arXiv subjects

Tianjun Li

Publications and source records attributed to Tianjun Li.

At least 109 records · Page 6Linked to original sources

arXiv2020

Uncovering quirk signal via energy loss inside tracker

The quirk particle carries Lorentz force and long-range infracolor force, while suffers relatively large ionization energy loss inside the detector. It can be indirectly constrained by mono-jet search or directly search through co-planar hits if the confinement scale is not too low ($Λ\gtrsim 100$ eV). Considering the ionization energy loss inside tracker, we improve the co-planar search. We also will solve the equation of motion for quirks numerically by including all of the important contributions. Based on our selection strategy, the $\sim 100$ fb$^{-1}$ dataset at the LHC will be able to probe the colored fermion/scalar quirks with masses up to {2.1/1.1 TeV}, and the color neutral fermion/scalar quirks with masses up to {450/150 GeV}, respectively.

hep-ph↗

arXiv2020

Helical phase inflation and its observational constraints

We consider a class of helical phase inflation models from the ${\mathcal N}=1$ supergravity where the phase component of a complex field acts as an inflaton. This class of models avoids the eta problem in supergravity inflation due to the phase monodromy of the superpotential. We study the inflationary predictions of this class of models in the context of both standard and large extra dimensional brane cosmology, and find that they can easily accommodate the Planck 2018 and BICEP2 constraints. We find that the helical phase inflation has $α$-attractors and the attractors depend on one model parameter only.

hep-ph↗

arXiv2020

Probing the Supersymmetric Grand Unified Theories at the Future Proton-Proton Colliders and Hyper-Kamiokande Experiment

Gauge coupling unification in the Supersymmetric Standard Models strongly implies the Grand Unified Theories (GUTs). With the grand desert hypothesis, we show that the supersymmetric GUTs can be probed at the future proton-proton (pp) colliders and Hyper-Kamiokande experiment. For the GUTs with the GUT scale $M_{GUT} \le 1.0\times 10^{16}$ GeV, we can probe the dimension-six proton decay via heavy gauge boson exchange at the Hyper-Kamiokande experiment. Moreover, for the GUTs with $M_{GUT} \ge 1.0\times 10^{16}$ GeV, we for the first time study the upper bounds on the gaugino and sfermion masses. We show that the GUTs with anomaly and gauge mediated supersymmetry breakings are well within the reaches of the future 100 TeV pp colliders such as the ${\rm FCC}_{\rm hh}$ and SppC, and the supersymmetric GUTs with gravity mediated supersymmetry breaking can be probed at the future 160 TeV pp collider.

hep-ph↗

arXiv2020

The quirk trajectory

We for the first time obtain the analytical solution for the quirk equation of motion in an approximate way. Based on it, we study several features of quirk trajectory in a more precise way, including quirk oscillation amplitude, number of periods, as well as the thickness of quirk pair plane. Moreover, we find an exceptional case where the quirk crosses at least one of the tracking layers repeatedly. Finally, we consider the effects of ionization energy loss and fixed direction of infracolor string for a few existing searches.

hep-ph↗

arXiv2020

The KSVZ Axion and Pseudo-Nambu-Goldstone Boson Models for the XENON1T Excess

The XENON1T excess can be explained by the Axion Like Particle (ALP) dark matter with mass around 2.5 keV. However, there are three problems needed to be solved: suppressing the coupling $g_{aγ}$ between the ALP and photon, and generating the proper coupling $g_{ae}$ between the ALP and electron as well as the correct ALP mass. We propose three models to solve these problems. In our models, the $g_{ae}$ couplings are produced by integrating out the vector-like leptons, and the correct ALP masses arise from high-dimensional operators. In the KSVZ axion model, the coupling $g_{aγ}$ can be suppressed by choosing proper sets of vector-like fermions, but we need some fine-tunings to obtain the ALP mass. Similarly, one can study the DFSZ axion model. In the $Z_8$ and $ U(1)_X$ models with approximate Pseudo-Nambu-Goldstone Bosons (PNGBs), the coupling $g_{aγ}$ is suppressed due to $SU(3)_C \times U(1)_{\rm EM}$ anomaly free. In the $Z_8$ model, the PNGB mass can be generated naturally at the keV scale via the dimension-8 operator. To solve the PNGB quality problem in the $ Z_8$ model, we embed it into the model with $ U(1)_X$ gauge symmetry.

hep-ph↗

arXiv2020

Revisiting the Supersymmetric Pati-Salam Models from Intersecting D6-branes

Employing new scanning methods, we revisit the systematic construction of three-family $N=1$ supersymmetric Pati-Salam models in Type IIA orientifolds on ${\bf T}^6/(\mathbb Z_2\times \mathbb Z_2)$ with intersecting D6-branes. Arising from the stacks of D6-branes with $U(n)$ gauge symmetries, the Pati-Salam gauge symmetries $SU(4)_C\times SU(2)_L \times SU(2)_R$ can be broken down to the Standard Model via D-brane splitting as well as D- and F-flatness preserving Higgs mechanism. Also, the hidden sector contains $USp(n)$ branes, which are parallel with the orientifold planes or their ${\mathbb Z_2}$ images. We find that the Type II T-duality in the previous study is not an equivalent relation in Pati-Salam model building if the model is not invariant under $SU(2)_L$ and $SU(2)_R$ exchange, and provides a way to obtain new models. We systematically construct the new models with three families, which usually do not have gauge coupling unification at the string scale. We for the first time construct the Pati-Salam models with one wrapping number equal to $5$. In particular, we find that these models carry more refined gauge couplings, and thus with more possibility to have approximate gauge coupling unification.

hep-th↗

arXiv2020

Generalized Supersymmetric Pati-Salam Models from Intersecting D6-branes

Following the scanning methods of arXiv:1910.04530, we for the first time systematically construct the $N=1$ supersymmetric $SU(12)_C\times SU(2)_L\times SU(2)_R$ models, $SU(4)_C\times SU(6)_L\times SU(2)_R$ models, and $SU(4)_C\times SU(2)_L\times SU(6)_R$ models from the Type IIA orientifolds on $\bf T^6/(\mathbb Z_2\times \mathbb Z_2)$ with intersecting D6-branes. These gauge symmetries can be broken down to the Pati-Salam gauge symmetry $SU(4)_C\times SU(2)_L \times SU(2)_R$ via three $SU(12)_C/SU(6)_L/SU(6)_R$ adjoint representation Higgs fields, and further down to the Standard Model (SM) via the D-brane splitting and Higgs mechanism. Also, we obtain three families of the SM fermions, and have the left-handed and right-handed three-family SM fermion unification in the $SU(12)_C\times SU(2)_L\times SU(2)_R$ models, the left-handed three-family SM fermion unification in the $SU(4)_C\times SU(6)_L\times SU(2)_R$ models, and the right-handed three-family SM fermion unification in the $SU(4)_C\times SU(2)_L\times SU(6)_R$ models. Moreover, the $SU(4)_C\times SU(6)_L\times SU(2)_R$ models and $SU(4)_C\times SU(2)_L\times SU(6)_R$ models are related by the left and right gauge symmetry exchanging, as well as a variation of type II T-duality. Furthermore, the hidden sector contains $USp(n)$ branes, which are parallel with the orientifold planes or their $Z_2$ images and might break the supersymmetry via gaugino condensations.

hep-th↗

arXiv2020

Isospin-Violating Dark Matter in the $U(1)'$ Model with $E_6$ Origin

We propose a $U(1)'$ model from $E_6$ which has an isospin-violation dark matter. By choosing a proper linear combination of two extra $U(1)$ gauge symmetries in $E_6$, it is natural to realize the ratio $f_n/f_p=-0.7$ so as to maximally relax the constraints from the Xenon based direct detection experiments. We study the sensitivities of the dark matter direct and indirect detection experiments, and identify the parameter spaces that can give the observed relic density. We also study the sensitivities of the future colliders with center mass energy $\sqrt{s}$= 33/50/100 TeV, and compare the different detection methods. We show that in some parameter spaces the future colliders can give much stronger limits.

hep-ph↗

arXiv2019

$(g-2)_{μ,e}$ and the ANITA anomalous events in a three-loop neutrino mass model

The most recent measurement of the fine structure constant leads to a 2.4 $σ$ deviation in the electron anomalous magnetic moment $g_{e}$-2, while the muon anomalous magnetic moment $g_μ$-2 has a long standing 3.7 $σ$ deviation in the opposite direction. We show that these deviations can be explained in a three-loop neutrino mass model based on an $E_6$ Grand Unified Theory. We also study the impact such a model can have on the anomalous events observed by the ANITA experiment and find an insufficient enhancement of the event rate.

hep-ph↗

arXiv2019

The Heavy Gluino in Natural No-Scale $\cal{F}$-$SU$(5)

In light of recent 80-137 $\rm{fb}^{-1}$ results at the LHC Run 2 establishing a lower gluino mass limit of 2.25 TeV, we revisit the supersymmetric GUT model Flipped $SU$(5) with extra vector-like particles, known as $\cal{F}$-$SU$(5), with vanishing No-Scale Supergravity boundary conditions at the string scale of about $2 \times 10^{17}$ GeV, including the supersymmetry breaking $B_μ$ parameter which is strictly enforced as $B_μ = 0$. Given the proportional dependence of all model scales on a single parameter $M_{1/2}$, No-Scale $\cal{F}$-$SU$(5) was shown to possess no electroweak fine-tuning and thus persists as a $natural$ one-parameter model. In this fresh analysis here, we demand consistency with the measured 125 GeV light Higgs boson mass, though we forgo an upper limit on the lightest neutralino relic density. The resulting phenomenology delivers a gluino mass of $M(\widetilde{g}) \lesssim 7.5$ TeV and a lightest supersymmetric particle (LSP) of $M(\widetildeχ_1^0) \lesssim 1.6$ TeV. In order to dilute the relic density down to the WMAP and Planck measurements, we rely upon a single cosmological master coupling $λ_6$.

hep-ph↗

arXiv2019

Naturalness in D-brane Inspired Models

We examine the naturalness of the D-brane inspired model constructed in flipped $SU(5)$ supplemented with vector-like particles at the TeV scale, dubbed flippons. We find the model can produce a mainly Higgsino-like lightest supersymmetric particle (LSP) and small light stops, as favored by naturalness. In fact, a large trilinear scalar $A_t$ term at the electroweak (EW) scale creates a large mass splitting between the top squarks, driving the light stop to near degeneracy with an LSP that is almost all Higgsino, with $ΔM(\widetilde{t}_1, \widetildeχ_1^0) < 5$ GeV, evading the LHC constraint on $\widetilde{t}_1 \to c \widetildeχ_1^0$ thus far. Given the smallness of the light stop, generating a 125 GeV light Higgs boson mass is aided by one-loop contributions from the Yukawa couplings between the flippons and Higgs fields. The resulting parameter space satisfying naturalness is rather constrained, thus we assess its viability by means of comparison to the LHC constraint on soft charm jets and direction detection limits on spin-independent cross-sections. Finally, we compute the level of electroweak fine-tuning and uncover a region with $Δ_{EW} < 30$, $i.e.$, fine-tuning better than 3%, regarded as low electroweak fine-tuning. Given the small light stop, the electroweak fine-tuning from only the top squarks is of $\cal{O}$(1), indicating no fine-tuning from neither the light stop $\widetilde{t}_1$ nor the heavy stop $\widetilde{t}_2$.

hep-ph↗

arXiv2019

Three-loop neutrino masses via new massive gauge bosons from $E_6$ GUT

We propose an $SU(3)_C\times SU(2)_L \times SU(2)_N \times U(1)_Y$ model arising from $E_6$ grand unified theory. We show that the tiny neutrino masses in this model can be generated at the three-loop involving the $SU(2)_N$ gauge bosons. With Yukawa couplings around 0.01 or larger and TeV-scale $SU(2)_N$ gauge bosons, we show that the neutrino oscillation data can be explained naturally by presenting a concrete benchmark set of input parameters. All new particles are around the TeV scale. Thus our model can be tested at the ongoing/future collider experiments.

hep-ph↗

arXiv2019

The simple interpretations of lepton anomalies in the lepton-specific inert two-Higgs-doublet model

There exist about $3.7σ$ positive and $2.4σ$ negative deviations in the muon and electron anomalous magnetic moments ($g-2$). Also, some ratios for lepton universality in $τ$ decays have almost $2σ$ deviations from the Standard Model. In this paper, we propose a lepton-specific inert two-Higgs-doublet model. After imposing all the relevant theoretical and experimental constraints, we show that these lepton anomalies can be explained simultaneously in many parameter spaces with $m_H > 200$ GeV and $m_A~(m_{H^\pm})> 500$ GeV for appropriate Yukawa couplings between leptons and inert Higgs. The key point is that these Yukawa couplings for $μ$ and $τ$/$e$ have opposite sign.

hep-ph↗

arXiv2019

A simple and natural interpretations of the DAMPE cosmic-ray electron/positron spectrum within two sigma deviations

The DArk Matter Particle Explorer (DAMPE) experiment has recently announced the first results for the measurement of total electron plus positron fluxes between 25 GeV and 4.6 TeV. A spectral break at about 0.9 TeV and a tentative peak excess around 1.4 TeV have been found. However, it is very difficult to reproduce both the peak signal and the smooth background including spectral break simultaneously. We point out that the numbers of events in the two energy ranges (bins) close to the 1.4 TeV excess have $1σ$ deficits. With the basic physics principles such as simplicity and naturalness, we consider the $-2σ$, $+2σ$, and $-1σ$ deviations due to statistical fluctuations for the 1229.3~GeV bin, 1411.4~GeV bin, and 1620.5~GeV bin. Interestingly, we show that all the DAMPE data can be explained consistently via both the continuous distributed pulsar and dark matter interpretations, which have $χ^{2} \simeq 17.2 $ and $χ^{2} \simeq 13.9$ (for all the 38 points in DAMPE electron/positron spectrum with 3 of them revised), respectively. These results are different from the previous analyses by neglecting the 1.4 TeV excess. At the same time, we do a similar global fitting on the newly released CALET lepton data, which could also be interpreted by such configurations. Moreover, we present a $U(1)_D$ dark matter model with Breit-Wigner mechanism, which can provide the proper dark matter annihilation cross section and escape the CMB constraint. Furthermore, we suggest a few ways to test our proposal.

hep-ph↗

arXiv2019

The least constrained supersymmetry with R-parity violation

The strong constraints on the R-parity conserving supersymmetry (SUSY) from the LHC searches motivate us to consider the new models in which the low-scale SUSY is still allowed. We propose a kind of R-parity violating SUSY scenarios with a non-zero $U^c_2 D^c_2 D^c_3$ operator. Three relevant LHC searches are recasted to test the status of this scenario in terms of four simplified models, with either light stop-Bino, stop-Higgsino, sbottom-Bino or sbottom-Higgsino. Some difficult scenarios for the LHC SUSY searches in these simplified models are identified. By extrapolate the current LHC searches to the future 14 TeV LHC with integrated luminosity of 300 fb$^{-1}$, most of the difficult scenarios can be probed, except the sbottom-Bino simplified one. An improved search, which utilises the multiple b-jets as well as its kinematic features, is expected to probe the signature of this case.

hep-ph↗

arXiv2019

Bayesian analysis of the hardening in AMS-02 nuclei spectra

Based on the precise nuclei data released by AMS-02, we study the spectra hardening of both the primary (proton, helium, carbon, oxygen, and the primary component of nitrogen) and the secondary (anti-proton, lithium, beryllium, boron and the secondary component of nitrogen) cosmic ray (CR) nuclei. With the diffusion-reacceleration model, we consider two schemes to reproduce the hardening in the spectra: (i) A high-rigidity break in primary source injection; (ii) A high-rigidity break in diffusion coefficient. The global fitting results show that both schemes could reproduce the spectra hardening in current status. More precise multi-TV data (especially the data of secondary CR species) is needed if one wants to distinguish these two schemes. In our global fitting, each of the nuclei species is allocated an independent solar modulation potential and a re-scale factor (which accounts for the isotopic abundance for primary nuclei species and uncertainties of production cross section or inhomogeneity of CR sources and propagation for secondary nuclei species). The fitting values of these two parameter classes show us some hints on some new directions in CR physics. All the fitted re-scale factors of primary nuclei species have values that systematically smaller than 1.0, while that of secondary nuclei species are systematically larger than 1.0. Moreover, both the re-scale factor and solar modulation potential of beryllium have values which are obviously different from other species. This might indicate that beryllium has the specificity not only on its propagation in the heliosphere, but also on its production cross section. All these new results should be seriously studied in the future.

astro-ph.HE↗

arXiv2019

The PeV-Scale Split Supersymmetry from Higgs Mass and Electroweak Vacuum Stability

The null results of the LHC searches have put strong bounds on new physics scenario such as supersymmetry (SUSY). With the latest values of top quark mass and strong coupling, we study the upper bounds on the sfermion masses in Split-SUSY from the observed Higgs boson mass and electroweak (EW) vacuum stability. To be consistent with the observed Higgs mass, we find that the largest value of supersymmetry breaking scales $M_{S}$ for $\tanβ=2$ and $\tanβ=4$ are $\mathcal{O} (10^{3}\, {\rm TeV})$ and $\mathcal{O} (10^{1.5}\, {\rm TeV})$ respectively, thus putting an upper bound on the sfermion masses around $10^{3}\, {\rm TeV}$. In addition, the Higgs quartic coupling becomes negative at much lower scale than the Standard Model (SM), and we extract the upper bound of $\mathcal{O}(10^{4}\, {\rm TeV})$ on the sfermion masses from EW vacuum stability. Therefore, we obtain the PeV-Scale Split-SUSY. The key point is the extra contributions to the Renormalization Group Equation (RGE) running from the couplings among Higgs boson, Higgsinos, and gauginos. We briefly comment on the lifetime of gluinos in our study and compare it with current LHC observations. Additionally, we comment on the prospects of discovery of prompt gluinos in a 100 TeV proton-propton collider.

hep-ph↗

arXiv2018

Search for the vectorlike leptons in the U(1)$_X$ model inspired by the $B$-meson decay anomalies

We consider the U(1)$_X$ model, which can induce the flavor violating couplings through vectorlike fermions and address the observed rare $B$-meson decay anomalies. To be consistent with all the other observations, both the associated gauge boson mass and the vectorlike lepton mass are bounded from above. We argue that the search for new vectorlike leptons is promising and provides a complement to the $Z'$ search. A detailed collider analysis shows that the model with the vectorlike lepton mass up to 1000 GeV could be tested at the future LHC.

hep-ph↗