arXiv subjects

Lisa L. Everett

Publications and source records attributed to Lisa L. Everett.

At least 37 records · Page 2Linked to original sources

arXiv2013

Scrutinizing h(125) in Two Higgs Doublet Models at the LHC, ILC, and Muon Collider

The discovery at the LHC of a scalar particle with properties that are so far consistent with the SM Higgs boson is one of the most important advances in the history of particle physics. The challenge of future collider experiments is to determine whether its couplings will show deviations from the SM Higgs, as this would indicate new physics at the TeV scale, and also to probe the flavor structure of the Yukawa couplings. As a benchmark alternative to the SM Higgs, we consider a generic two Higgs doublet model (2HDM) and analyze the precision to which the LHC14, an ILC250, 500, 1000 GeV and a 125 GeV Muon Collider (MC) can determine the gauge and Yukawa couplings. We allow for correlations among the couplings. We include the impact of a Higgs total width measurement, indirectly at the LHC and ILC and by a direct scan at the MC. We also discuss pattern relations among the couplings that can test for singlet or doublet Higgs extensions of 2HDMs.

hep-ph↗

arXiv2013

Discriminators of 2 Higgs Doublets at the LHC14, ILC and MuonCollider(125): A Snowmasss White Paper

The historic LHC discovery of the 125 GeV particle with properties that closely resemble the Standard Model (SM) Higgs boson verifies our understanding of electroweak symmetry breaking, but solidifies the need for a resolution to the hierarchy problem. Many extensions of the SM that address the hierarchy problem contain a non-minimal Higgs sector. Therefore, as a benchmark alternative to the SM Higgs mechanism, we study a general 2 Higgs doublet model (2HDM-G) framework for evaluating future sensitivity to Higgs couplings. We study how well it can be distinguished from the SM Higgs boson by future measurements at LHC14, ILC (250, 500,1000 GeV) and a Muon Collider (125 GeV). Additionally, our study bears on singlet Higgs extensions of two Higgs doublet models through predicted coupling relationships.

hep-ph↗

arXiv2012

2HDM Portal Dark Matter: LHC data and the Fermi-LAT 135 GeV Line

We study a two Higgs doublet model augmented by a scalar dark matter particle that provides an excellent fit to the LHC Higgs data and the Fermi-LAT 135 GeV line. The heavy CP-even Higgs boson, which predominantly mediates annihilation and scattering, must have a coupling to weak gauge bosons at or below percent level to suppress the continuum gamma-ray spectrum below the limit from the Fermi-LAT data and the anti-proton spectrum constrained by the PAMELA data. Discovering or excluding this CP-even Higgs boson at the LHC with a mass between 265 and 280 GeV and an enhanced diphoton branching ratio is crucial to test this scenario.

hep-ph↗

arXiv2012

The 2HDM-X and Large Hadron Collider Data

We study the consistency of two Higgs doublet models in light of the new bosonic particle discovery at the LHC. We work within a general setup that we call the 2HDM-X, in which the quarks couple to both scalar doublets with aligned couplings such that flavor-changing neutral currents are absent at tree level. The 2HDM-X encompasses the traditional Type I, Type II, lepton specific, and flipped models, but also provides for more general possibilities. The best fit to the current data with a suppressed tau tau signal and a b bbar signal of Standard Model strength is given by the 2HDM-X with specific parameter choices; however, very good fits are also obtained within the lepton-specific model and a democratic model, the 2HDM-D, in which both the up-type and down-type quarks couple to each doublet with equal strengths. The approach provides a general framework in which to interpret future LHC Higgs data within extensions of the Standard Model with two Higgs doublets.

hep-ph↗

arXiv2012

Golden Ratio Neutrino Mixing and $A_5$ Flavor Symmetry

We provide a systematic and thorough exploration of lepton flavor models in which the solar mixing angle is related to the golden ratio. For scenarios in which the solar mixing angle is given by the inverse cotangent of the golden ratio, we demonstrate that $A_5$ is the smallest non-Abelian finite group that contains all of the symmetries necessary to enforce this specific lepton mixing pattern. Within this context, we propose two lepton flavor models that yield this mixing pattern through the breaking of $A_5$ at leading order to the Klein four subgroup in the neutrino sector. Both models have triplet embeddings of the lepton doublets as well as the charged lepton singlets. In the charged lepton sector, the residual symmetry is $Z_5$ in the first model, while in the second model, $A_5$ is broken completely at leading order. For the second model, the reactor mixing angle vanishes at leading order and is of the order of the square of the Cabibbo angle at next-to-leading order, which is allowed by the global analysis of current lepton data.

hep-ph↗

arXiv2011

Landscape of Supersymmetric Particle Mass Hierarchies in Deflected Mirage Mediation

With the aim of uncovering viable regions of parameter space in deflected mirage mediation (DMM) models of supersymmetry breaking, we study the landscape of particle mass hierarchies for the lightest four non-Standard Model states for DMM models and compare the results to that of minimal supergravity/constrained MSSM (mSUGRA/CMSSM) models, building on previous studies of Feldman, Liu, and Nath. Deflected mirage mediation is a string-motivated scenario in which the soft terms include comparable contributions from gravity mediation, gauge mediation, and anomaly mediation. DMM allows a wide variety of phenomenologically preferred models with light charginos and neutralinos, including novel patterns in which the heavy Higgs particles are lighter than the lightest superpartner. We use this analysis to motivate two DMM benchmark points to be used for more detailed collider studies. One model point has a higgsino-dominated lightest superpartner and a compressed yet heavy spectrum, while the other has a stau NLSP and similar features to mSUGRA/CMSSM models, but with a slightly less stretched spectrum.

hep-ph↗

arXiv2011

Gravitational Fermion Production in Inflationary Cosmology

We revisit the gravitational production of massive Dirac fermions in inflationary cosmology with a focus on clarifying the analytic computation of the particle number density in both the large and the small mass regimes. For the case in which the masses of the gravitationally produced fermions are small compared to the Hubble expansion rate at the end of inflation, we obtain a universal result for the number density that is nearly independent of the details of the inflationary model. The result is identical to the case of conformally coupled scalars up to an overall multiplicative factor of order unity for reasons other than just counting the fermionic degrees of freedom.

astro-ph.CO↗

arXiv2011

The Double Cover of the Icosahedral Symmetry Group and Quark Mass Textures

We investigate the idea that the double cover of the rotational icosahedral symmetry group is the family symmetry group in the quark sector. The icosahedral (A5) group was previously proposed as a viable family symmetry group for the leptons. To incorporate the quarks, it is highly advantageous to extend the group to its double cover, as in the case of tetrahedral (A4) symmetry. We provide the basic group theoretical tools for flavor model-building based on the binary icosahedral group I' and construct a model of the quark masses and mixings that yields many of the successful predictions of the well-known U(2) quark texture models.

hep-ph↗

arXiv2010

Sneutrino Dark Matter: Symmetry Protection and Cosmic Ray Anomalies

We present an R-parity conserving model of sneutrino dark matter within a Higgs-philic U(1)' extension of the minimal supersymmetric standard model. In this theory, the mu parameter and light Dirac neutrino masses are generated naturally upon the breaking of the U(1)' gauge symmetry. The leptonic and hadronic decays of sneutrinos in this model, taken to be the lightest and next-to-lightest superpartners, allow for a natural fit to the recent results reported by the PAMELA experiment.

hep-ph↗

arXiv2010

Phenomenological Implications of Deflected Mirage Mediation: Comparison with Mirage Mediation

We compare the collider phenomenology of mirage mediation and deflected mirage mediation, which are two recently proposed "mixed" supersymmetry breaking scenarios motivated from string compactifications. The scenarios differ in that deflected mirage mediation includes contributions from gauge mediation in addition to the contributions from gravity mediation and anomaly mediation also present in mirage mediation. The threshold effects from gauge mediation can drastically alter the low energy spectrum from that of pure mirage mediation models, resulting in some cases in a squeezed gaugino spectrum and a gluino that is much lighter than other colored superpartners. We provide several benchmark deflected mirage mediation models and construct model lines as a function of the gauge mediation contributions, and discuss their discovery potential at the LHC.

hep-ph↗

arXiv2009

Phenomenological Implications of Supersymmetric Family Non-universal U(1)-prime Models

We construct a class of anomaly-free supersymmetric U(1)' models that are characterized by family non-universal U(1)' charges motivated from E_6 embeddings. The family non-universality arises from an interchange of the standard roles of the two SU(5) 5* representations within the 27 of E_6 for the third generation. We analyze U(1)' and electroweak symmetry breaking and present the particle mass spectrum. The models, which include additional Higgs multiplets and exotic quarks at the TeV scale, result in specific patterns of flavor-changing neutral currents in the b to s transitions that can accommodate the presently observed deviations inthis sector from the SM predictions.

hep-ph↗

arXiv2009

The Right Side of Tev Scale Spontaneous R-Parity Violation

We study a simple extension of the minimal supersymmetric Standard Model in which the Abelian sector of the theory consists of B-L and right-handed isospin. In the minimal model this Abelian gauge structure is broken to the standard model hypercharge gauge group by non-vanishing vacuum expectation values of the right-handed sneutrinos, resulting in spontaneous R-parity violation. This theory can emerge as a low energy effective theory of a left-right symmetric theory realized at a high scale. We determine the mass spectrum of the theory, and discuss the generation of neutrino masses and R-parity violating interactions. The possibility of distinguishing between R-parity violating models with a gauged B-L broken at the TeV scale at the Large Hadron Collider is discussed.

hep-ph↗

arXiv2009

$b \to s$ Transitions in Family-dependent $U(1)^\prime$ Models

We analyze flavor-changing-neutral-current (FCNC) effects in the $b\to s$ transitions that are induced by family non-universal $U(1)'$ gauge symmetries. After systematically developing the necessary formalism, we present a correlated analysis for the $ΔB =1, 2$ processes. We adopt a model-independent approach in which we only require family-universal charges for the first and second generations and small fermion mixing angles. We analyze the constraints on the resulting parameter space from $B_s - \bar B_s$ mixing and the time-dependent CP asymmetries of the penguin-dominated $B_d \to (π, ϕ, η', ρ, ω, f_0)K_S$ decays. Our results indicate that the currently observed discrepancies in some of these modes with respect to the Standard Model predictions can be consistently accommodated within this general class of models.

hep-ph↗

arXiv2009

Icosahedral (A5) Family Symmetry and the Golden Ratio Prediction for Solar Neutrino Mixing

We investigate the possibility of using icosahedral symmetry as a family symmetry group in the lepton sector. The rotational icosahedral group, which is isomorphic to A5, the alternating group of five elements, provides a natural context in which to explore (among other possibilities) the intriguing hypothesis that the solar neutrino mixing angle is governed by the golden ratio. We present a basic toolbox for model-building using icosahedral symmetry, including explicit representation matrices and tensor product rules. As a simple application, we construct a minimal model at tree level in which the solar angle is related to the golden ratio, the atmospheric angle is maximal, and the reactor angle vanishes to leading order. The approach provides a rich setting in which to investigate the flavor puzzle of the Standard Model.

hep-ph↗

arXiv2008

Deflected Mirage Mediation: A Framework for Generalized Supersymmetry Breaking

We present a general phenomenological framework for dialing between gravity mediation, gauge mediation, and anomaly mediation. The approach is motivated from recent developments in moduli stabilization, which suggest that gravity mediated terms can be effectively loop suppressed and thus comparable to gauge and anomaly mediated terms. The gauginos exhibit a mirage unification behavior at a "deflected" scale, and gluinos are often the lightest colored sparticles. The approach provides a rich setting in which to explore generalized supersymmetry breaking at the LHC.

hep-ph↗

arXiv2008

Moduli Stabilization and Supersymmetry Breaking in Deflected Mirage Mediation

We present a model of supersymmetry breaking in which the contributions from gravity/modulus, anomaly, and gauge mediation are all comparable. We term this scenario "deflected mirage mediation," which is a generalization of the KKLT-motivated mirage mediation scenario to include gauge mediated contributions. These contributions deflect the gaugino mass unification scale and alter the pattern of soft parameters at low energies. In some cases, this results in a gluino LSP and light stops; in other regions of parameter space, the LSP can be a well-tempered neutralino. We demonstrate explicitly that competitive gauge-mediated terms can naturally appear within phenomenological models based on the KKLT setup by addressing the stabilization of the gauge singlet field which is responsible for the masses of the messenger fields. For viable stabilization mechanisms, the relation between the gauge and anomaly contributions is identical in most cases to that of deflected anomaly mediation, despite the presence of the Kahler modulus. Turning to TeV scale phenomenology, we analyze the renormalization group evolution of the supersymmetry breaking terms and the resulting low energy mass spectra. The approach sets the stage for studies of such mixed scenarios of supersymmetry breaking at the LHC.

hep-ph↗

arXiv2007

Dirac Neutrino Masses from Generalized Supersymmetry Breaking

We demonstrate that Dirac neutrino masses in the experimentally preferred range are generated within supersymmetric gauge extensions of the Standard Model with a generalized supersymmetry breaking sector. If the usual superpotential Yukawa couplings are forbidden by the additional gauge symmetry (such as a U(1)'), effective Dirac mass terms involving the "wrong Higgs" field can arise either at tree level due to hard supersymmetry breaking fermion Yukawa couplings, or at one-loop due to nonanalytic or "nonholomorphic" soft supersymmetry breaking trilinear scalar couplings. As both of these operators are naturally suppressed in generic models of supersymmetry breaking, the resulting neutrino masses are naturally in the sub-eV range. The neutrino magnetic and electric dipole moments resulting from the radiative mechanism also vanish at one-loop order.

hep-ph↗

arXiv2007

Connecting LHC, ILC, and Quintessence

If the cold dark matter consists of weakly interacting massive particles (WIMPs), anticipated measurements of the WIMP properties at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) will provide an unprecedented experimental probe of cosmology at temperatures of order 1 GeV. It is worth emphasizing that the expected outcome of these tests may or may not be consistent with the picture of standard cosmology. For example, in kination-dominated quintessence models of dark energy, the dark matter relic abundance can be significantly enhanced compared to that obtained from freeze out in a radiation-dominated universe. Collider measurements then will simultaneously probe both dark matter and dark energy. In this article, we investigate the precision to which the LHC and ILC can determine the dark matter and dark energy parameters under those circumstances. We use an illustrative set of four benchmark points in minimal supergravity in analogy with the four LCC benchmark points. The precision achievable together at the LHC and ILC is sufficient to discover kination-dominated quintessence, under the assumption that the WIMPs are the only dark matter component. The LHC and ILC can thus play important roles as alternative probes of both dark matter and dark energy.

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