arXiv subjects

Tianjun Li

Publications and source records attributed to Tianjun Li.

At least 235 records · Page 13Linked to original sources

arXiv2012

A Heavy SM-like Higgs and a Light Stop from Yukawa-Deflected Gauge Mediation

To obtain a SM-like Higgs boson around 125 GeV in the Minimal Supersymmetric Standard Model with minimal gauge mediation of supersymmetry breaking (GMSB), a heavy stop at multi-TeV level is needed and incurs severe fine-tuning, which can be ameliorated in the framework of the deformed GMSB with visible-hidden direct Yukawa interactions (YGMSB). We examine some general features of the YGMSB and focus on the scenario with Higgs-messenger couplings (H-YGMSB) which can automatically maintain the minimal flavor violation (MFV). It turns out that such a Yukawa mediation scenario can give a large -A_t and -m_{stop_L,R}^2, leading to a maximal stop mixing, and thus can readily give a light stop (stop_1) below the TeV scale. However, we find that in the minimal H-YGMSB scenario, m_{H_u}^2 is too large and then the electroweak symmetry breaking is inconsistent with the large stop mixing. To solve this problem, we modify the hidden sectors in two ways, adding a new strong gauge dynamics or introducing the (10,10_bar) messengers. For each case we present some numerical study.

hep-ph↗

arXiv2012

Primordial Synthesis: F-SU(5) SUSY Multijets, 145-150 GeV LSP, Proton & Rare Decays, 125 GeV Higgs Boson, and WMAP7

We examine the first ATLAS Collaboration 8 TeV 5.8/fb supersymmetry (SUSY) multijet data observations in the context of No-Scale Flipped SU(5) with extra TeV-Scale vector-like flippon multiplets, dubbed F-SU(5), finding that the recent 8 TeV collider data is statistically consistent with our prior 7 TeV results. Furthermore, we synthesize all currently ongoing experiments searching for beyond the Standard Model (BSM) physics with this fit to the 8 TeV data, establishing a suggestive global coherence within a No-Scale F-SU(5) high-energy framework. The SUSY mass scale consistent with all BSM data consists of the region of the F-SU(5) model space within 660 ~< M_{1/2} ~< 760 GeV, which corresponds to sparticle masses of 133 ~< M(chi_1^0) ~< 160 GeV, 725 ~< M(t_1) ~< 845 GeV, and 890 ~< M(g) ~< 1025 GeV. We suggest that the tight non-trivial correspondence between the SUSY multijets, direct and indirect searches for dark matter, proton decay, rare-decay processes, the observed Higgs boson mass, and the measured dark matter relic density, is strongly indicative of a deeper fundamental relationship. We additionally suggest a simple mechanism for enhancing the capture efficiency of F-SU(5) SUSY multijets, which results in a 93% suppression in ATLAS reported background events, but only a 27% decrease in Monte Carlo simulated F-SU(5) multijet events.

hep-ph↗

arXiv2012

Constraints on the Universal Varying Yukawa Couplings: from SM-like to Fermiophobic

Varying the Standard Model (SM) fermion Yukawa couplings universally by a generic positive scale factor ($F_{Yu}$), we study the phenomenological fit to the current available experimental results for the Higgs boson search at hadron colliders. We point out that the Higgs production cross section and its decay branching ratio to $γγ$ can be varied oppositely by $F_{Yu}$ to make their product almost invariant. Thus, our scenario and the SM Higgs are indistinguishable in the inclusive $H\to γγ$ channel. The current measurements on direct Yukawa coupling strength in the $H\to b\bar{b}/ττ$ channel are not precise enough to fix the scale factor $F_{Yu}$. The most promising is the vector-boson-fusion channel in which the CMS has already observed possible suppression effect on the Yukawa couplings. Further more, the global $χ^2$ fit of the experimental data can get the optimal value by introducing a suppression factor $F_{Yu}\sim1/2$ on the SM Yukawa couplings.

hep-ph↗

arXiv2012

Correlating LHCb B_s^0 to μ^+ μ^- Results with the ATLAS-CMS Multijet Supersymmetry Search

We show that the No-Scale Flipped SU(5) construction is transparently consistent with recent LHCb results for B_s^0 to μ^+ μ^- decays, due primarily to suppression from the rather small value of tanβ~ 20 that is globally enforced across the model space. This fact should be interpreted in conjunction with the demonstrated evasion of mass limits from the ATLAS and CMS SUSY searches and the more important potential explanation of small observed excesses in the multijet data. The No-Scale Flipped SU(5) benchmark model that best fits these excesses has a gaugino mass scale of M_{1/2} = 708 GeV, which drives masses for the bino-dominated LSP m_χ_1^0 = 143.4 GeV, light stop m_t1 = 786 GeV, gluino m_g = 952 GeV, and heavy squark m_uL = 1490 GeV. The corresponding total prediction for the rare B-decay of Br(B_s^0 to μ^+ μ^-) = 3.5 x 10^-9 suggests that the SUSY contribution may indeed be much smaller than that expected from the Standard Model in this framework, fitting quite comfortably within the very tightly constrained region remaining viable after the most recent LHCb measurements.

hep-ph↗

arXiv2012

Testing No-Scale F-SU(5): A 125 GeV Higgs Boson and SUSY at the 8 TeV LHC

We celebrate the recent Higgs discovery announcement with our experimental colleagues at the LHC and look forward to the implications that this success will bring to bear upon the continuing search for supersymmetry (SUSY). The model framework named No-Scale F-SU(5) possesses the rather unique capacity to provide a light CP-even Higgs boson mass in the favored 124-126 GeV window while simultaneously retaining a testably light SUSY spectrum that is consistent with emerging low-statistics excesses beyond the Standard Model expectation in the ATLAS and CMS multijet data. In this letter we review the distinctive F-SU(5) mechanism that forges the physical 125 GeV Higgs boson and make a specific assessment of the ATLAS multijet SUSY search observables that may be expected for a 15/fb delivery of 8 TeV data in this model context. Based on our Monte Carlo study, we anticipate that the enticing hints of a SUSY signal observed in the 7 TeV data could be amplified in the 8 TeV results. Moreover, if the existing signal is indeed legitimate, we project that the rendered gains in significance will be sufficient to conclusively rule out an alternative attribution to statistical fluctuation at that juncture.

hep-ph↗

arXiv2012

Supersymmetric Dark Matter at XENON100 and the LHC: No-Scale F-SU(5) Stringy Correlations

We complete an investigation of the observable signatures of No-Scale flipped SU(5) x U(1)_X grand unified theory with TeV-scale vector-like particles (No-Scale F-SU(5)) at the LHC and dark matter direct detection experiments. We feature a dark matter candidate which is over 99% bino due to a comparatively large Higgs bilinear mass mu term around the electroweak scale, and hence automatically satisfy the present constraints from the XENON100 and CDMS/EDELWEISS experiments. We do however expect that the continued XENON100 run and extension to 1-ton may begin to probe our model. Similarly, our model is also currently under probe by the LHC through a search for events with ultra-high multiplicity hadronic jets, which are a characteristic feature of the distinctive No-Scale F-SU(5) mass hierarchy.

hep-ph↗

arXiv2012

A Rediatively Light Stop Saves the Best Global Fit for Higgs Boson Mass and Decays

The LHC discovered the Standard Model (SM) like Higgs boson with mass around 125 GeV. However, there exist hints of deviations from Higgs decays. Including the Tevatron data, the deviations can be explained by the extremely mixed stop sector in the sense of best global fit (BGF). We analyze the relations among the competing reduced coupling hGG, Higgs boson mass,and LHC stop mass m_{\wt t_1} lower bound at the tree- and one-loop level. In particular, we point out that we use the light stop running mass in the Higgs boson mass calculation while the light stop pole mass in the Higgs decays. So the gluino radiative correction on the light stop mass plays the crucial role. Its large negative correction saves the GBF in the Minimal Supersymmetric SM (MSSM) and the next to the MSSM (NMSSM) constrained by the perturbativity. Moreover, a light stop is predicted: in the MSSM if we set the gluino mass M_3\lesssim4 TeV, we have m_{\wt t_1}<m_t; while in the NMSSM, imposing the least tuning condition we get m_{\wt t_1}\simeq130 GeV for M_3\simeq1.5 TeV.

hep-ph↗

arXiv2012

Toward the Natural and Realistic NMSSM with and without R-Parity

From the current ATLAS and CMS results on Higgs boson mass and decay rates, the NMSSM is obviously better than the MSSM. To explain the fine-tuning problems such as gauge hiearchy problem and strong CP problem in the SM, we point out that supersymmetry does not need to provide a dark matter candidate, i.e., R-parity can be violated. Thus, we consider three kinds of the NMSSM scenarios: in Scenarios I and II R-parity is conserved and the lightest neutralino relic density is respectively around and smaller than the observed value, while in Scenario III R-parity is violated. To fit all the experimental data, we consider the χ^2 analyses, and find that the Higgs boson mass and decay rates can be explained very well in these Scenarios. Considering the small χ^2 values and fine-tuning around 2-3.7% (or 1-2%), we obtain the viable parameter space with light (or relatively heavy) supersymmetric particle spectra only in Scenario III (or in Scenarios I and II). Because the singlino, Higgsinos, and light stop are relatively light in general, we can relax the LHC supersymmetry search constraints but the XENON100 experiment gives a strong constraint in Scenarios I and II. In all the viable parameter space, the anomalous magnetic moment of the muon (g_μ - 2)/2 are generically small. With R-parity violation, we can increase (g_μ - 2)/2, and avoid the contraints from the LHC supersymmetry searches and XENON100 experiment. Therefore, Scenario III with R-parity violation is more natural and realistic than Scenarios I and II.

hep-ph↗

arXiv2012

Rare B decays in the flip SU(5) Model

In the testable Flipped $SU(5)\times U(1)_X$ model with TeV-scale vector-like particles from F-theory model building dubbed as the flip SU(5) model, we study the vector-like quark contributions to B physics processes, including the quark mass spectra, Feynman rules, new operators and Wilson coefficients, etc. We focus on the implications of the vector-like quark mass scale on B physics. We find that there exists the $\bar{s}bZ$ interaction at tree level, and the Yukawa interactions are changed. Interestingly, different from many previous models, the effects of vector-like quarks on rare B decays such as $B\to X_sγ$ and $B\to X_s\ell^+\ell^-$ do not decouple in some viable parameter space, especially when the vector-like quark masses are comparable to the charged Higgs boson mass. Under the constraints from $B\to X_sγ$ and $\ B\to X_s\ell^+\ell^-$, the latest measurement for $B_s\to μ^+μ^-$ can be explained naturally, and the branching ratio of $B_s\to \ell^+\ell^-γ$ can be up to $(4\sim5)\times10^{-8}$. The non-decouling effects are much more predictable and thus the \fsu5 model may be tested in the near future experiments.

hep-ph↗

arXiv2012

Brightening the (130 GeV) Gamma-Ray Line

The gamma-ray line from dark matter (DM) annihilation is too weak to observe, but its observation will uncover much information, e.g., the DM mass and an nomalously large annihilation rate $\sim0.1$ pb into di-photon. In this work, we construct a minimal effective theory (EFT) incorporating DM and heavier charged particles. A large annihilation rate is obtained from operator coefficients with resonance or strong coupling enhancement. The EFT is stringently constrained by the XENON100 and WMAP data. Without resonance, Dirac DM or colored charged particles are ruled out. It is pointed out that the di-gluon mode may correctly determine the DM relic density. Interestingly, this framework also provides an origin for the Higgs di-photon excess at the LHC\@. We apply the general analysis to the NMSSM, which can elegantly interpret the tentative 130 GeV gamma-ray line. A top-window model is also proposed to explain the gamma-ray line.

hep-ph↗

arXiv2012

Non-trivial Supersymmetry Correlations between ATLAS and CMS Observations

We present definite correlations between the CMS 5 \fb all-hadronic search employing the stransverse mass variable $M_{T2}$ and the ATLAS 5 \fb all-hadronic and multijet supersymmetry (SUSY) searches, suggesting the possibility that both the ATLAS and CMS experiments are already registering a faint but legitimate SUSY signal at the LHC. We isolate this prospective mutual productivity beyond the Standard Model in the framework of the supersymmetric No-Scale Flipped $SU$(5) grand unified theory, supplemented with extra vector-like matter (flippons). Evident overproduction is observed in three CMS \mt2 and four ATLAS hadronic and multijet signal regions, where a \x2 fitting procedure of the CMS 5 \fb \mt2 search establishes a best fit SUSY mass in sharp agreement with corresponding ATLAS searches of equivalently heightened signal significance. We believe this correlated behavior across two distinct experiments at precisely the same SUSY mass scale to be highly non-trivial, and potentially indicative of an existing 5 \fb LHC reach into a pervasive physical supersymmetry framework.

hep-ph↗

arXiv2012

Chanel No5 (fb^-1): The Sweet Fragrance of SUSY

We present compounding evidence of supersymmetry (SUSY) production at the LHC, in the form of correlations between the nominal 5\fb ATLAS and CMS results for the 7 TeV 2011 run and detailed Monte Carlo collider-detector simulation of a concrete supersymmetric model named No-Scale F-SU(5). Restricting analysis to those event selections which yield a signal significance S/sqrt(B+1) greater than 2, we find by application of the χ^2 statistic that strong correlations exist among the individual search strategies and also between the current best fit to the SUSY mass scale and that achieved using historical 1\fb data sets. Coupled with an appropriately large increase in the "depth" of the χ^2 well with increasing luminosity, we suggest that these features indicate the presence of a non-random structure to the data - a light fragrance perhaps evocative of some fuller coming fruition. Those searches having signal significances below 2 are assembled into a lower exclusion bound on the gaugino mass, which is shown to be consistent with the prior best fit. Assuming the forthcoming delivery of an additional tranche of integrated luminosity at 8 TeV during 2012 that measures on the order 15\fb, we project a sufficiency of actionable data to conclusively judge the merits of our proposal.

hep-ph↗

arXiv2012

The Minimal Solution to the mu/B_mu Problem in Gauge Mediation

We provide a minimal solution to the mu/B_mu problem in the gauge mediated supersymmetry breaking by introducing a Standard Model singlet filed S with a mass around the messenger scale which couples to the Higgs and messenger fields. This singlet is nearly supersymmetric and acquires a relatively small Vacuum Expectation Value (VEV) from its radiatively generated tadpole term. Consequently, both mu and B_mu parameters receive the tree-level and one-loop contributions, which are comparable due to the small S VEV. Because there exists a proper cancellation in such two kinds of contributions to B_mu, we can have a viable Higgs sector for electroweak symmetry breaking.

hep-ph↗

arXiv2012

Quaternion-Octonion Unitary Symmetries and Analogous Casimir Operators

An attempt has been made to investigate the global SU(2) and SU(3) unitary flavor symmetries systematically in terms of quaternion and octonion respectively. It is shown that these symmetries are suitably handled with quaternions and octonions in order to obtain their generators, commutation rules and symmetry properties. Accordingly, Casimir operators for SU(2)and SU(3) flavor symmetries are also constructed for the proper testing of these symmetries in terms of quaternions and octonions.

physics.gen-ph↗

arXiv2012

Octonion Quantum Chromodynamics

Starting with the usual definitions of octonions, an attempt has been made to establish the relations between octonion basis elements and Gell-Mann λmatrices of SU(3)symmetry on comparing the multiplication tables for Gell-Mann λmatrices of SU(3)symmetry and octonion basis elements. Consequently, the quantum chromo dynamics (QCD) has been reformulated and it is shown that the theory of strong interactions could be explained better in terms of non-associative octonion algebra. Further, the octonion automorphism group SU(3) has been suitably handled with split basis of octonion algebra showing that the SU(3)_{C}gauge theory of colored quarks carries two real gauge fields which are responsible for the existence of two gauge potentials respectively associated with electric charge and magnetic monopole and supports well the idea that the colored quarks are dyons.

physics.gen-ph↗

arXiv2012

Unification of Dynamical Determination and Bare Minimal Phenomenological Constraints in No-Scale F-SU(5)

We revisit the construction of the viable parameter space of No-Scale F-SU(5), a model built on the F-lipped SU(5)xU(1)_X gauge group, supplemented by a pair of F-theory derived vector-like multiplets at the TeV scale, and the dynamically established boundary conditions of No-Scale Supergravity. Employing an updated numerical algorithm and a substantially upgraded computational engine, we significantly enhance the scope, detail and accuracy of our prior study. We sequentially apply a set of "bare-minimal" phenomenological constraints, consisting of i) the dynamically established boundary conditions of No-Scale Supergravity, ii) consistent radiative electroweak symmetry breaking, iii) precision LEP constraints on the light supersymmetric mass content, iv) the world average top-quark mass, and v) a light neutralino satisfying the 7-year WMAP cold dark matter relic density measurement. The overlap of the viable parameter space with key rare-process limits on the branching ratio for b to s gamma and the muon anomalous magnetic moment is identified as the "golden strip" of F-SU(5). A cross check for top-down theoretical consistency is provided by application of the "Super No-Scale" condition, which dynamically selects a pair of undetermined model parameters in a manner that is virtually identical to the corresponding phenomenological (driven primarily by the relic density) selection. The predicted vector-like particles are candidates for production at the future LHC, which is furthermore sensitive to a distinctive signal of ultra-high multiplicity hadronic jets. The lightest CP-even Higgs boson mass is predicted to be 120+3.5-1 GeV, with an additional 3-4 GeV upward shift possible from radiative loops in the vector-like multiplets. The predominantly bino flavored lightest neutralino is suitable for direct detection by the Xenon collaboration.

hep-ph↗

arXiv2012

A Two-Tiered Correlation of Dark Matter with Missing Transverse Energy: Reconstructing the Lightest Supersymmetric Particle Mass at the LHC

We suggest that non-trivial correlations between the dark matter particle mass and collider based probes of missing transverse energy H_T^miss may facilitate a two tiered approach to the initial discovery of supersymmetry and the subsequent reconstruction of the LSP mass at the LHC. These correlations are demonstrated via extensive Monte Carlo simulation of seventeen benchmark models, each sampled at five distinct LHC center-of-mass beam energies, spanning the parameter space of No-Scale F-SU(5).This construction is defined in turn by the union of the Flipped SU(5) Grand Unified Theory, two pairs of hypothetical TeV scale vector-like supersymmetric multiplets with origins in F-theory, and the dynamically established boundary conditions of No-Scale Supergravity. In addition, we consider a control sample comprised of a standard minimal Supergravity benchmark point. Led by a striking similarity between the H_T^miss distribution and the familiar power spectrum of a black body radiator at various temperatures, we implement a broad empirical fit of our simulation against a Poisson distribution ansatz. We advance the resulting fit as a theoretical blueprint for deducing the mass of the LSP, utilizing only the missing transverse energy in a statistical sampling of >= 9 jet events. Cumulative uncertainties central to the method subsist at a satisfactory 12-15% level. The fact that supersymmetric particle spectrum of No-Scale F-SU(5) has thrived the withering onslaught of early LHC data that is steadily decimating the Constrained Minimal Supersymmetric Standard Model and minimal Supergravity parameter spaces is a prime motivation for augmenting more conventional LSP search methodologies with the presently proposed alternative.

hep-ph↗

arXiv2012

A Higgs Mass Shift to 125 GeV and A Multi-Jet Supersymmetry Signal: Miracle of the Flippons at the \sqrt{s} = 7 TeV LHC

We describe a model named No-Scale F-SU(5) which is simultaneously capable of explaining the dual signals emerging at the LHC of i) a 124-126 GeV Higgs boson mass m_h, and ii) tantalizing low-statistics excesses in the multi-jet data which may attributable to supersymmetry. These targets tend to be mutually exclusive in more conventional approaches. The unified mechanism responsible for both effects is the introduction of a rather unique set of vector-like multiplets at the TeV scale, dubbed flippons, which i) can elevate m_h by around 3-4 GeV via radiative loop corrections, and ii) flatten the running of the strong coupling and color-charged gaugino, resulting in a prominent collider signal from production of light gluino pairs. This well motivated theoretical framework maintains consistency with all key phenomenological constraints, and all residual parameterization freedom may in principle be fixed by a combination of the two experiments described. We project that the already collected luminosity of 5 fb^-1 may be sufficient to definitively establish the status of this model, given appropriate data selection cuts.

hep-ph↗