39 research outputs found
Stable matchings and linear programming
AbstractThis paper continues the work of Abeledo and Rothblum, who study nonbipartite stable matching problems from a polyhedral perspective. We establish here additional properties of fractional stable matchings and use linear programming to obtain an alternative polynomial algorithm for solving stable matching problems
BMSSM Implications for Cosmology
The addition of non-renormalizable terms involving the Higgs fields to the
MSSM (BMSSM) ameliorates the little hierarchy problem of the MSSM. We analyze
in detail the two main cosmological issues affected by the BMSSM: dark matter
and baryogenesis. The regions for which the relic abundance of the LSP is
consistent with WMAP and collider constraints are identified, showing that the
bulk region and other previously excluded regions are now permitted. Requiring
vacuum stability limits the allowed regions. Based on a two-loop finite
temperature effective potential analysis, we show that the electroweak phase
transition can be sufficiently first order in regions that for the MSSM are
incompatible with the LEP Higgs mass bound, including parameter values of
\tan\beta \lsim 5, m_{\tilde{t}_{1}} > m_t, m_Q << TeV.Comment: 28 pages, 4 figures. References adde
Neutrinoless double-beta decay with massive scalar emission
Searches for neutrino-less double-beta decay () place an
important constraint on models where light fields beyond the Standard Model
participate in the neutrino mass mechanism. While experimental
collaborations often consider various massless majoron models, including
various forms of majoron couplings and multi-majoron final-state processes,
none of these searches considered the scenario where the "majoron" is
not massless, ~MeV, of the same order as the -value of the
reaction. We consider this parameter region and estimate
constraints for of order MeV. The constraints are
affected not only by kinematical phase space suppression but also by a change
in the signal to background ratio characterizing the search. As a result,
constraints for diminish significantly below the
reaction threshold. This has phenomenological implications, which we illustrate
focusing on high-energy neutrino telescopes. Our results motivate a dedicated
analysis by collaborations, analogous to the dedicated analyses
targeting massless majoron models.Comment: 9 pages, 6 figures. v2: added App.A w/ phase space integrals, a few
added comments, match journal versio
Beyond MSSM Baryogenesis
Taking the MSSM as an effective low-energy theory, with a cut-off scale of a
few TeV, can make significant modifications to the predictions concerning the
Higgs and stop sectors. We investigate the consequences of such a scenario for
electroweak baryogenesis. We find that the window for MSSM baryogenesis is
extended and, most important, can be made significantly more natural.
Specifically, it is possible to have one stop lighter than the top and the
other significantly lighter than TeV simultaneously with the Higgs mass above
the LEP bound. In addition, various aspects concerning CP violation are
affected. Most notably, it is possible to have dynamical phases in the bubble
walls at tree level, providing CP violating sources for Standard Model
fermions.Comment: 20 pages, 2 figures; v2: added reference
Asymmetric Higgsino Dark Matter
In the supersymmetric framework, a higgsino asymmetry exists in the universe
before the electroweak phase transition. We investigate whether the higgsino is
a viable asymmetric dark matter candidate. We find that this is indeed
possible. The gauginos, squarks and sleptons must all be very heavy, such that
the only electroweak-scale superpartners are the higgsinos. The temperature of
the electroweak phase transition must be in the (1-10) GeV range.Comment: 5 pages, 2 figure
Scalar-mediated forward-backward asymmetry
A large forward-backward asymmetry in production, for large
invariant mass of the system, has been recently observed by the CDF
collaboration. Among the scalar mediated mechanisms that can explain such a
large asymmetry, only the t-channel exchange of a color-singlet weak-doublet
scalar is consistent with both differential and integrated cross
section measurements. Constraints from flavor changing processes dictate a very
specific structure for the Yukawa couplings of such a new scalar. No sizable
deviation in the differential or integrated production cross section
is expected at the LHC.Comment: 22 pages, 1 figure and 2 tables. v2: Corrected Eqs.(50,51,74),
adapted Fig.1, Tab.1 and relevant discussions. Extended discussion of top
decay and single to
Implications of large dimuon CP asymmetry in B_{d,s} decays on minimal flavor violation with low tan beta
The D0 collaboration has recently announced evidence for a dimuon CP
asymmetry in B_{d,s} decays of order one percent. If confirmed, this asymmetry
requires new physics. We argue that for minimally flavor violating (MFV) new
physics, and at low tan beta=v_u/v_d, there are only two four-quark operators
(Q_{2,3}) that can provide the required CP violating effect. The scale of such
new physics must lie below 260 GeV sqrt{tan beta}. The effect is universal in
the B_s and B_d systems, leading to S_{psi K}~sin(2beta)-0.15 and S_{psi
phi}~0.25. The effects on epsilon_K and on electric dipole moments are
negligible. The most plausible mechanism is tree-level scalar exchange. MFV
supersymmetry with low tan beta will be excluded. Finally, we explain how a
pattern of deviations from the Standard Model predictions for S_{psi phi},
S_{psi K} and epsilon_K can be used to test MFV and, if MFV holds, to probe its
structure in detail.Comment: 11 pages. v2: References adde
Implications of the CDF t\bar{t} Forward-Backward Asymmetry for Boosted Top Physics
New physics at a high scale Lambda can affect top-related observables at
O(1/Lambda^2) via the interference of effective four quark operators with the
SM amplitude. The (\bar{u} gamma_mu gamma^5 T^a u)(\bar{t} gamma^mu gamma^5 T^a
t) operator modifies the large M_{t\bar{t}} forward-backward asymmetry, and can
account for the recent CDF measurement. The (\bar{u} gamma_mu T^a u)(\bar{t}
gamma^mu T^a t) operator modifies the differential cross section, but cannot
enhance the cross section of ultra-massive boosted jets by more than 60%. The
hint for a larger enhancement from a recent CDF measurement may not persist
future experimental improvements, or may be a QCD effect that is not accounted
for by leading order and matched Monte Carlo tools or naive factorization. If
it comes from new physics, it may stem from new light states or an
O(1/Lambda^4) new physics effect.Comment: 7 pages, 2 figures and 2 tables. v2: References added. v3: Minor
clarifications and modifications; matches published versio