118190331
RADIATION REACTION IN CURVED SPACETIME
27444996
Conservative, gravitational self-force for a particle in circular orbit around a Schwarzschild black hole in a radiation gauge
This is the second of two companion papers on computing the self-force in a radiation gauge; more precisely, the method uses a radiation gauge for the radiative part of the metric perturbation, together with an arbitrarily chosen gauge for the parts of the perturbation associated with changes in black-hole mass and spin and with a shift in the center of mass. In a test of the method delineated in the first paper, we compute the conservative part of the self-force for a particle in circular orbit around a Schwarzschild black hole. The gauge vector relating our radiation gauge to a Lorenz gauge is helically symmetric, implying that the quantity h_(αβ)u^(α)u^(β) must have the same value for our radiation gauge as for a Lorenz gauge; and we confirm this numerically to one part in 10^(14). As outlined in the first paper, the perturbed metric is constructed from a Hertz potential that is in a term obtained algebraically from the retarded perturbed spin-2 Weyl scalar, ψ_(0)^(ret). We use a mode-sum renormalization and find the renormalization coefficients by matching a series in L= l + 1/2 to the large-L behavior of the expression for the self-force in terms of the retarded field h_(αβ)^(ret); we similarly find the leading renormalization coefficients of h_(αβ)u^(α)u^(β) and the related change in the angular velocity of the particle due to its self-force. We show numerically that the singular part of the self-force has the form f^(S)_(α) = , the part of ∇_(α)ρ^(-1) that is axisymmetric about a radial line through the particle. This differs only by a constant from its form for a Lorenz gauge. It is because we do not use a radiation gauge to describe the change in black-hole mass that the singular part of the self-force has no singularity along a radial line through the particle and, at least in this example, is spherically symmetric to subleading order in ρ.
117312767
Light Higgs Scenario in BMSSM and LEP Precision Data
In this Letter we consider very light Higgs fields in BMSSM(Beyond MSSM). The spectrum below TeV scale is the same as the MSSM but the Higgs potential is modified and is well described in terms of effective dimension five and six operators. A correction from the BMSSM operators allows us to consider new parameter space of Higgs sector which is not allowed in the MSSM. It can be regarded as a constrained version of general 2 Higgs doublet model (2HDM) as long as Higgs sector is concerned. We focus on the possibility that CP odd Higgs (A) mass is about 7 or 8 GeV and charged Higgs mass is comparable to W mass. At the same time one of the CP even Higgs (h) is light enough such that h and A production at the Z pole is kinematically allowed. The tension between forward backward asymmetry of bottom quark Ab_FB measured at LEP and the Standard Model prediction can be ameliorated if bottom quark pair produced from light CP even Higgs is taken into account.
117044003
Parity violation in electron scattering from carbon: A progress report
An experiment is being performed at the MIT Bates Linear Accelerator Center to measure the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from Carbon. The asymmetry, which is due to the isoscalar component of the neutral weak current, is predicted to be about 0.6{times}10{sup {minus}6}. We have recently obtained preliminary data with polarized electrons. The status of the experiment is discussed.
59435944
UsingMT2to distinguish dark matter stabilization symmetries
We examine the potential of using colliders to distinguish models with parity (Z_2) stabilized dark matter (DM) from models in which the DM is stabilized by other symmetries, taking the latter to be a Z_3 symmetry for illustration. The key observation is that a heavier mother particle charged under a Z_3 stabilization symmetry can decay into one or two DM particles along with Standard Model (SM) particles. This can be contrasted with the decay of a mother particle charged under a parity symmetry; typically, only one DM particle appears in the decay chain. In arXiv:1003.0899, some of us studied the distributions of visible invariant mass from the decay of a single such mother particle in order to highlight the resulting distinctive signatures of Z_3 symmetry versus parity symmetry stabilized dark matter candidates. We now describe a complementary study which focuses on decay chains of the two mother particles which are necessarily present in these events. We also include in our analyss the missing energy/momentum in the event. For the Z_3 symmetry stabilized mothers, the resulting inclusive final state can have two, three or four DM particles. In contrast, models with Z_2 symmetry can have only two. We show that the shapes and edges of the distribution of M_T2-type variables, along with ratio of the visible momentum/energy on the two sides of the event, are powerful in distinguishing these different scenarios.
118406159
Distinguishing dark matter stabilization symmetries using multiple kinematic edges and cusps
We emphasize that the stabilizing symmetry for dark matter (DM) particles does not have to be the commonly used parity (Z{sub 2}) symmetry. We therefore examine the potential of the colliders to distinguish models with parity stabilized DM from models in which the DM is stabilized by other symmetries. We often take the latter to be a Z{sub 3} symmetry for illustration. We focus on signatures where a single particle, charged under the DM stabilization symmetry decays into the DM and standard model (SM) particles. Such a Z{sub 3}-charged mother particle can decay into one or two DM particles along with the same SM particles. This can be contrasted with the decay of a Z{sub 2}-charged mother particle, where only one DM particle appears. Thus, if the intermediate particles in these decay chains are off-shell, then the reconstructed invariant mass of the SM particles exhibits two kinematic edges for the Z{sub 3} case but only one for the Z{sub 2} case. For the case of on-shell intermediate particles, distinguishing the two symmetries requires more than the kinematic edges. In this case, we note that certain decay chain topologies of the mother particle which are present for the Z{sub 3} casemore » (but absent for the Z{sub 2} case) generate a cusp in the invariant mass distribution of the SM particles. We demonstrate that this cusp is generally invariant of the various spin configurations. We further apply these techniques within the context of explicit models.« less
119112331
W' in new physics models at the LHC
We study the new heavy charged gauge boson W' in various models including Left-Right symmetric, Little Higgs, Randall-Sundrum and universal extra dimension model considering pp \rightarrow W' \rightarrow lepton + neutrino with the 7 TeV and 14 TeV CM energies at the LHC. Of particular, we show that the universal extra dimension model is highly constrained by existing and forthcoming data.