Search

We present a study of the b-ẵτ Yukawa unified supersymmetric SU(4)c x SU(2)L x SU(2)R model (with μ > 0), which predicts the existence of gluino--neutralino and stop--neutralino coannihilation scenarios compatible with the desired relic lightest supersymmetric particle neutralino dark matter abundance and other collider constraints. The next to lightest supersymmetric particle (NLSP) gluino or NLSP stop masses vary between 400 GeV and ~1 TeV. The NLSP gluinos will be accessible at the 14 TeV LHC, while we hope that the NSLP stop solutions will be probed in future LHC searches. We also identify regions of the parameter space in which the gluino and the lighter stop are closely degenerate in mass, interchangeably playing the role of NLSP and next to next to lightest supersymmetric particle (NNLSP). We also update a previous study of t-b-τ Yukawa unification and show that NLSP gluino of mass ~1 TeV, with a mass difference between the gluino and neutralino of less than 80 GeV, can be realized, consistent with the current collider and astrophysical constraints. We present benchmark points for b-τ and t-b-τ Yukawa unification that can be accessible at the LHC. [ABSTRACT FROM AUTHOR]

We show how in the standard electroweak model three SU(2)L Nambu monopoles, each carrying electromagnetic (EM) and Z magnetic fluxes, can merge (through Z strings) with a single U(1)Y Dirac monopole to yield a composite monopole that only carries EM magnetic flux. Compatibility with the Dirac quantization condition requires this composite monopole to carry six quanta (12π/e) of magnetic charge, independent of the electroweak mixing angle θw. The Dirac monopole is not regular at the origin and the energy of the composite monopole is therefore divergent. We discuss how this problem is cured by embedding U(1)Y in a grand unified group such as SU(5). A second composite configuration with only one Nambu monopole and a colored U(1)Y Dirac monopole that has minimal EM charge of 4π/e is also described. Finally, there exists a configuration with an EM charge of 8π/e as well as screened color magnetic charge. [ABSTRACT FROM AUTHOR]

The gauge symmetry SU(5)×U(1)χ is the unique maximal subgroup of SO(10) which retains manifest unification at MGUT of the Standard Model gauge couplings, especially if low scale supersymmetry is present. The spontaneous breaking of U(1)χ at some intermediate scale leaves unbroken a Z2 symmetry which is precisely "matter" parity. This yields a stable supersymmetric dark matter particle as well as topologically stable cosmic strings. Motivated by the weak gravity conjecture we impose unification of SU(5) and U(1)χ at an ultraviolet cutoff Λ∼α1/2ΛMP≈5×1017 GeV, where αΛ denotes the SU(5) gauge coupling at Λ and MP≈2.4×1018 GeV is the reduced Planck scale. The impact of dimension five operators suppressed by Λ on gauge coupling unification, proton lifetime estimates and b-τ Yukawa unification is discussed. In particular, the modified proton lifetime estimate for decay into e+π0 can be tested at Hyper-Kamiokande. We also discuss how the intermediate scale strings may survive inflation while the SU(5) monopoles are inflated away. The unbroken Z2 symmetry provides an intriguing link between dark matter, black holes carrying "quantum hair" and cosmic strings. [ABSTRACT FROM AUTHOR]

Motivated by the ongoing searches for new physics at the LHC, we explore the low energy consequences of a D-brane inspired SU(4)C×SU(2)L×SU(2)R (4-2-2) model. The Higgs sector consists of an SU(4) adjoint, a pair H+H¯ in (4,1,2)+(4¯,1,2), and a bidoublet field in h(1,2,2). With the SU(4) adjoint, the symmetry breaks to a left-right symmetric SU(3)C×U(1)B-L×SU(2)L×SU(2)R model. A missing partner mechanism protects the SU(2)R Higgs doublets in H, H¯, which subsequently break this latter symmetry at around to 104-106 GeV to the Standard Model. An inverse seesaw mechanism generates masses for the observed neutrinos and also yields a keV sterile neutrino that can play the role of dark matter if its mass lies in the keV range. Other phenomenological implications, including proton decay, are briefly discussed. [ABSTRACT FROM AUTHOR]

We consider a supersymmetric SU(4)c×SU(2)L×SU(2)R model with a minimal number of Higgs multiplets and Dirac and Majorana CP-violating phases in the neutrino flavor mixing matrix. The model incorporates the charged fermion masses and quark mixings, and uses type I seesaw to explain the solar and atmospheric neutrino oscillations. With the neutrino oscillation data of two mass squared differences and three flavor mixing angles, we employ thermal leptogenesis and the observed baryon asymmetry to find the allowed regions for the Dirac and Majorana phases. For a normal neutrino mass hierarchy, we find that the observed baryon asymmetry can be reproduced by a Dirac phase of around dCP=3p/2, which is strongly indicated by the recent T2K and NOνA data. For the case of inverted neutrino mass hierarchy, the predicted baryon asymmetry is not compatible with the observed value. [ABSTRACT FROM AUTHOR]

We revisit supersymmetric hybrid inflation in the context of the flipped SU(5) model. With minimal superpotential and minimal Kähler potential, and soft supersymmetry (SUSY) masses of order (1-100) TeV, compatibility with the Planck data yields a symmetry breaking scale M of flipped SU(5) close to (2-4)×1015 GeV. This disagrees with the lower limit M≳7×1015 GeV set from proton decay searches by the Super-Kamiokande collaboration. We show how M close to the unification scale 2×1016 GeV can be reconciled with SUSY hybrid inflation by employing a nonminimal Kähler potential. Proton decays into e+π0 with an estimated lifetime of order 1036 years. The tensor to scalar ratio r in this case can approach observable values ~10-4-10-3. [ABSTRACT FROM AUTHOR]

We implement inflation in a nonsupersymmetric SU(5) model based on a nonminimal coupling of the axion field to gravity. The isocurvature fluctuations are adequately suppressed, axions comprise the dark matter, proton lifetime estimates are of order 8×1034-3×1035 yr, and the observed baryon asymmetry arises via nonthermal leptogenesis. The presence of low-scale colored scalars ensures unification of the Standard Model gauge couplings and also helps in stabilizing the electroweak vacuum. [ABSTRACT FROM AUTHOR]

We explore the low-energy phenomenology of an F-theory-based SU(5) model which, in addition to the known quarks and leptons, contains Standard Model (SM) singlets and vectorlike color triplets and SU(2) doublets. Depending on their masses and couplings, some of these new particles may be observed at the LHC and future colliders. We discuss the restrictions by Cabibbo-Kobayashi-Maskawa matrix constraints on their mixing with the ordinary down quarks of the three chiral families. The model is consistent with gauge coupling unification at the usual supersymmetric GUT scale; dimension-five proton decay is adequately suppressed, while dimension-six decay mediated by the superheavy gauge bosons is enhanced by a factor of 5-7. The third generation charged fermion Yukawa couplings yield the corresponding low-energy masses in reasonable agreement with observations. The hierarchical nature of the masses of lighter generations is accounted for via nonrenormalizable interactions, with the perturbative vacuum expectation values (VEVs) of the SM singlet fields playing an essential role. [ABSTRACT FROM AUTHOR]

In μ-hybrid inflation a nonzero inflaton vacuum expectation value induced by supersymmetry breaking is proportional to the gravitino mass m3/2, which can be exploited to resolve the minimal supersymmetric standard model μ problem. We show how this scenario can be successfully implemented with m3/2~1-100 TeV and reheat temperature as low as 106 GeV by employing a minimal renormalizable superpotential coupled with a well-defined nonminimal Kähler potential. The tensor-to-scalar ratio r, a canonical measure of primordial gravity waves, in most cases is less than or of the order of 10-6-10-3. [ABSTRACT FROM AUTHOR]

A wide variety of unified models predict asymptotic relations at MGUT between the b quark and t lepton Yukawa couplings. Within the framework of supersymmetric SU(4)xSU(2)LxSU(2)R, we explore regions of the parameter space that are compatible with b - t quasi Yukawa Unification, Higgsinos being the lightest supersymmetric particles (≤1TeV) accompanied by a relatively low level of fine-tuning determined by the parameter ΔEW (~200). Among the colored sparticles, the stop weighs more than 1.5 TeV or so, whereas the squarks of the first two families are significantly heavier, approaching 10 TeV in some cases. The gluino mass is estimated to lie in the 2-4 TeV range which raises the important question: Will the LHC find the gluino? [ABSTRACT FROM AUTHOR]

We explore the implications of the t-b-τ (and b-τ) Yukawa coupling unification condition on the fundamental parameter space and sparticle spectroscopy in the minimal gauge mediated supersymmetry breaking model. We find that this scenario prefers values of the CP-odd Higgs mass mA ≳ 1 TeV, with all colored sparticle masses above 3 TeV. These predictions will be hard to test at LHC13 but they may be testable at the high-energy LHC (HE-LHC) 33 TeV or a 100 TeV collider. Both the t-b-τ and the b-τ Yukawa coupling unification prefer a relatively light gravitino with mass ≲30 eV, which makes it a candidate hot dark matter particle. However, it cannot account for more than 15% of the observed dark matter density. [ABSTRACT FROM AUTHOR]

We study a grand unified theories inspired supersymmetric model with nonuniversal gaugino masses that can explain the observed muon g -- 2 anomaly while simultaneously accommodating an enhancement or suppression in the h → γγ decay channel. In order to accommodate these observations and mh ≃ 125 to 126 GeV, the model requires a spectrum consisting of relatively light sleptons whereas the colored sparticles are heavy. The predicted stau mass range corresponding to Rγγ ≥ 1.1 is 100 GeV≲ mτ... ≲ 200 GeV. The constraint on the slepton masses, particularly on the smuons, arising from considerations of muon g -- 2 is somewhat milder. The slepton masses in this case are predicted to lie in the few hundred GeV range. The colored sparticles turn out to be considerably heavier with mḡ ≳ 4.5 TeV and mt1... ≳ 3.5 TeV, which makes it challenging for these to be observed at the 14 TeV LHC. [ABSTRACT FROM AUTHOR]

We propose that inflation and dark matter have a common origin, connected to the neutrino mass generation scheme. As a model we consider spontaneous breaking of global lepton number within the seesaw mechanism. We show that it provides an acceptable inflationary scenario consistent with the recent cosmic microwave background B-mode observation by the BICEP2 experiment. The scheme may also account for the baryon asymmetry of the Universe through leptogenesis for reasonable parameter choices. [ABSTRACT FROM AUTHOR]

We consider two classes of supersymmetric models with nonuniversal gaugino masses at the grand unification scale MGm in an attempt to resolve the apparent muon g - 2 anomaly encountered in the Standard Model. We explore two distinct scenarios, one in which all gaugino masses have the same sign at MGUT, and a second case with opposite sign gaugino masses. The sfermion masses in both cases are assumed to be universal at MGUT. We exploit the nonuniversality among gaugino masses to realize large mass splitting between the colored and noncolored sfermions. Thus, the sleptons can have masses in the few hundred GeV range, whereas the colored sparticles turn out to be an order of magnitude or so heavier. In both models the resolution of the muon g - 2 anomaly is compatible, among other things, with a 125-126 GeV Higgs boson mass and the WMAP dark matter bounds. [ABSTRACT FROM AUTHOR]

We propose a pseudo-Goldstone boson dark matter (pGDM) particle in SO(10) grand unified theory (GUT). Due to its Goldstone nature, this pGDM evades the direct DM detection experiments which, otherwise, severely constrain the parameter space of DM models. In SO(10), the pGDM is embedded as a linear combination of the Standard Model (SM) singlet scalars in 16H and ̅126H representations. We consider two scenarios for the intermediate route of SO(10) symmetry breaking (SB) to the SM: SU(5)×U(1)X and Pati-Salam the SU(4)c×SU(2)L×SU(2)R(4-2-2) gauge groups. The vacuum expectation value of ̅126H, which triggers the breaking of U(1)X and 4-2-2 symmetry in the two scenarios, respectively, determines the pGDM lifetime whose astrophysical lower bound provides one of the most stringent constraints. For the 4-2-2 route to SO(10), the successful SM gauge coupling unification requires the 4-2-2 breaking scale to be O(1011) GeV, and most of the parameter space is excluded. For the SU(5)×U(1)X route, on the other hand, the U(1)X breaking scale can be significantly higher, and a wide range of the parameter space is allowed. Furthermore, the proton lifetime in the SU(5) case is predicted to be 4.53×1034 years, which lies well within the sensitivity reach of the Hyper-Kamiokande experiment. We also examine the constraints on the model parameter space from the Large Hadron Collider and the indirect DM search by Fermi-LAT and MAGIC experiments. [ABSTRACT FROM AUTHOR]

We investigate the impact of Coleman-Weinberg inflation on the stochastic gravity wave background spectrum emitted by intermediate-scale cosmic strings. The string network is partially inflated and reenters the horizon at later times after the end of inflation, such that the short string loops are not produced. This leads to a significant modification of the gravity wave spectrum that we explore in detail. We find that Coleman-Weinberg inflation can help to satisfy the Parkes Pulsar Timing Array (PPTA) bound for dimensionless string tension values in the range Gμ1.1×10-10. We also identify the modified gravity wave spectra which, in the case of inflation, are compatible with the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) data. We then discuss the formation of monopoles and strings at the same breaking scale and the compatibility of the Monopole, Astrophysics and Cosmic Ray Observatory (MACRO) bound with the PPTA bound, and also with the NANOGrav data. Finally, an example of a realistic nonsupersymmetric E6 model incorporating successful Coleman-Weinberg inflation is presented in which monopoles and strings both survive inflation and are present at an observable level. [ABSTRACT FROM AUTHOR]

We propose a SU(5)×U(1)X×U(1)PQ model, where U(1)X is the generalization of the B-L (baryon minus lepton number) gauge symmetry and U(1)PQ is the global Peccei-Quinn (PQ) symmetry. There are four fermions families in ¯5+10 representations of SU(5), a mirror family in 5+10 representations, and three SU(5) singlet Majorana fermions. The U(1)X related anomalies all cancel in the presence of the Majorana neutrinos. The SU(5) symmetry is broken at MGUT≃(6-9)×1015 GeV and the proton lifetime τp is estimated to be well within the expected sensitivity of the future hyper-Kamiokande experiment, τp≲1.3×1035 years. The SU(5) breaking also triggers the breaking of the PQ symmetry, resulting in axion dark matter (DM), with the axion decay constant fa of order MGUT or somewhat larger. The CASPEr experiment can search for such an axion DM candidate. The Hubble parameter during inflation must be low, Hinf≲109 GeV, in order to successfully resolve the axion domain wall, axion DM isocurvature and SU(5) monopole problems. With the identification of the U(1)X breaking Higgs field with the inflaton field, we implement inflection-point inflation, which is capable of realizing the desired value for Hinf. The vectorlike fermions in the model are essential for achieving successful unification of the SM gauge couplings as well as the phenomenological viability of both axion DM and inflation scenario. [ABSTRACT FROM AUTHOR]

Gauging the global B-L (Baryon number minus Lepton number) symmetry in the standard model (SM) is well motivated since anomaly cancellations require the introduction of three right-handed neutrinos which play an essential role in naturally generating tiny SM neutrino masses through the seesaw mechanism. In the context of the B-L extended SM, we propose a pseudo-Goldstone boson dark matter (DM) scenario in which the imaginary component of a complex B-L Higgs field serves as the DM in the universe. The DM relic density is determined by the SM Higgs boson mediated process, but its elastic scattering with nucleons through the exchange of Higgs bosons is highly suppressed due to its pseudo-Goldstone boson nature. The model is therefore free from the constraints arising from direct DM detection experiments. We identify regions of the model parameter space for reproducing the observed DM density compatible with the constraints from the Large Hadron Collider and the indirect DM searches by Fermi Large Area Telescope and Major Atmospheric Gamma Imaging Cherenkov. [ABSTRACT FROM AUTHOR]

We investigate supersymmetric hybrid inflation in a realistic model based on the gauge symmetry SU(4)c×SU(2)L×SU(2)R. The minimal supersymmetric standard model (MSSM) μ term arises, following Dvali, Lazarides, and Shafi, from the coupling of the MSSM electroweak doublets to a gauge singlet superfield, which plays an essential role in inflation. The primordial monopoles are inflated away by arranging that the SU(4)c×SU(2)L×SU(2)R symmetry is broken along the inflationary trajectory. The interplay between the (above) μ coupling, the gravitino mass, and the reheating following inflation is discussed in detail. We explore regions of the parameter space that yield gravitino dark matter and observable gravity waves with the tensor-to-scalar ratio r∼10-4-10-3. [ABSTRACT FROM AUTHOR]

The standard model (SM) supplemented by type II seesaw and a SM gauge-singlet scalar dark matter (DM) is a very simple framework to incorporate the observed neutrino oscillations and provide a plausible DM candidate. In this framework, the scalar DM naturally has a leptophilic nature with a pair annihilating mainly into the SM SU(2)L triplet Higgs scalar of type II Seesaw which, in turn, decay into leptons. In this work, we consider indirect signatures of this leptophilic DM and examine the spectrum of the cosmic ray electron/positron flux from DM pair annihilations in the Galactic halo. Given an astrophysical background spectrum of the cosmic ray electron/positron flux, we find that the contributions from DM annihilations can nicely fit the observed data from the AMS-02, DAMPE and Fermi-LAT collaborations, with a multi-TeV range of DM mass and a boost factor for the DM annihilation cross section of O(1000). The boost factor has a tension with the Fermi-LAT data for gamma-ray from dwarf spheroidal galaxies and the limit from CMB anisotropies, which can be ameliorated with enhanced local DM density by a factor of about two. [ABSTRACT FROM AUTHOR]

We present a class of models in the framework of gauge mediation supersymmetry breaking where the messenger fields transform in the adjoint representation of the standard model gauge symmetry. To avoid unacceptably light right-handed sleptons in the spectrum we introduce a nonzero U(1)B-L D-term. This leads to an additional contribution to the soft supersymmetry breaking mass terms which makes the right-handed slepton masses compatible with the current experimental bounds. We show that in this framework the observed 125 GeV Higgs boson mass can be accommodated with the sleptons accessible at the LHC, while the squarks and gluinos lie in the multi-TeV range. We also discuss the issue of the fine-tuning and show that the desired relic dark matter abundance can also be accommodated. [ABSTRACT FROM AUTHOR]

We study the neutralinos and sleptons in multilepton final states at the LHC in light of (g - 2)μanomaly. We scan the minimal supersymmetric standard model parameters relevant to (g - 2)μ(and focus on three distinct cases with different neutralino compositions. The explanation of (g - 2)μ excess at 2σ range requires the smuon (μl) to be lighter than ~500(1000) GeV for tan ß = 10(50). Correspondingly the two lightest neutralinos, X10, X20 have to be lighter than -300(650) GeV and 900 (1500) GeV, respectively. We explore the prospects of searching these light neutralinos and smuons at the LHC. The upcoming run of the LHC will be able to set 95% CL exclusion limit on M-X20 (~650 - 1300 GeV) and mj (~670 - 775 GeV) with M-X10 -- 100 - 250 GeV at 3000 fb-1 integrated luminosity in multilepton + ET channel. [ABSTRACT FROM AUTHOR]

We present a class of supersymmetric models in which symmetry considerations alone dictate the form of the soft SUSY breaking Lagrangian. We develop a class of minimal models, denoted as sMSSM--for flavor symmetry-based minimal supersymmetric standard model--that respect a grand unified symmetry such as SO(10) and a non-Abelian flavor symmetry H which suppresses SUSY-induced flavor violation. Explicit examples are constructed with the flavor symmetry being gauged SU(2)H and SO(3)H with the three families transforming as 2+1 and 3 representations, respectively. A simple solution is found in the case of SU(2)H for suppressing the flavor violating D-terms based on an exchange symmetry. Explicit models based on SO(3)H without the D-term problem are developed. In addition, models based on discrete non-Abelian flavor groups are presented which are automatically free from D-term issues. The permutation group S3 with a 2 + 1 family assignment, as well as the tetrahedral group A4 with a 3 assignment are studied. In all cases, a simple solution to the SUSY CP problem is found, based on spontaneous CP violation leading to a complex quark mixing matrix. We develop the phenomenology of the resulting sMSSM, which is controlled by seven soft SUSY breaking parameters for both the 2 + 1 assignment and the 3 assignment of fermion families. These models are special cases of the phenomenological MSSM (pMSSM), but with symmetry restrictions. We discuss the parameter space of sMSSM compatible with LHC searches, B-physics constraints and dark matter relic abundance. Fine-tuning in these models is relatively mild, since all SUSY particles can have masses below about 3 TeV. [ABSTRACT FROM AUTHOR]