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Tianjun Li

Publications and source records attributed to Tianjun Li.

354 records · Page 20Linked to original sources
arXiv2001

CP Violation and Extra Dimensions

It is shown that the new sources of CP violation can be generated in the models with more than one extra dimensions. In the supersymmetric models on the space-time $M^4\times T^2/Z_2$, where the radius moduli have auxiliary vacuum expectation values and the supersymmetry breaking is mediated by the Kaluza-Klein states of gauge supermultiplets, we analyze the gaugino masses and trilinear couplings for two scenarios and obtain that there exist relative CP violating phases among the gaugino masses and trilinear couplings.

hep-ph↗
arXiv2000

Brane Networks in AdS Space

We present static solutions to Einstein's equations corresponding to the most general network of $N$ orthogonal families of $(2+N)$-branes in $(4+N)$-dimensional $AdS$ spacetimes. The bulk cosmological constant can take a different value in each cell enclosed by intersecting branes and the extra dimensions can be compact or noncompact. In each family of branes the inter-brane spacing is arbitrary. The extra dimensions may be any or all of the manifolds, $R^1$, $R^1/Z_2$, $S^1$ and $S^1/Z_2$. Only when the extra dimensions are $R^1$ or/and $R^1/Z_2$, can networks consisting solely of positive tension branes be constructed. Such configurations may find application in models with localized gravity and symmetry breaking by shining.

hep-th↗
arXiv2000

Classification of 5-Dimensional Space-Time with Parallel 3-Branes

If the fifth dimension is one-dimensional connected manifold, up to diffeomorphic, the only possible space-time will be $M^4 \times R^1$, $M^4 \times R^1/Z_2$, $M^4 \times S^1$ and $M^4 \times S^1/Z_2$. And there exist two possibilities on cosmology constant along the fifth dimension: the cosmology constant is constant, and the cosmology constant is sectional constant. We construct the general models with parallel 3-branes and with constant/sectional constant cosmology constant along the fifth dimension on those kinds of the space-time, and point out that for compact fifth dimension, the sum of the brane tensions is zero, for non-compact fifth dimension, the sum of the brane tensions is positive. We assume the observable brane which includes our world should have positive tension, and obtain that the gauge hierarchy problem can be solved in those scenarios. We also discuss some simple models.

hep-th↗
arXiv2000

Non-Compact $AdS_5$ Universe with Parallel Positive Tension 3-Branes

We construct the general model with only parallel positive tension 3-branes on $M^4 \times R^1$ and $M^4 \times R^1/Z_2$. The cosmology constant is sectional constant along the fifth dimension. In this general scenario, the 5-dimensional GUT scale on each brane can be indentified as the 5-dimensional Planck scale, but, the 4-dimensional Planck scale is generated from the low 4-dimensional GUT scale exponentially in our world. We also give two simple models to show explicitly how to solve the gauge hierarchy problem.

hep-th↗
arXiv1999

Scale, Gauge Couplings, Soft Terms and Toy Compactification in M-theory on $S^1/Z_2$

In M-theory on $S^1/Z_2$, we point out that to be consistant, we should keep the scale, gauge couplings and soft terms at next order, and obtain the soft term relations: $M_{1/2} = -A$, $|{M_{0}/{M_{1/2}}}| \leq {1/{\sqrt 3}}$ in the standard embedding and $M_{1/2}=-A$ in the non-standard embedding with five branes and $K_{5,n}=0$. We construct a toy compactification model which includes higher order terms in 4-dimensional Lagrangian in standard embedding, and discuss its scale, gauge couplings, soft terms, and show that the higher order terms do affect the scale, gauge couplings and especially the soft terms if the next order correction was not small. We also construct a toy compactification model in non-standard embedding with five branes and discuss its phenomenology. We argue that one might not push the physical Calabi-Yau manifold's volume to zero at any point along the eleventh dimension.

hep-th↗
arXiv1999

Gauge Hierarchy from $AdS_5$ Universe with 3-Branes

If the universe is (or a slice of) $AdS_5$ space with 3-branes, the 5-dimensional GUT scale on each brane can be indetified as the 5-dimensional Planck scale, but, the 4-dimensional Planck scale is generated from the low 4-dimensional GUT scale exponentially in our world. The 4-dimensional GUT scales and Planck scale are related to the 5-dimensional GUT scales and Planck scale by exponential factors, respectively. One of such scenarios was suggested by Randall and Sundrum recently. We give another scenario that the 4-dimensional Planck scale is generated from the low five-dimensional Planck scale by an exponential hierarchy, and the mass scale in the Standard Model is not rescaled from the 5-dimensional metric to the 4-dimensional metric. We also argue that the additional constant in the solution might exist, which will rescale the 5-dimensional Planck scale and affect the physical scale picture. Finally, we embed those compactifications to the general compactification on $AdS_5$ space and discuss the origin of the additional constant.

hep-th↗
arXiv1999

Phenomenology Remarks in M-theory on $S^1/Z_2$

In the simplest compactification, we discuss the intermediate unification in M-theory on $S^1/Z_2$, and point out that we can push the eleven dimension Planck scale to the TeV range if the gauge coupling in the hidden sector is super weak, and the particles in the hidden sector might become candidates of dark matter. We also discuss the soft terms in non-standard embedding. To the next leading order, we compactify the perfect square and calculate the gravitino mass. Furthermore, we give the general Kähler potential, gauge kinetic function and superpotential if the next order correction is very large, i. e., ${{αT}\over S}$ is close to 1.

hep-ph↗
arXiv1999

Scales, Couplings Revisited and Low Energy Phenomenology in M-theory on $S^1/Z_2$

We revisit the eleven dimension Planck scale, the physical scale of the eleventh dimension, the physical scale of Calabi-Yau manifold and coupling in hidden sector in M-theory on $S^1/Z_2$. And we discuss the reasonable bound on them. Considering F-term of dilaton and moduli SUSY breaking and choosing two repersentative points which correspond to scalar quasi-massless scenario and dilaton dominant SUSY breaking scenario respectively, we analyze experimental constraints to the parameter space. The sparticle spectrum and some phenomenological predictions are also given.

hep-ph↗
arXiv1998

Trilepton Signal of Minimal Supergravity at the Tevatron Including $τ$-lepton Contributions

The trilepton signal with missing transverse energy ($3\ell+\notE_T$, with $\ell = e$ or $μ$) from chargino-neutralino ($χ^\pm_1 χ^0_2$) associated production and decays is studied for the upgraded Fermilab Tevatron Collider with 2 TeV center of mass energy and integrated luminosity of 2 fb$^{-1}$ (MI) to 20 fb$^{-1}$ (TeV33). In some regions of parameter space in the minimal supergravity model, $χ^\pm_1$ and $χ^0_2$ decay dominantly into final states with $τ$ leptons via real or virtual $\tildeτ_1$ sleptons. The contributions from $τ-$leptonic decays increase the trilepton signal from $χ^\pm_1 χ^0_2$ by at least a factor of two when soft but realistic cuts on lepton transverse momenta are used. With the Main Injector, a trilepton signal can be detected at $\tanβ\equiv v_2/v_1 \sim 3$ for universal masses $m_{1/2}, m_0 \alt$ 200 GeV.

hep-ph↗
arXiv1998

Soft Terms in M-theory

We discuss dilaton and Moduli dominant SUSY breaking scenarios in M-theory. In addition, for the nonperturbative superpotential from gaugino condensation, we discuss the soft terms in the simplest model (only S and T moduli fields) and in the $T^6/Z_{12}$ model from M-theory. From the phenomenology consideration, we suggest massless scalar SUSY breaking scenario.

hep-ph↗
arXiv1998

Compactification and Supersymmetry Breaking in M-theory

Keeping N=1 supersymmetry in 4-dimension and in the leading order, we disuss the various orbifold compactifications of M-theory suggested by Horava and Witten on $T^6/Z_3$, $T^6/Z_6$, $T^6/Z_{12}$, and the compactification by keeping singlets under $SU(2)\times U(1)$ symmetry, then the compactification on $S^1/Z_2$. We also discuss the next to leading order Kähler potential, superpotential, and gauge kinetic function in the $Z_{12}$ case. In addition, we calculate the SUSY breaking soft terms and find out that the universality of the scalar masses will be violated, but the violation might be very small.

hep-th↗