14 research outputs found
Flavored dark matter beyond Minimal Flavor Violation
We study the interplay of flavor and dark matter phenomenology for models of
flavored dark matter interacting with quarks. We allow an arbitrary flavor
structure in the coupling of dark matter with quarks. This coupling is assumed
to be the only new source of violation of the Standard Model flavor symmetry
extended by a associated with the dark matter. We call this ansatz
Dark Minimal Flavor Violation (DMFV) and highlight its various implications,
including an unbroken discrete symmetry that can stabilize the dark matter. As
an illustration we study a Dirac fermionic dark matter which transforms
as triplet under , and is a singlet under the Standard Model. The
dark matter couples to right-handed down-type quarks via a colored scalar
mediator with a coupling . We identify a number of
"flavor-safe" scenarios for the structure of which are beyond Minimal
Flavor Violation. For dark matter and collider phenomenology we focus on the
well-motivated case of -flavored dark matter. The combined flavor and dark
matter constraints on the parameter space of turn out to be
interesting intersections of the individual ones. LHC constraints on simplified
models of squarks and sbottoms can be adapted to our case, and monojet searches
can be relevant if the spectrum is compressed.Comment: 40 pages, 19 figures, 3 tables. Clarifying comments and some
references added, matches published versio
Rare K and B Decays in a Warped Extra Dimension with Custodial Protection
We present a complete study of rare K and B meson decays in a warped extra
dimensional model with a custodial protection of (both diagonal and
non-diagonal) Z d_L^i \bar d_L^j couplings, including K^+ -> pi^+ nu anti-nu,
K_L -> pi^0 nu anti-nu, K_L -> pi^0 l^+ l^-, K_L -> mu^+ mu^-, B_{s,d} -> mu^+
mu^-, B -> K nu anti-nu, B -> K^* nu anti-nu and B -> X_{s,d} nu anti-nu. In
this model in addition to Standard Model one loop contributions these processes
receive tree level contributions from the Z boson and the new heavy electroweak
gauge bosons. We analyse all these contributions that turn out to be dominated
by tree level Z boson exchanges governed by right-handed couplings to down-type
quarks. Imposing all existing constraints from Delta F=2 transitions analysed
by us recently and fitting all quark masses and CKM mixing parameters we find
that a number of branching ratios for rare K decays can differ significantly
from the SM predictions, while the corresponding effects in rare B decays are
modest, dominantly due to the custodial protection being more effective in B
decays than in K decays. In order to reduce the parameter dependence we study
correlations between various observables within the K system, within the B
system and in particular between K and B systems, and also between Delta F=2
and Delta F=1 observables. These correlations allow for a clear distinction
between this new physics scenario and models with minimal flavour violation or
the Littlest Higgs Model with T-parity, and could give an opportunity to future
experiments to confirm or rule out the model. We show how our results would
change if the custodial protection of Z d_L^i bar d^j_L couplings was absent.
In the case of rare B decays the modifications are spectacular.Comment: 50 pages, 17 figures. v2: minor clarifying comments and references
added. v3: few clarifying comments added, matches published versio
Quark flavour mixing with right-handed currents: an effective theory approach
The impact of right-handed currents in both charged- and neutral-current
flavour-violating processes is analysed by means of an effective theory
approach. More explicitly, we analyse the structure of dimension-six operators
assuming a left-right symmetric flavour group, commuting with an underlying
global symmetry, broken only by two
Yukawa couplings. The model contains a new unitary matrix controlling
flavour-mixing in the right-handed sector. We determine the structure of this
matrix by charged-current data, where the tension between inclusive and
exclusive determinations of can be solved. Having determined the
size and the flavour structure of right-handed currents, we investigate how
they would manifest themselves in neutral current processes, including
particle-antiparticle mixing, , , , and decays. The possibility to
explain a non-standard CP-violating phase in mixing in this context, and
the comparison with other predictive new-physics frameworks addressing the same
problem, is also discussed. While a large asymmetry can easily
be accommodated, we point out a tension in this framework between
and .Comment: 39 pages, 3 fig
Electroweak and Flavour Structure of a Warped Extra Dimension with Custodial Protection
We present the electroweak and flavour structure of a model with a warped
extra dimension and the bulk gauge group SU(3) x SU(2)_L x SU(2)_R x P_LR x
U(1)_X. The presence of SU(2)_R implies an unbroken custodial symmetry in the
Higgs system allowing to eliminate large contributions to the T parameter,
whereas the P_LR symmetry and the enlarged fermion representations provide a
custodial symmetry for flavour diagonal and flavour changing couplings of the
SM Z boson to left-handed down-type quarks. We diagonalise analytically the
mass matrices of charged and neutral gauge bosons including the first KK modes.
We present the mass matrices for quarks including heavy KK modes and discuss
the neutral and charged currents involving light and heavy fields. We give the
corresponding complete set of Feynman rules in the unitary gauge.Comment: 74 pages, 2 figures. clarifying comments and references added,
version to be published in JHE
Flavor from the Electroweak Scale
We discuss the possibility that flavor hierarchies arise from the electroweak
scale in a two Higgs doublet model, in which the two Higgs doublets jointly act
as the flavon. Quark masses and mixing angles are explained by effective Yukawa
couplings, generated by higher dimensional operators involving quarks and Higgs
doublets. Modified Higgs couplings yield important effects on the production
cross sections and decay rates of the light Standard Model like Higgs. In
addition, flavor changing neutral currents arise at tree-level and lead to
strong constraints from meson-antimeson mixing. Remarkably, flavor constraints
turn out to prefer a region in parameter space that is in excellent agreement
with the one preferred by recent Higgs precision measurements at the Large
Hadron Collider (LHC). Direct searches for extra scalars at the LHC lead to
further constraints. Precise predictions for the production and decay modes of
the additional Higgs bosons are derived, and we present benchmark scenarios for
searches at the LHC Run II. Flavor breaking at the electroweak scale as well as
strong coupling effects demand a UV completion at the scale of a few TeV,
possibly within the reach of the LHC.Comment: 58 pages, 22 figures, 12 table
Creating the fermion mass hierarchies with multiple Higgs bosons
After the Higgs boson discovery, it is established that the Higgs mechanism
explains electroweak symmetry breaking and generates the masses of all
particles in the Standard Model, with the possible exception of neutrino
masses. The hierarchies among fermion masses and mixing angles remain however
unexplained. We propose a new class of two Higgs doublet models in which a
flavor symmetry broken at the electroweak scale addresses this problem. The
models are strongly constrained by electroweak precision tests and the fact
that they produce modifications to Higgs couplings and flavor changing neutral
currents; they are also constrained by collider searches for extra scalar
bosons. The surviving models are very predictive, implying unavoidable new
physics signals at the CERN Large Hadron Collider, e.g. extra Higgs Bosons with
masses GeV.Comment: 5 pages, 2 figure