be equivalent to the conditions for tree level unitarity. We present the complete set of these sum rules also for inelastic scattering and discuss applications to 6-dimensional models and to incomplete matter multiplets on orbifold fixed points.Comment: 34 pages, LaTeX (feynmf.sty, url.sty and thophys.sty included), v2:references added, v3:typos corrected, sec.3 revise

Multigluon tree amplitudes with a pair of massive fermions

We consider the calculation of n-point multigluon tree amplitudes with a pair of massive fermions in QCD. We give the explicit transformation rules of this kind of massive fermion-pair amplitudes with respect to different reference momenta and check the correctness of them by SUSY Ward identities. Using these rules and onshell BCFW recursion relation, we calculate the analytic results of several n-point multigluon amplitudes.Comment: 15page

A direct proof of the CSW rules

Using recursion methods similar to those of Britto, Cachazo, Feng and Witten (BCFW) a direct proof of the CSW rules for computing tree-level gluon amplitudes is given.Comment: 11 pages, uses axodraw.st

Massive amplitudes on the Coulomb branch of N=4 SYM

We initiate a systematic study of amplitudes with massive external particles on the Coulomb-branch of N=4 super Yang Mills theory: 1) We propose that (multi-)soft-scalar limits of massless amplitudes at the origin of moduli space can be used to determine Coulomb-branch amplitudes to leading order in the mass. This is demonstrated in numerous examples. 2) We find compact explicit expressions for several towers of tree-level amplitudes, including scattering of two massive W-bosons with any number of positive helicity gluons, valid for all values of the mass. 3) We present the general structure of superamplitudes on the Coulomb branch. For example, the n-point "MHV-band" superamplitude is proportional to a Grassmann polynomial of mixed degree 4 to 12, which is uniquely determined by supersymmetry. We find explicit tree-level superamplitudes for this MHV band and for other simple sectors of the theory. 4) Dual conformal generators are constructed, and we explore the dual conformal properties of the simplest massive amplitudes. Our compact expressions for amplitudes and superamplitudes should be of both theoretical and phenomenological interest; in particular the tree-level results carry over to truncations of the theory with less supersymmetry.Comment: 29 pages, 1 figur