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Yingchuan Li

Publications and source records attributed to Yingchuan Li.

17 recordsLinked to original sources
arXiv2011

Identifying Sneutrino Dark Matter: Interplay between the LHC and Direct Search

Under R-parity, the lightest supersymmetric particle (LSP) is stable and may serve as a good dark matter candidate. The R-parity can be naturally introduced with a gauge origin at TeV scale. We go over why a TeV scale B-L gauge extension of the minimal supersymmetric standard model (MSSM) is one of the most natural, if not demanded, low energy supersymmetric models. In the presence of a TeV scale Abelian gauge symmetry, the (predominantly) right-handed sneutrino LSP can be a good dark matter candidate. Its identification at the LHC is challenging because it does not carry any standard model charge. We show how we can use the correlation between the LHC experiments (dilepton resonance signals) and the direct dark matter search experiments (such as CDMS and XENON) to identify the right-handed sneutrino LSP dark matter in the B-L extended MSSM.

hep-ph↗
arXiv2010

A Comprehensive Analysis of Electric Dipole Moment Constraints on CP-violating Phases in the MSSM

We analyze the constraints placed on individual, flavor diagonal CP-violating phases in the minimal supersymmetric extension of the Standard Model (MSSM) by current experimental bounds on the electric dipole moments (EDMs) of the neutron, Thallium, and Mercury atoms. We identify the four CP-violating phases that are individually highly constrained by current EDM bounds, and we explore how these phases and correlations among them are constrained by current EDM limits. We also analyze the prospective implications of the next generation of EDM experiments. We point out that all other CP-violating phases in the MSSM are not nearly as tightly constrained by limits on the size of EDMs. We emphasize that a rich set of phenomenological consequences is potentially associated with these generically large EDM-allowed phases, ranging from B physics, electroweak baryogenesis, and signals of CP-violation at the CERN Large Hadron Collider and at future linear colliders. Our numerical study takes into account the complete set of contributions from one- and two-loop EDMs of the electron and quarks, one- and two-loop Chromo-EDMs of quarks, the Weinberg 3-gluon operator, and dominant 4-fermion CP-odd operator contributions, including contributions which are both included and not included yet in the CPsuperH2.0 package. We also introduce an open-source numerical package, 2LEDM, which provides the complete set of two-loop electroweak diagrams contributing to the electric dipole moments of leptons and quarks.

hep-ph↗
arXiv2010

LHC Signals for Coset Electroweak Gauge Bosons in Warped/Composite PGB Higgs Models

The framework of a warped extra dimension with the Standard Model (SM) fields propagating in it is a very well-motivated extension of the SM since it can address both the Planck-weak and flavor hierarchy problems of the SM. Within this framework, solution to the little hierarchy problem motivates extending the SM electroweak (EW) 5D gauge symmetry in such a way that its breakdown to the SM delivers the SM Higgs boson. We study signals at the large hadron collider (LHC) for the extra EW (called coset) gauge bosons, a fundamental ingredient of this framework. The coset gauge bosons, due to their unique EW gauge quantum numbers [doublets of SU(2)_L], do not couple at leading order to two SM particles. We find that, using the associated production of the charged coset gauge bosons via their coupling to SM bottom quark and a (light) KK top quark, the LHC can have a 3σreach of \sim 2 (2.6) TeV for the coset gauge boson masses with \sim 100 (1000) fb^{-1} luminosity. Since current theoretical framework(s) suggest an {\em indirect} lower limit on coset gauge boson masses of >3 TeV, luminosity or energy upgrade of LHC is likely to be crucial in observing these states.

hep-ph↗
arXiv2010

Testing CP Violation in ZZH Interactions at the LHC

We study genuine CP-odd observables at the LHC to test the CP property of the ZZH interaction for a Higgs boson with mass below the threshold to a pair of gauge bosons via the process p,p -> Z,H -> l+,l-,b,bbar. We illustrate the analysis by including a CP-odd ZZH coupling, and show how to extract the CP asymmetries in the signal events. After selective kinematical cuts to suppress the SM backgrounds plus an optimal Log-likelihood analysis, we find that, with a CP violating coupling btilde = 0.25, a CP asymmetry may be established at a 3 sigma (5 sigma) level with an integrated luminosity of about 30 (50) fb^-1 at the LHC.

hep-ph↗
arXiv2010

Vacuum Stability, Perturbativity, and Scalar Singlet Dark Matter

We analyze the one-loop vacuum stability and perturbativity bounds on a singlet extension of the Standard Model (SM) scalar sector containing a scalar dark matter candidate. We show that the presence of the singlet-doublet quartic interaction relaxes the vacuum stability lower bound on the SM Higgs mass as a function of the cutoff and lowers the corresponding upper bound based on perturbativity considerations. We also find that vacuum stability requirements may place a lower bound on the singlet dark matter mass for given singlet quartic self coupling, leading to restrictions on the parameter space consistent with the observed relic density. We argue that discovery of a light singlet scalar dark matter particle could provide indirect information on the singlet quartic self-coupling.

hep-ph↗
arXiv2010

MSSM Baryogenesis and Electric Dipole Moments: An Update on the Phenomenology

We explore the implications of electroweak baryogenesis for future searches for permanent electric dipole moments in the context of the minimal supersymmetric extension of the Standard Model (MSSM). From a cosmological standpoint, we point out that regions of parameter space that over-produce relic lightest supersymmetric particles can be salvaged only by assuming a dilution of the particle relic density that makes it compatible with the dark matter density: this dilution must occur after dark matter freeze-out, which ordinarily takes place after electroweak baryogenesis, implying the same degree of dilution for the generated baryon number density as well. We expand on previous studies on the viable MSSM regions for baryogenesis, exploring for the first time an orthogonal slice of the relevant parameter space, namely the (tanβ, m_A) plane, and the case of non-universal relative gaugino-higgsino CP violating phases. The main result of our study is that in all cases lower limits on the size of the electric dipole moments exist, and are typically on the same order, or above, the expected sensitivity of the next generation of experimental searches, implying that MSSM electroweak baryogenesis will be soon conclusively tested.

hep-ph↗
arXiv2009

Genuine CP-odd Observables at the LHC

We discuss how to construct genuine CP-odd observables at the LHC. We classify the observables according to the even and odd properties under the naive T-transformation (\hat{T}). There are two classes of observables of our interests: CP-odd and \hat{T}-even; CP-odd and \hat{T}-odd. We expect them to have broad applications to many processes in theories beyond Standard Model with CP violation. For the purpose of illustration, we use simple example of W+W- production and subsequent decays at the LHC, where the CP violation effects are parameterized by effective CP-violating operators of WWZ coupling. We find significant sensitivity to the CP-odd couplings.

hep-ph↗
arXiv2008

Bino-driven Electroweak Baryogenesis with highly suppressed Electric Dipole Moments

It is conventional wisdom that successful electroweak baryogenesis in the Minimal Supersymmetric extension of the Standard Model (MSSM) is in tension with the non-observation of electric dipole moments (EDMs), since the level of CP-violation responsible for electroweak baryogenesis is believed to generate unavoidably large EDMs. We show that CP-violation in the bino-Higgsino sector of the MSSM can account for successful electroweak baryogenesis without inducing large EDMs. This observation weakens the correlation between electroweak baryogenesis and EDMs, and makes the bino-driven electroweak baryogenesis scenario the least constrained by EDM limits. Taking this observation together with the requirement of a strongly first-order electroweak phase transition, we argue that a bino-driven scenario with a light stop is the most phenomenologically viable MSSM electroweak baryogenesis scenario.

hep-ph↗
arXiv2008

Higgs-Higgsino-Gaugino Induced Two Loop Electric Dipole Moments

We compute the complete set of Higgs-mediated chargino-neutralino two-loop contributions to the electric dipole moments (EDMs) of the electron and neutron in the minimal supersymmetric standard model (MSSM). We study the dependence of these contributions on the parameters that govern CP-violation in the MSSM gauge-gaugino-Higgs-Higgsino sector. We find that contributions mediated by the exchange of W H^\pm and Z A^0 pairs, where H^\pm and A^0 are the charged and CP-odd Higgs scalars, respectively, are comparable to or dominate over those mediated by the exchange of neutral gauge bosons and CP-even Higgs scalars. We also emphasize that the result of this complete set of diagrams is essential for the full quantitative study of a number of phenomenological issues, such as electric dipole moment searches and their implications for electroweak baryogenesis.

hep-ph↗
arXiv2007

Atmospheric Neutrino Mixing and b-s Transitions: Testing Lopsided SO(10) Flavor Structure in B physics

We point out that the correlation between the large atmospheric neutrino mixing and the $b \to s$ transition, if exists, comes from the lopsided flavor structure in SO(10) grand unification theory. We suggest testing the correlation by studying the deviation of $S_{ϕK_S}$ and $S_{η' K_S}$ from the standard model predictions along with the constraints from $ΔM_{B_S}$ and $b\to s γ$ in a realistic SO(10) model with lopsided flavor structure. We find a specific correlation between $S_{ϕK_S}$ and $S_{η' K_S}$ that is intrinsic to the lopsided structure and discuss how to confirm or rule out this flavor pattern by the more accurate measurements of these CP violation quantities in B decay.

hep-ph↗
arXiv2006

Leptogenesis in Realistic SO(10) Models

We study the origin of baryonic matter via leptogenesis in realistic SO(10) models, in particular, in a new lopsided mass matrix model introduced recently by three of the authors. By introducing simple CP-violating phases in the mass matrix of the right-handed neutrinos, the model generates sufficient baryon asymmetry without fine-tuning. We compare this result with other realistic SO(10) models.

hep-ph↗
arXiv2006

Fixing Two-Nucleon Weak-Axial Coupling L_{1,A} From mu-d Capture

We calculate the muon capture rate on the deuteron to next-to-next-to-leading order in the pionless effective field theory. The result can be used to constrain the two-nucleon isovector axial coupling L_{1,A} to +/- 2 fm^3 if the muon capture rate is measured to 2% level. From this, one can determine the neutrino-deuteron break up reactions and the pp-fusion cross section in the sun to a same level of accuracy.

nucl-th↗
arXiv2005

An SO(10) GUT Model With Lopsided Mass Matrix and Neutrino Mixing Angle theta_13

An alternative supersymmetric SO(10) grand unification model with lopsided fermion mass matrices is introduced. It generates a large solar-neutrino-mixing angle through the neutrinos' Dirac mass matrix constrained by the SO(10) group structure, avoiding the fine-tuning required in the Majorana mass matrix of right-handed neutrinos. The model fits well the known data on masses and mixings of quarks and leptons, and predicts a sizable lepton mixing $\sin^22θ_{13}\simeq 0.074$, which is significantly larger than that of the original lopsided model.

hep-ph↗
arXiv2004

Deuteron Compton Scattering in Effective Field Theory: Spin-Dependent Cross Sections and Asymmetries

Polarized Compton scattering on the deuteron is studied in nuclear effective field theory. A set of tensor structures is introduced to define 12 independent Compton amplitudes. The scalar and vector amplitudes are calculated up to ${\cal O}((Q/Λ)^2)$ in low-energy power counting. Significant contribution to the vector amplitudes is found to come from the spin-orbit type of relativistic corrections. A double-helicity dependent cross section $Δ_1 σ= (σ_{+1-1}-σ_{+1+1})/2$ is calculated to the same order, and the effect of the nucleon isoscalar spin-dependent polarizabilities is found to be smaller than the effect of isoscalar spin-independent ones. Contributions of spin-independent polarizabilities are investigated in various asymmetries, one of which has as large as 12 (26) percent effect at the center-of-mass photon energy 30 (50) MeV.

nucl-th↗
arXiv2004

Deuteron Compton Scattering in Effective Field Theory And Spin-Independent Nucleon Polarizabilities

Deuteron Compton scattering is calculated to $\mathcal{O}(Q^2)$ in pionless effective field theory using a dibaryon approach. The vector amplitude, which was not included in the previous pionless calculations, contributes to the cross section at $\mathcal{O}(Q^2)$ and influences significantly the extracted values of nucleon electric polarizability at incident photon energy 49 MeV. We recommend future high precision deuteron compton scattering experiments being performed at 25-35 MeV photon energy where the nucleon polarizability effects are appreciable and the pionless effective field theory is most reliable. For example, a measurement at 30 MeV with a 3% error will constrain the isoscalar nucleon electric polarizability $% α_{0}$ with a $\sim 30%$ error.

nucl-th↗
arXiv2004

Drell-Hearn-Gerasimov Sum-Rule for the Deuteron in Nuclear Effective Field Theory

The Drell-Hearn-Gerasimov sum rule for the deuteron is studied in nuclear effective field theory. The low-energy theorem for the spin-dependent Compton amplitude $f_1(ω)$ is derived to the next-to-leading order in low-energy expansion. The spin-dependent photodisintegration cross section $σ^P-σ^A$ is calculated to the same order, and its contribution to the dispersive integral is evaluated.

nucl-th↗