arXiv subjects

Tianjun Li

Publications and source records attributed to Tianjun Li.

At least 271 records · Page 15Linked to original sources

arXiv2011

Canonical Gauge Coupling Unification in the Standard Model with High-Scale Supersymmetry Breaking

Inspired by the string landscape and the unified gauge coupling relation in the F-theory Grand Unified Theories (GUTs) and GUTs with suitable high-dimensional operators, we study the canonical gauge coupling unification and Higgs boson mass in the Standard Model (SM) with high-scale supersymmetry breaking. In the SM with GUT-scale supersymmetry breaking, we achieve the gauge coupling unification at about 5.3 x 10^{13} GeV, and the Higgs boson mass is predicted to range from 130 GeV to 147 GeV. In the SM with supersymmetry breaking scale from 10^4 GeV to 5.3 x 10^{13} GeV, gauge coupling unification can always be realized and the corresponding GUT scale M_U is from 10^{16} GeV to 5.3 x 10^{13} GeV, respectively. Also, we obtain the Higgs boson mass from 114.4 GeV to 147 GeV. Moreover, the discrepancies among the SM gauge couplings at the GUT scale are less than about 4-6%. Furthermore, we present the SU(5) and SO(10) models from the F-theory model building and orbifold constructions, and show that we do not have the dimension-five and dimension-six proton decay problems even if M_U \le 5 x 10^{15} GeV.

hep-ph↗

arXiv2011

Type IIB Supersymmetric Flux Vacua

On the Type IIB toroidal T^6 orientifolds with generic flux compactifications, we conjecture that in generic supsersymmetric Minkowski vacua, at least one of the flux contributions to the seven-brane and D3-brane tadpoles is positive if the moduli are stabilized properly, and then the tadpole cancellation conditions can not be relaxed. To study the supsersymmetric Minkowski flux vacua, we simplify the fluxes reasonably and discuss the corresponding superpotential. We show that we can not have simultaneously the positive real parts of all the moduli and the negative/zero flux contributions to all the seven-brane and D3-brane tadpoles. Therefore, we can not construct realistic flux models with the relaxed tadpole cancellation conditions. When studying the supsersymmetric AdS vacua, we obtain flux models with the seven-brane and D3-brane tadpole cancellation conditions relaxed elegantly, and we present a semi-realistic Pati-Salam model as well as its particle spectrum. The lifting from the AdS vacua to the Minkowski/dS vacua remains a great challenge in flux model buildings on toroidal orientifolds.

hep-th↗

arXiv2011

Quaternion-Octonion SU(3) Flavor Symmetry

Starting with the quaternionic formulation of isospin SU(2) group, we have derived the relations for different components of isospin with quark states. Extending this formalism to the case of SU(3) group we have considered the theory of octonion variables. Accordingly, the octonion splitting of SU(3) group have been reconsidered and various commutation relations for SU(3) group and its shift operators are also derived and verified for different iso-spin multiplets i.e. I, U and V- spins. Keywords: SU(3), Quaternions, Octonions and Gell Mann matrices PACS NO: 11.30.Hv: Flavor symmetries; 12.10-Dm: Unified field theories and models of strong and electroweak interactions

physics.gen-ph↗

arXiv2011

F-Theory Grand Unification at the Colliders

We predict the exact gaugino mass relation near the electroweak scale at one loop for gravity mediated supersymmetry breaking in F-theory SU(5) and SO(10) models with U(1)_Y and U(1)_{B-L} fluxes, respectively. The gaugino mass relation introduced here differs from the typical gaugino mass relations studied thus far, and in general, should be preserved quite well at low energy. Therefore, these F-Theory models can be tested at the Large Hadron Collider and future International Linear Collider. We present two typical scenarios that satisfy all the latest experimental constraints and are consistent with the CDMS II experiment. In particular, the gaugino mass relation is indeed satisfied at two-loop level with only a very small deviation around the electroweak scale.

hep-ph↗

arXiv2011

The No-Scale Multiverse at the LHC

We present a contemporary perspective on the String Landscape and the Multiverse of plausible string, M- and F-theory vacua, seeking to demonstrate a non-zero probability for the existence of a universe matching our own observed physics within the solution ensemble, arguing for the importance of No-Scale Supergravity as an essential common underpinning. Our context is a highly detailed phenomenological probe of No-Scale F-SU(5), a model representing the intersection of the F-lipped SU(5) X U(1)_X Grand Unified Theory (GUT) with extra TeV-Scale vector-like multiplets derived out of F-theory, and the dynamics of No-Scale Supergravity. We present a highly constrained "Golden" region with tan(beta) \sim 15, m_t = 173.0 - 174.4 GeV, M_1/2 = 455 - 481 GeV, and M_V = 691 - 1020 GeV, which simultaneously satisfies all known experimental constraints. We supplement this bottom-up phenomenological perspective with a top-down theoretical analysis of the one-loop effective Higgs potential, achieving a striking consonance via the dynamic determination of tan(beta) and M_1/2 at the local secondary minimization of the spontaneously broken electroweak Higgs vacuum V_min. We present the distinctive signatures of No-Scale F-SU(5) at the LHC, where a light stop and gluino are expected to generate a surplus of ultra-high multiplicity (>= 9) hadronic jet events. We propose modest alterations to the canonical background selection cut strategy which would enhance resolution of these events, while readily suppressing the contribution of all Standard Model processes, and allowing a clear differentiation from competing models of new physics. Detection by the LHC of the ultra-high jet signal would constitute a suggestive evocation of the intimately linked stringy origins of F-SU(5), and could provide a glimpse into the fundamental string moduli, and possibly even the workings of the No-Scale Multiverse.

hep-ph↗

arXiv2011

Elements of F-ast Proton Decay

Gauge coupling unification in the Minimal Supersymmetric Standard Model (MSSM) strongly suggests the existence of a Grand Unified Theory (GUT), which could be probed by the observation of proton decay. Proton lifetime in the p \to (e+|mu+) pi0 dimension six mode is proportional in the fourth power to the GUT mass scale, and inversely proportional in the fourth power to the GUT coupling. We provide an updated dictionary of solutions for the relevant unification parameters with generic beta-function coefficients, significantly upgrading the level of detail with which second order effects are treated, and correcting subtle published errors. F-lipped SU(5) with strict MSSM field content is known to survive existing null detection limits for proton decay approaching 10^34 years, and indeed, the lifetime predicted by prior studies can be so long that successful detection is not currently plausible. Recently studied classes of F-theory derived GUT models postulate additional vector-like multiplets at the TeV scale which modify the renormalization group to yield a substantial increase in the SU(3)_C X SU(2)_L unified coupling. We find the conjunction of these models with the F-resh analysis employed to be comparatively F-ast proton decay, only narrowly evading existing detection limits, and likely falling within the observable range of proposed next generation detectors such as DUSEL and Hyper-Kamiokande. The TeV-scale vector multiplets are themselves suitable for cross correlation by the Large Hadron Collider. Their presence moreover magnifies the gap between the dual mass scales of Flipped SU(5), allowing for an elongated second stage renormalization, pushing grand unification to the doorstep of the reduced Planck mass.

hep-ph↗

arXiv2011

The Golden Strip of Correlated Top Quark, Gaugino, and Vectorlike Mass In No-Scale, No-Parameter F-SU(5)

We systematically establish the hyper-surface within the tan(beta), top quark mass m_t, universal gaugino mass M_1/2, and vectorlike mass M_V parameter volume which is compatible with the application of the No-Scale Supergravity boundary conditions, particularly the vanishing of the Higgs bilinear soft term B_mu, near to the Planck mass at the point M_F of ultimate F-lipped SU(5) unification. M_F is elevated from the penultimate partial unification near the traditional GUT scale at a mass M_32 by the inclusion of extra F-theory derived heavy vectorlike multiplets. We demonstrate that simultaneous adherence to all current experimental constraints, most importantly contributions to the muon anomalous magnetic moment (g-2)_mu, the branching ratio limit on (b \to s gamma), and the 7-year WMAP relic density measurement, dramatically reduces the allowed solutions to a highly non-trivial "golden strip" with tan(beta) \sim 15, m_t = 173.0-174.4 GeV, M_1/2 = 455-481 GeV, and M_V = 691-1020 GeV, effectively eliminating all extraneously tunable model parameters. We emphasize that the consonance of the theoretically viable m_t range with the experimentally established value is an independently correlated "postdiction". The predicted range of M_V is testable at the Large Hadron Collider (LHC). The partial lifetime for proton decay in the leading (e+|mu+) pi0 channels falls around 4.6 X 10^34 Y, testable at the future DUSEL and Hyper-Kamiokande facilities.

hep-ph↗

arXiv2011

MSSM-like AdS Flux Vacua with Frozen Open-string Moduli

We construct supersymmetric Pati-Salam flux vacua in AdS from intersecting D6-branes on T^6/(Z_2 x Z_2'). The models constructed have three generations of MSSM matter plus right-handed neutrinos. Because the cycles wrapped by the D-branes are rigid there are no extra massless fields in the adjoint representation, arising as open-string moduli. However, we find that it is problematic to break the Pati-Salam gauge symmetry to the Standard Model (SM) while keeping the SM hypercharge massless.

hep-th↗

arXiv2011

The Ultra-High Jet Multiplicity Signal of Stringy No-Scale F-SU(5) at the \sqrt{s} = 7 TeV LHC

We present the distinctive collider signatures of No-Scale F-SU(5), a highly efficient and phenomenologically favored model built on the tripodal foundations of the F-lipped SU(5) X U(1)_X Grand Unified Theory, extra F-theory derived TeV scale vector-like particle multiplets, and the dynamic high scale boundary conditions of No-Scale Supergravity. The identifying features of the supersymmetric spectrum are a light stop and gluino, with both sparticles much lighter than all the additional squarks. This unique mass hierarchy leads to the enhanced production of events with an ultra-high multiplicity of hadronic jets which should be clearly visible to the \sqrt{s} = 7 TeV LHC at only 1 inverse fb of integrated luminosity. We suggest a modest alternative event cutting procedure based around a reduced minimal transverse momentum per jet (p_T > 20 GeV), and an increased minimal multiplicity (>= 9) of distinct jets per subscribed event. These criteria optimize the F-SU(5) signal to background ratio, while readily suppressing the contribution of all Standard Model processes, allowing moreover a clear differentiation from competing models of new physics, most notably minimal supergravity. The characteristic No-Scale signature is quite stable across the viable parameter space, modulo an overall rescaling of the mass spectrum; Detection by the LHC of the ultra-high jet signal would constitute a suggestive evocation of the intimately linked stringy origins of F-SU(5), and could possibly provide a glimpse into the underlying structure of the fundamental string moduli.

hep-ph↗

arXiv2011

Ultra High Jet Signals from Stringy No-Scale Supergravity

We present distinctive signatures of flipped F-Theory models with TeV-scale vector-like particles, a \sqrt{s} = 7 TeV 1 fb^{-1} test at LHC of a class of models well-motivated from string theory. The characteristic feature is a light stop and gluino, both sparticles lighter than all other squarks. This unique aspect of the supersymmetry spectrum generates an ultra-high multiplicity of hadronic jets. We find the optimal signal to background ratio is realized for 9 or more jets. Exclusion of the essential cuts presented here could leave the ultra-high jet signal severely attenuated and concealed.

hep-ph↗

arXiv2011

The Golden Point of No-Scale and No-Parameter ${\cal F}$-SU(5)

The ${\cal F}$-lipped $SU(5)\times U(1)_X$ Grand Unified Theory (GUT) supplemented by TeV-scale vector-like particles from ${\cal F}$-theory, together dubbed ${\cal F}$-SU(5), offers a natural multi-phase unification process which suggests an elegant implementation of the No-Scale Supergravity boundary conditions at the unification scale $M_{\cal F} \simeq 7 \times 10^{17}$ GeV. Enforcing the No-Scale boundary conditions, including $B_μ(M_{\cal F})=0$ on the Higgs bilinear soft term, with the precision 7-year WMAP value on the dark matter relic density isolates a highly constrained "golden point" located near $M_{1/2} = 455$ GeV and $\tan β= 15$ in the $\tanβ-M_{1/2}$ plane, which simultaneously satisfies all known experiments, and moreover corresponds to an imminently observable proton decay rate. Because the universal gaugino mass is actually determined from established low energy data via Renormalization Group Equation (RGE) running, there are no surviving arbitrary scale parameters in the present model.

hep-ph↗

arXiv2011

Dark Matter, Proton Decay and Other Phenomenological Constraints in ${\cal F}$-SU(5)

We study gravity mediated supersymmetry breaking in ${\cal F}$-SU(5) and its low-energy supersymmetric phenomenology. The gaugino masses are not unified at the traditional grand unification scale, but we nonetheless have the same one-loop gaugino mass relation at the electroweak scale as minimal supergravity (mSUGRA). We introduce parameters testable at the colliders to measure the small second loop deviation from the mSUGRA gaugino mass relation at the electroweak scale. In the minimal SU(5) model with gravity mediated supersymmetry breaking, we show that the deviations from the mSUGRA gaugino mass relations are within 5%. However, in ${\cal F}$-SU(5), we predict the deviations from the mSUGRA gaugino mass relations to be larger due to the presence of vector-like particles, which can be tested at the colliders. We determine the viable parameter space that satisfies all the latest experimental constraints and find it is consistent with the CDMS II experiment. Further, we compute the cross-sections of neutralino annihilations into gamma-rays and compare to the first published Fermi-LAT measurement. Finally, the corresponding range of proton lifetime predictions is calculated and found to be within reach of the future Hyper-Kamiokande and DUSEL experiments.

hep-ph↗

arXiv2011

Semi-direct Gauge-Yukawa Mediation

We propose semi-direct Gauge-Yukawa mediation of supersymmetry (SUSY) breaking. The messenger fields mediating SUSY breaking to the visible sector do not directly couple with the goldstino field, and instead they have gauge and Yukawa interactions with some primary messenger fields which couple directly with the goldstino fields. From the explicit Feynman diagram calculations for the SUSY breaking soft masses, we find that the SUSY particle spectra can be realistic. Especially, this generalization of semi-direct gauge mediation solves the massless gaugino mass problem since the holomorphic soft mass terms of the messenger fields can be generated by Yukawa couplings. We also provide some arguments that this scenario can be realized naturally in some dynamical SUSY-breaking models such as the ISS-like model.

hep-ph↗

arXiv2011

Realistic Standard Model Fermion Mass Relations in Generalized Minimal Supergravity (GmSUGRA)

Grand Unified Theories (GUTs) usually predict wrong Standard Model (SM) fermion mass relation m_e/m_μ = m_d/m_s toward low energies. To solve this problem, we consider the Generalized Minimal Supergravity (GmSUGRA) models, which are GUTs with gravity mediated supersymmetry breaking and higher dimensional operators. Introducing non-renormalizable terms in the super- and Kähler potentials, we can obtain the correct SM fermion mass relations in the SU(5) model with GUT Higgs fields in the {\bf 24} and {\bf 75} representations, and in the SO(10) model. In the latter case the gauge symmetry is broken down to SU(3)_C X SU(2)_L X SU(2)_R X U(1)_{B-L}, to flipped SU(5)X U(1)_X, or to SU(3)_C X SU(2)_L X U(1)_1 X U(1)_2. Especially, for the first time we generate the realistic SM fermion mass relation in GUTs by considering the high-dimensional operators in the Kähler potential.

hep-ph↗

arXiv2011

SU(7) Unification of SU(3)_CSU(4)_W U(1)_{B-L}

We propose the SUSY SU(7) unification of the SU(3)_C* SU(4)_W* U(1)_{B-L} model. Such unification scenario has rich symmetry breaking chains in a five-dimensional orbifold. We study in detail the SUSY SU(7) symmetry breaking into SU(3)_C* SU(4)_W* U(1)_{B-L} by boundary conditions in a Randall-Sundrum background and its AdS/CFT interpretation. We find that successful gauge coupling unification can be achieved in our scenario. Gauge unification favors low left-right and unification scales with tree-level \sin^2θ_W=0.15. We use the AdS/CFT dual of the conformal supersymmetry breaking scenario to break the remaining N=1 supersymmetry. We employ AdS/CFT to reproduce the NSVZ formula and obtain the structure of the Seiberg duality in the strong coupling region for 3/2N_c<N_F<3N_C. We show that supersymmetry is indeed broken in the conformal supersymmetry breaking scenario with a vanishing singlet vacuum expectation value.

hep-ph↗

arXiv2010

Fast Proton Decay

We consider proton decay in the testable flipped SU(5) X U(1)_X models with TeV-scale vector-like particles which can be realized in free fermionic string constructions and F-theory model building. We significantly improve upon the determination of light threshold effects from prior studies, and perform a fresh calculation of the second loop for the process p \to e^+ π^0 from the heavy gauge boson exchange. The cumulative result is comparatively fast proton decay, with a majority of the most plausible parameter space within reach of the future Hyper-Kamiokande and DUSEL experiments. Because the TeV-scale vector-like particles can be produced at the LHC, we predict a strong correlation between the most exciting particle physics experiments of the coming decade.

hep-ph↗

arXiv2010

Supersymmetry Breaking Scalar Masses and Trilinear Soft Terms in Generalized Minimal Supergravity

In the generalized minimal supergravity (GmSUGRA) scenario, we systematically study the supersymmetry breaking scalar masses, Standard Model fermion Yukawa coupling terms, and trilinear soft terms in SU(5) models with the Higgs fields in the {\bf 24} and {\bf 75} representations, and in SO(10) models where the gauge symmetry is broken down to the Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R gauge symmetry, SU(3)_C X SU(2)_L X SU(2)_R X U(1)_{B-L} gauge symmetry, George-Glashow SU(5) X U(1)' gauge symmetry, flipped SU(5) X U(1)_X gauge symmetry, and SU(3)_C X SU(2)_L X U(1)_1 X U(1)_2 gauge symmetry. Most importantly, we for the first time consider the scalar and gaugino mass relations, which can be preserved from the unification scale to the electroweak scale under one-loop renormalization group equation running, in the SU(5) models, the Pati-Salam models and flipped SU(5) X U(1)_X models arising from SO(10) models. With such interesting relations, we may distinguish the minimal supergravity (mSUGRA) and GmSUGRA scenarios if the supersymmetric particle spectrum can be measured at the LHC and ILC. Thus, it provides us with another important window of opportunity at the Planck scale.

hep-ph↗

arXiv2010

Generalizing Minimal Supergravity

In Grand Unified Theories (GUTs), the Standard Model (SM) gauge couplings need not be unified at the GUT scale due to the high-dimensional operators. Considering gravity mediated supersymmetry breaking, we study for the first time the generic gauge coupling relations at the GUT scale, and the general gaugino mass relations which are valid from the GUT scale to the electroweak scale at one loop. We define the index k for these relations, which can be calculated in GUTs and can be determined at the Large Hadron Collider and the future International Linear Collider. Thus, we give a concrete definition of the GUT scale in these theories, and suggest a new way to test general GUTs at future experiments. We also discuss five special scenarios with interesting possibilities. With our generic formulae, we present all the GUT-scale gauge coupling relations and all the gaugino mass relations in the SU(5) and SO(10) models, and calculate the corresponding indices k. Especially, the index k is 5/3 in the traditional SU(5) and SO(10) models that have been studied extensively so far. Furthermore, we discuss the field theory realization of the U(1) flux effects on the SM gauge kinetic functions in F-theory GUTs, and calculate their indices k as well.

hep-ph↗