254 research outputs found
Nuclei as Laboratories: Nuclear Tests of Fundamental Symmetries
The prospect of a rare isosotope accelerator facility opens up possibilities
for a new generation of nuclear tests of fundamental symmetries. In this talk,
I survey the current landscape of such tests and discuss future opportunities
that a new facility might present.Comment: To appear in proceedings of 3rd ANL/MSU/INT/JINA Theory Workshop,
Argonne National Laboratory (April, 2006); 13 page
Chiral Symmetries and Low Energy Searches for New Physics
I discuss low energy searches for new physics beyond the Standard Model,
identifying the role played by chiral symmetries in these searches and in
various new physics scenarios. I focus in particular on electric dipole moment
searches; precision studies of weak decays and electron scattering; and
neutrino properties and interactions.Comment: Talk given at 5th International Workshop on Chiral Dynamics,
Durham/Chapel Hill, NC (September, 2006); 12 page
Electric Dipole Moments: A Global Analysis
We perform a global analysis of searches for the permanent electric dipole
moments (EDMs) of the neutron, neutral atoms, and molecules in terms of six
leptonic, semileptonic, and nonleptonic interactions involving photons,
electrons, pions, and nucleons. Translating the results into fundamental
CP-violating effective interactions through dimension six involving Standard
Model particles, we obtain rough lower bounds on the scale of beyond the
Standard Model CP-violating interactions ranging from 1.5 TeV for the electron
EDM to 1300 TeV for the nuclear spin-independent electron-quark interaction. We
show that future measurements involving systems or combinations of systems with
complementary sensitivities to the low-energy parameters may extend the mass
reach by an order of magnitude or more.Comment: 15 pages, 1 figur
Top Down Electroweak Dipole Operators
We derive present constraints on, and prospective sensitivity to, the
electric dipole moment (EDM) of the top quark () implied by searches for
the EDMs of the electron and nucleons. Above the electroweak scale , the
arises from two gauge invariant operators generated at a scale that also mix with the light fermion EDMs under renormalization group
evolution at two-loop order. Bounds on the EDMs of first generation fermion
systems thus imply bounds on . Working in the leading log-squared
approximation, we find that the present upper bound on is roughly
cm for TeV, except in regions of finely tuned
cancellations that allow for to be up to fifty times larger. Future
and probes may yield an order of magnitude increase in
sensitivity, while inclusion of a prospective proton EDM search may lead to an
additional increase in reach.Comment: 7 pages, 6 figure
Electron-to-Tau Lepton Flavor Violation at the Electron-Ion Collider
We analyze the potential sensitivity of a search for
conversion at a proposed electron-ion collider (EIC) facility. To that end, we
calculate the cross sections for events in a leptoquark
framework assuming that the leptoquark masses are on the order of several
hundred GeV or more. Given present limits on leptoquarks from direct searches
at HERA and rare decay processes, an EIC sensitive to 0.1 fb
cross sections could probe previously unexplored regions of parameter space for
these lepton flavor violating events (assuming 90 GeV center-of-mass energy and
10 fb integrated luminosity). Depending on the species of leptoquark and
flavor structure of the couplings, an EIC search could surpass the HERA and
rare process sensitivity to conversion amplitudes by as much
as an order of magnitude or more. We also derive updated limits on quark
flavor-diagonal LFV leptoquark interactions using the most recent BaBar
search. We find that limits from an EIC
search could be competitive with the most recent
limit for a subset of the quark flavor-diagonal
leptoquark couplings. Using an SU(5) GUT model in which leptoquark couplings
are constrained by the neutrino masses and mixing, we illustrate how observable
leptoquark-induced conversion can be consistent with
stringent LFV limits imposed by and
conversion searches.Comment: 19 pages, 7 figure
Electroweak Baryogenesis, Electric Dipole Moments, and Higgs Diphoton Decays
We study the viability of electroweak baryogenesis in a two Higgs doublet
model scenario augmented by vector-like, electroweakly interacting fermions.
Considering a limited, but illustrative region of the model parameter space, we
obtain the observed cosmic baryon asymmetry while satisfying present
constraints from the non-observation of the permanent electric dipole moment
(EDM) of the electron and the combined ATLAS and CMS result for the Higgs boson
diphoton decay rate. The observation of a non-zero electron EDM in a next
generation experiment and/or the observation of an excess (over the Standard
Model) of Higgs to diphoton events with the 14 TeV LHC run or a future
collider would be consistent with generation of the observed baryon asymmetry
in this scenario.Comment: 22 pages, 3 figure
Probing the Higgs portal at the LHC through resonant di-Higgs production
We investigate resonant di-Higgs production as a means of probing extended scalar sectors that include a 125 GeV Standard Model-like Higgs boson. For concreteness, we consider a gauge singlet Higgs portal scenario leading to two mixed doublet-singlet states, h_1,2. For m_h_2 > 2 m_h_1, the resonant di-Higgs production process p p -> h_2 -> h_1 h_1 will lead to final states associated with the decaying pair of Standard Model-like Higgs scalars. We focus on h_2 production via gluon fusion and on the b b tau^+ tau^- final state. We find that discovery of the h_2 at the LHC may be achieved with ~ 100 fb^-1 of integrated luminosity for benchmark parameter choices relevant to cosmology. Our analysis directly maps onto the decoupling limits of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and more generically onto extensions of the Standard Model Higgs sector in which a heavy scalar produced through gluon fusion decays to a pair of Standard Model-like Higgs bosons
Cuts, Cancellations and the Closed Time Path: The Soft Leptogenesis Example
By including all leading quantum-statistical effects at finite temperature,
we show that no net asymmetry of leptons and sleptons is generated from soft
leptogenesis, save the possible contribution from the resonant mixing of
sneutrinos. This result contrasts with different conclusions appearing in the
literature that are based on an incomplete inclusion of quantum statistics. We
discuss vertex and wave-function diagrams as well as all different possible
kinematic cuts that nominally lead to CP-violating asymmetries. The present
example of soft leptogenesis may therefore serve as a paradigm in order to
identify more generally applicable caveats relevant to alternative scenarios
for baryogenesis and leptogenesis, and it may provide useful guidance in
constructing viable models.Comment: 38 page
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