54 research outputs found
The Higgs Decay Width in Multi-Scalar Doublet Models
We show that there are regions of parameter space in multi-scalar doublet
models where, in the first few hundred inverse femtobarns of data, the new
charged and neutral scalars are not directly observable at the LHC and yet the
Higgs decay rate to b bbar is changed significantly from its standard model
value. For a light Higgs with a mass less than 140 GeV, this can cause a large
change in the number of two photon and tau tau Higgs decay events expected at
the LHC compared to the minimal standard model. In the models we consider, the
principle of minimal flavor violation is used to suppress flavor changing
neutral currents. This paper emphasizes the importance of measuring the
properties of the Higgs boson at the LHC; for a range of parameters the model
considered has new physics at the TeV scale that is invisible, in the first few
hundred inverse femtobarns of integrated luminosity at the LHC, except
indirectly through the measurement of Higgs boson properties.Comment: 18 pages, 3 figures V2: refs adde
Factorization and the Soft-Collinear Effective Theory: Color-Suppressed Decays
We discuss the soft-collinear effective theory (SCET) and kinematic
expansions in B-decays, focusing on recent results for color suppressed B ->
D^(*) X decays. In particular we discuss model independent predictions for B^0
-> D^0 pi^0 and B^0 -> D^*0 pi^0, and update the comparison using new
experimental data. We show why HQET alone is insufficient to give these
results. SCET predictions are also reviewed for other B and Lambda_b decay
channels that are not yet tested by data.Comment: 5 pages, plenary talk given by I.S. at Beauty 200
The Higgs Decay Width in Multi-Scalar Doublet Models
We show that there are regions of parameter space in multi-scalar doublet
models where, in the first few hundred inverse femtobarns of data, the new
charged and neutral scalars are not directly observable at the LHC and yet the
Higgs decay rate to b bbar is changed significantly from its standard model
value. For a light Higgs with a mass less than 140 GeV, this can cause a large
change in the number of two photon and tau tau Higgs decay events expected at
the LHC compared to the minimal standard model. In the models we consider, the
principle of minimal flavor violation is used to suppress flavor changing
neutral currents. This paper emphasizes the importance of measuring the
properties of the Higgs boson at the LHC; for a range of parameters the model
considered has new physics at the TeV scale that is invisible, in the first few
hundred inverse femtobarns of integrated luminosity at the LHC, except
indirectly through the measurement of Higgs boson properties.Comment: 18 pages, 3 figures V2: refs adde
Transverse Momentum Distributions from Effective Field Theory
We review a new approach to calculating transverse momentum distributions of
the Higgs and electroweak gauge bosons using the Soft-Collinear Effective
Theory. We derive a factorization theorem for transverse momentum distributions
in terms of newly-defined impact-parameter beam functions (iBFs) and an inverse
soft function (iSF). The iBFs correspond to completely unintegrated parton
distribution functions and provide interesting probes of momentum distributions
within nucleons. The numerical matching between the low and high transverse
momentum regions is improved in this approach with respect to standard
techniques. We present results for next-to-leading logarithmic resummation for
the Higgs and Z-boson distributions and give a comparison with Tevatron data.Comment: 9 pages, 3 figures, Invited Talk presented at the workshop on "QCD
Evolution of Parton Distributions: from Collinear to Non-collinear Case",
April 8th-9th, 2011, Thomas Jefferson National Accelerator Facilit
New Physics Effects in Higgs Decay to Tau Leptons
We study the possible effects of TeV scale new physics (NP) on the rate for
Higgs boson decays to charged leptons, focusing on the tau tau channel which
can be readily studied at the Large Hadron collider. Using an SU(3)_C X SU(2)_L
X U(1)_Y invariant effective theory valid below a NP scale Lambda, we determine
all effective operators up to dimension six that could generate appreciable
contributions to the decay rate and compute the dependence of the rate on the
corresponding operator coefficients. We bound the size of these operator
coefficients based on the scale of the tau mass, naturalness considerations,
and experimental constraints on the tau anomalous magnetic moment. These
considerations imply that contributions to the decay rate from a NP scale
Lambda ~ TeV could be comparable to the prediction based on the SM Yukawa
interaction. A reliable test of the Higgs mechanism for fermion mass generation
via the h-> tau tau channel is possible only after such NP effects are
understood and brought under theoretical control.Comment: 10 pages, 6 figures, V2: typos correcte
Implications of a scalar dark force for terrestrial experiments
A long-range intergalactic force between dark matter (DM) particles, mediated by an ultralight scalar, is tightly constrained by galactic dynamics and large scale structure formation. We examine the implications of such a ‘‘dark force” for several terrestrial experiments, including Eötvös tests of the Weak Equivalence Principle (WEP), direct-detection DM searches, and collider studies. The presence of a dark force implies a nonvanishing effect in Eötvös tests that could be probed by current and future experiments depending on the DM model. For scalar DM that is a singlet under the standard model gauge groups, a dark force of astrophysically relevant magnitude is ruled out in large regions of parameter space by the DM relic density and WEP constraints. WEP tests also imply constraints on the Higgs-exchange contributions to the spin-independent (SI) DM-nucleus direct-detection cross section. For WIMP scenarios, these considerations constrain Higgs-exchange contributions to the SI cross section to be subleading compared to gauge-boson mediated contributions. In multicomponent DM scenarios, a dark force would preclude large shifts in the rate for Higgs decay to two photons associated with DM-multiplet loops that might otherwise lead to measurable deviations at the LHC or a future linear collider. The combination of observations from galactic dynamics, large scale structure formation, Eötvös experiments, DM-direct-detection experiments, and colliders can further constrain the size of new long-range forces in the dark sector
- …