L. Everett - Wisconsin University, Madison

L. Everett
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L. Everett
Wisconsin University, Madison
United States

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High Energy Physics - Phenomenology (49)
High Energy Physics - Theory (11)
High Energy Physics - Experiment (8)
Astrophysics (5)
Cosmology and Nongalactic Astrophysics (1)
Physics - Instrumentation and Detectors (1)
Nuclear Experiment (1)
High Energy Astrophysical Phenomena (1)

Publications Authored By L. Everett

We study the effects of considering nontrivial unphysical lepton sector phases on the group theoretical properties of the flavor and generalized CP symmetry elements in the case where there are three light, distinct Majorana neutrino species. This approach highlights the similarities and differences between generalized CP symmetries in the charged lepton and neutrino sectors while further elucidating the group properties of the generalized CP symmetry elements. Read More

We explore the model-building and phenomenology of flavored gauge mediation models of supersymmetry breaking in which the electroweak Higgs doublets and the SU(2) messenger doublets are connected by a discrete non-Abelian symmetry. The embedding of the Higgs and messenger fields into representations of this non-Abelian Higgs-messenger symmetry results in specific relations between the Standard Model Yukawa couplings and the messenger-matter Yukawa interactions. Taking the concrete example of an S(3) Higgs-messenger symmetry, we demonstrate that while the minimal implementation of this scenario suffers from a severe mu/B_mu problem that is well-known from ordinary gauge mediation, expanding the Higgs-messenger field content allows for the possibility that mu and B_mu can be separately tuned, allowing for the possibility of phenomenologically viable models of the soft supersymmetry breaking terms. Read More

We investigate the question of electroweak naturalness within the deflected mirage mediation (DMM) framework for supersymmetry breaking in the minimal supersymmetric standard model (MSSM). The class of DMM models considered are nine-parameter theories that fall within the general classification of the 19-parameter phenomenological MSSM (pMSSM). Our results show that these DMM models have regions of parameter space with very low electroweak fine-tuning, at levels comparable to the pMSSM. Read More

We complete the study of a class of string-motivated effective supergravity theories in which modulus-induced soft supersymmetry breaking is sufficiently suppressed in the observable sector so as to be competitive with anomaly-mediated supersymmetry breaking. Here we consider deflected mirage mediation (DMM), where contributions from gauge mediation are added to those arising from gravity mediation and anomaly mediation. We update previous work that surveyed the rich parameter space of such theories, in light of data from the CERN Large Hadron Collider (LHC) and recent dark matter detection experiments. Read More

Authors: C. Adams, J. R. Alonso, A. M. Ankowski, J. A. Asaadi, J. Ashenfelter, S. N. Axani, K. Babu, C. Backhouse, H. R. Band, P. S. Barbeau, N. Barros, A. Bernstein, M. Betancourt, M. Bishai, E. Blucher, J. Bouffard, N. Bowden, S. Brice, C. Bryan, L. Camilleri, J. Cao, J. Carlson, R. E. Carr, A. Chatterjee, M. Chen, S. Chen, M. Chiu, E. D. Church, J. I. Collar, G. Collin, J. M. Conrad, M. R. Convery, R. L. Cooper, D. Cowen, H. Davoudiasl, A. De Gouvea, D. J. Dean, G. Deichert, F. Descamps, T. DeYoung, M. V. Diwan, Z. Djurcic, M. J. Dolinski, J. Dolph, B. Donnelly, D. A. Dwyer, S. Dytman, Y. Efremenko, L. L. Everett, A. Fava, E. Figueroa-Feliciano, B. Fleming, A. Friedland, B. K. Fujikawa, T. K. Gaisser, M. Galeazzi, D. C. Galehouse, A. Galindo-Uribarri, G. T. Garvey, S. Gautam, K. E. Gilje, M. Gonzalez-Garcia, M. C. Goodman, H. Gordon, E. Gramellini, M. P. Green, A. Guglielmi, R. W. Hackenburg, A. Hackenburg, F. Halzen, K. Han, S. Hans, D. Harris, K. M. Heeger, M. Herman, R. Hill, A. Holin, P. Huber, D. E. Jaffe, R. A. Johnson, J. Joshi, G. Karagiorgi, L. J. Kaufman, B. Kayser, S. H. Kettell, B. J. Kirby, J. R. Klein, Yu. G. Kolomensky, R. M. Kriske, C. E. Lane, T. J. Langford, A. Lankford, K. Lau, J. G. Learned, J. Ling, J. M. Link, D. Lissauer, L. Littenberg, B. R. Littlejohn, S. Lockwitz, M. Lokajicek, W. C. Louis, K. Luk, J. Lykken, W. J. Marciano, J. Maricic, D. M. Markoff, D. A. Martinez Caicedo, C. Mauger, K. Mavrokoridis, E. McCluskey, D. McKeen, R. McKeown, G. Mills, I. Mocioiu, B. Monreal, M. R. Mooney, J. G. Morfin, P. Mumm, J. Napolitano, R. Neilson, J. K. Nelson, M. Nessi, D. Norcini, F. Nova, D. R. Nygren, G. D. Orebi Gann, O. Palamara, Z. Parsa, R. Patterson, P. Paul, A. Pocar, X. Qian, J. L. Raaf, R. Rameika, G. Ranucci, H. Ray, D. Reyna, G. C. Rich, P. Rodrigues, E. Romero Romero, R. Rosero, S. D. Rountree, B. Rybolt, M. C. Sanchez, G. Santucci, D. Schmitz, K. Scholberg, D. Seckel, M. Shaevitz, R. Shrock, M. B. Smy, M. Soderberg, A. Sonzogni, A. B. Sousa, J. Spitz, J. M. St. John, J. Stewart, J. B. Strait, G. Sullivan, R. Svoboda, A. M. Szelc, R. Tayloe, M. A. Thomson, M. Toups, A. Vacheret, M. Vagins, R. G. Van de Water, R. B. Vogelaar, M. Weber, W. Weng, M. Wetstein, C. White, B. R. White, L. Whitehead, D. W. Whittington, M. J. Wilking, R. J. Wilson, P. Wilson, D. Winklehner, D. R. Winn, E. Worcester, L. Yang, M. Yeh, Z. W. Yokley, J. Yoo, B. Yu, J. Yu, C. Zhang

The US neutrino community gathered at the Workshop on the Intermediate Neutrino Program (WINP) at Brookhaven National Laboratory February 4-6, 2015 to explore opportunities in neutrino physics over the next five to ten years. Scientists from particle, astroparticle and nuclear physics participated in the workshop. The workshop examined promising opportunities for neutrino physics in the intermediate term, including possible new small to mid-scale experiments, US contributions to large experiments, upgrades to existing experiments, R&D plans and theory. Read More

We perform a model-independent analysis of the possible residual Klein and generalized CP symmetries associated with arbitrary lepton mixing angles in the case that there are three light Majorana neutrino species. This approach emphasizes the unique role of the Majorana phases and provides a useful framework in which to discuss the origin of the Dirac CP phase in scenarios with spontaneously broken flavor and generalized CP symmetries. The method is shown to reproduce known examples in the literature based on tribimaximal and bitrimaximal mixing patterns, and is used to investigate these issues for the case of a particular (GR1) golden ratio mixing pattern. Read More

After the extraordinary discovery of the Higgs boson at the LHC, the next goal is to pin down its underlying dynamics by measuring the Higgs self-couplings, along with its couplings to gauge and matter particles. As a prototype model of new physics in the scalar sector, we consider the Two Higgs Doublet Model (2HDM) with CP-conservation, and evaluate the prospects for measuring the trilinear scalar couplings among the CP-even Higgs bosons $h$ and $H$ ($\lambda^{hhh}$, $\lambda^{hhH}$, $\lambda^{hHH}$) at LHC14. The continuum and resonant production of CP-even Higgs boson pairs, $hh$ and $hH$, offer complementary probes of the scalar potential away from the light-Higgs decoupling limit. Read More

We advocate a search for an extended scalar sector at the LHC via $hh$ production, where $h$ is the 125 GeV Higgs boson. A resonance feature in the $hh$ invariant mass is a smoking gun of an $s$-channel heavy Higgs resonance, $H$. With one $h$ decaying to two photons and the other decaying to $b$-quarks, the resonant signal may be discoverable above the $hh$ continuum background for $M_H<$ 1 TeV. Read More

We simulate the measurement of the triscalar Higgs coupling at LHC(8,14) via pair production of h(125 GeV). We find that the most promising hh final state is bb gamma gamma. We account for deviations of the triscalar coupling from its SM value and study the effects of this coupling on the hh cross-section and distributions with cut-based and multivariate methods. Read More


This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $CP$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

Affiliations: 1IZTECH, 2U of Wisconsin, 3Concordia, 4Ankara U, IZTECH, 5Concordia

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. Read More

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 $\Delta B =1, 2$ 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. Read More

We present a correlated analysis for the $\Delta B =1, 2$ processes which occur via $b\to s$ transitions within models with a family non-universal $U(1)^\prime$. We take a model-independent approach, and only require family universal charges for the first and second generations and small fermion mixing angles. The results of our analysis show that within this class of models, the anomalies in $B_s - \bar B_s$ mixing and the time-dependent CP asymmetries of the penguin-dominated $B_d \to (\pi, \phi, \eta', \rho, \omega, f_0)K_S$ decays can be accommodated. Read More

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. Read More

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. Read More

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. Read More

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. Read More

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. Read More

Kination dominated quintessence models of dark energy have the intriguing feature that the relic abundance of thermal cold dark matter can be significantly enhanced compared to the predictions from standard cosmology. Previous treatments of such models do not include a realistic embedding of inflationary initial conditions. We remedy this situation by constructing a viable inflationary model in which the inflaton and quintessence field are the same scalar degree of freedom. Read More

Within the broad context of quark-lepton unification, we investigate the implications of broken continuous family symmetries which result from requiring that in the limit of exact symmetry, the Dirac mass matrices yield hierarchical masses for the quarks and charged leptons, but lead to degenerate light neutrino masses as a consequence of the seesaw mechanism, without requiring hierarchical right-handed neutrino mass terms. Quark mixing is then naturally small and proportional to the size of the perturbation, but lepton mixing is large as a result of degenerate perturbation theory, shifted from maximal mixing by the size of the perturbation. Within this approach, we study an illustrative two-family prototype model with an SO(2) family symmetry, and discuss extensions to three-family models. Read More

We consider the possibility that the quark condensate formed by QCD confinement generates Majorana neutrino masses m_\nu via dimension seven operators. No degrees of freedom beyond the Standard Model are necessary, below the electroweak scale. Obtaining experimentally acceptable neutrino masses requires the new physics scale \Lambda ~ TeV, providing a new motivation for weak-scale discoveries at the LHC. Read More

We explore the hypothesis that the Cabibbo angle is an expansion parameter for lepton as well as quark mixing. Cabibbo effects are deviations from zero mixing for the quarks but are deviations from unknown mixings for the leptons, such that lepton mixing is veiled by a Cabibbo haze. We present a systematic classification of parametrizations and catalog the leading order Cabibbo effects. Read More

Quark-lepton unification suggests Cabibbo-sized effects in lepton mixings, which we call Cabibbo haze. We give simple examples and explore possible Wolfenstein-like parametrizations of the MNSP matrix which incorporate leptonic Cabibbo shifts. We find that the size of the CHOOZ angle is not always correlated with the observability of CP violation. Read More

After an introduction recalling the theoretical motivation for low energy (100 GeV to TeV scale) supersymmetry, this review describes the theory and experimental implications of the soft supersymmetry-breaking Lagrangian of the general minimal supersymmetric standard model (MSSM). Extensions to include neutrino masses and nonminimal theories are also discussed. Topics covered include models of supersymmetry breaking, phenomenological constraints from electroweak symmetry breaking, flavor/CP violation, collider searches, and cosmological constraints including dark matter and implications for baryogenesis and inflation. Read More

The supersymmetric CP problem is studied within superstring-motivated extensions of the MSSM with an additional U(1)' gauge symmetry broken at the TeV scale. This class of models offers an attractive solution to the mu problem of the MSSM, in which U(1)' gauge invariance forbids the bare mu term, but an effective mu parameter is generated by the vacuum expectation value of a Standard Model singlet S which has superpotential coupling of the form SH_uH_d to the electroweak Higgs doublets. The effective mu parameter is thus dynamically determined as a function of the soft supersymmetry breaking parameters, and can be complex if the soft parameters have nontrivial CP-violating phases. Read More

At present we know nothing about the nature of the dark energy accounting for about 70% of the energy density of the Universe. One possibility is that the dark energy is provided by an extremely light field, the quintessence, rolling down its potential. Even though the underlying particle theory responsible for the present quintessential behaviour of our Universe is unknown, such a theory is likely to have contact with supersymmetry, supergravity or (super)string theory. Read More

Affiliations: 1CERN, 2MCTP and, 3Southampton U, 4CERN, 5MCTP and

We explore supersymmetric Type I string-motivated three-family scenarios in which the Standard Model is embedded within two sets of intersecting D branes with U(1)-extended Pati-Salam gauge groups. We study a model inspired by the Shiu-Tye Type IIB orientifold, in which a three-family scenario is obtained by assuming that the gauge symmetry breaking takes place in two stages; the Pati-Salam group arises from diagonal breaking of the U(N) gauge groups, which is then broken to the SM gauge group. We investigate the diagonal breaking scenario in detail and find that generically there are difficulties involved in decoupling the exotic Higgs remnants. Read More

Affiliations: 1MCTP and University of Michigan, 2MCTP and University of Michigan, 3MCTP and University of Michigan, 4MCTP and University of Michigan, 5MCTP and University of Michigan

The gluino contributions to the $C'_{7,8}$ Wilson coefficients for $b->s \gamma$ are calculated within the unconstrained MSSM. New stringent bounds on the $\delta^{RL}_{23}$ and $\delta^{RR}_{23}$ mass insertion parameters are obtained in the limit in which the SM and SUSY contributions to $C_{7,8}$ approximately cancel. Such a cancellation can plausibly appear within several classes of SUSY breaking models in which the trilinear couplings exhibit a factorized structure proportional to the Yukawa matrices. Read More

We study the implications of interpreting the recent muon g-2 deviation from the Standard Model prediction as evidence for virtual superpartners, with very general calculations that include effects of phases and are consistent with all relevant constraints. The most important result is that there are upper limits on masses: at least one superpartner mass is below about 350 GeV (for the theoretically preferred value of tan(beta)=35) and may be produced at the Fermilab Tevatron in the upcoming run, and there must be chargino, neutralino, and slepton masses below about 600 GeV. In addition, tan(beta) must be larger than about 8. Read More

The phenomenological possibilities of the Randall-Sundrum non-compact extra dimension scenario with the AdS horizon increased to approximately a millimeter length, corresponding to an effective brane tension of TeV^4, are investigated. The corrections to the Newtonian potential are found to be the only observationally accessible probe of this scenario, as previously suggested in the literature. In particular, the presence of the continuum of KK modes does not lead to any observable collider signatures. Read More

There are many low-energy models of supersymmetry breaking parameters which are motivated by theoretical and experimental considerations. Here, we discuss some of the lesser-known theories of low-energy supersymmetry, and outline their phenomenological consequences. In some cases, these theories have more gauge symmetry or particle content than the Minimal Supersymmetric Standard Model. Read More

We examine the flavor structure of the trilinear superpotential couplings which can result from embedding the Standard Model within D brane sectors in Type IIB orientifold models, which are examples within the Type I string framework. We find in general that the allowed flavor structures of the Yukawa coupling matrices to leading order are given by basic variations on the "democratic" texture ansatz. In certain interesting cases, the Yukawa couplings have a novel structure in which a single right-handed fermion couples democratically at leading order to three left-handed fermions. Read More

Affiliations: 1Michigan U., 2Penn U., 3Penn U., 4Fermilab

We describe the features of supersymmetric spectra, alternative to and qualitatively different from that of most versions of the MSSM. The spectra are motivated by extensions of the MSSM with an extra U(1)' gauge symmetry, expected in many grand unified and superstring models, which provide a plausible solution to the mu problem, both for models with supergravity and for gauge-mediated supersymmetry breaking. Typically, many or all of the squarks are rather heavy (larger than one TeV), especially for the first two families, as are the sleptons in the supergravity models. Read More

Recently it has been demonstrated that large phases in softly broken supersymmetric theories are consistent with electric dipole moment constraints, and are motivated in some (Type I) string models. Here we consider whether large flavor-independent soft phases may be the dominant (or only) source of all CP violation. In this framework $\epsilon$ and $\epsilon'/\epsilon$ can be accommodated, and the SUSY contribution to the B system mixing can be large and dominant. Read More

We investigate the possibility of large CP- violating phases in the soft breaking terms derived in superstring models. The bounds on the electric dipole moments (EDM's) of the electron and neutron are satisfied through cancellations occuring because of the structure of the string models. Three general classes of four-dimensional string models are considered: (i) orbifold compactifications of perturbative heterotic string theory, (ii) scenarios based on Ho\v{r}ava-Witten theory, and (iii) Type I string models (Type IIB orientifolds). Read More

We examine the soft supersymmetry breaking parameters that result from various ways of embedding the Standard Model (SM) on D-branes within the Type I string picture, allowing the gaugino masses and $\mu$ to have large CP- violating phases. One embedding naturally provides the relations among soft parameters to satisfy the electron and neutron electric dipole moment constraints even with large phases, while with other embeddings large phases are not allowed. The string models provide some motivation for large phases in the soft breaking parameters. Read More

We study the blowing-up of the four-dimensional Z_3 orientifold of Angelantonj, Bianchi, Pradisi, Sagnotti and Stanev (ABPSS) by giving nonzero vacuum expectation values (VEV's) to the twisted sector moduli blowing-up modes. The blowing-up procedure induces a Fayet-Iliopoulos (FI) term for the ``anomalous'' U(1), whose magnitude depends linearly on the VEV's of the blowing-up modes. To preserve the N=1 supersymmetry, non-Abelian matter fields are forced to acquire nonzero VEV's, thus breaking (some of) the non-Abelian gauge structure and decoupling some of the matter fields. Read More

We investigate the low energy physics implications of a prototype quasi-realistic superstring model with an anomalous U(1). First, we present the techniques utilized to compute the mass spectrum and superpotential couplings at the string scale, and demonstrate the results for the effective theory along a particular flat direction/"restabilized vacuum" of the model. We then analyze the gauge symmetry breaking patterns and renormalization group equations to determine the mass spectrum at the electroweak scale for a particular numerical example with a realistic Z-Z' hierarchy. Read More

We continue the investigation of the physics implications of a class of flat directions for a prototype quasi-realistic free fermionic string model (CHL5), building upon the results of the previous paper in which the complete mass spectrum and effective trilinear couplings of the observable sector were calculated to all orders in the superpotential. We introduce soft supersymmetry breaking mass parameters into the model, and investigate the gauge symmetry breaking patterns and the renormalization group analysis for two representative flat directions, which leave an additional $U(1)'$ as well as the SM gauge group unbroken at the string scale. We study symmetry breaking patterns that lead to a phenomenologically acceptable $Z-Z'$ hierarchy, $M_{Z^{'}} \sim {\cal O}(1~{\rm TeV})$ and $ 10^{12}~{\rm GeV}$ for electroweak and intermediate scale $U(1)^{'}$ symmetry breaking, respectively, and the associated mass spectra after electroweak symmetry breaking. Read More