arXiv subjects

Yi Liao

Publications and source records attributed to Yi Liao.

At least 109 records · Page 6Linked to original sources

arXiv2016

Renormalization Group Evolution of Dimension-seven Baryon- and Lepton-number-violating Operators

We study dimension-seven operators in standard model effective field theory. These operators are classified into two sets, one violating lepton number but preserving baryon number ($ΔL=\pm 2$, $ΔB=0$) and the other violating both but preserving their sum ($-ΔL=ΔB=\pm 1$). It has been found in the previous literature that there are respectively 13 and 7 such independent operators. We show that one operator is redundant in each set so that the complete list contains only 12 and 6 operators respectively. We accomplish this by using standard model equations of motion and various Fierz identities. We calculate the one-loop anomalous dimension matrix for the 6 operators in the second set, and illustrate its possible phenomenological implications by working out renormalization group running of the Wilson coefficients that could contribute to the type of proton decays with $-ΔL=ΔB=\pm 1$, such as $p\toνπ^+$.

hep-ph↗

arXiv2016

A mathematical form of force-free magnetosphere equation around Kerr black holes and its application to Meissner effect

Based on the Lagrangian of the steady axisymmetric force-free magnetosphere (FFM) equation around Kerr black holes(KBHs), we find that the FFM equation can be rewritten in a new form as $f_{,rr} / (1-μ^{2}) + f_{,μμ} / Δ+ K(f(r,μ),r,μ) = 0$, where $μ= -\cosθ$. By coordinate transformation, the form of the above equation can be given by $s_{,yy} + s_{,zz} + D(s(y,z),y,z) = 0$. Based on the form, we prove finally that the Meissner effect is not possessed by a KBH-FFM with the condition where $dω/d A_ϕ \leqslant 0$ and $H_ϕ(dH_ϕ/dA_ϕ) \geqslant 0$, here $A_ϕ$ is the $ϕ$ component of the vector potential $\vec{A}$, $ω$ is the angular velocity of magnetic fields and ${H_ϕ}$ corresponds to twice the poloidal electric current.

gr-qc↗

arXiv2016

Interpretation of 750 GeV Diphoton Excess at LHC in Singlet Extension of Color-octet Neutrino Mass Model

We propose that the possible 750 GeV diphoton excess can be explained in the color-octet neutrino mass model extended with a scalar singlet $Φ$. The model generally contains $N_s$ species of color-octet, electroweak doublet scalars $S$ and $N_f$ species of color-octet, electroweak triplet $χ$ or singlet $ρ$ fermions. While both scalars and fermions contribute to the production of $Φ$ through gluon fusion, only the charged members induce the diphoton decay of $Φ$. The diphoton rate can be significantly enhanced due to interference between the scalar and fermion loops. We show that the diphoton cross section can be from 3 to 10 fb for O(TeV) color-octet particles while evading all current LHC limits.

hep-ph↗

arXiv2016

Radiative Neutrino Mass with $Z_3$ Dark matter: From Relic Density to LHC Signatures

In this work we give a comprehensive analysis on the phenomenology of a specific $\mathbb{Z}_3$ dark matter (DM) model in which neutrino mass is induced at two loops by interactions with a DM particle that can be a complex scalar or a Dirac fermion. Both the DM properties in relic density and direct detection and the LHC signatures are examined in great detail, and indirect detection for gamma-ray excess from the Galactic Center is also discussed briefly. On the DM side, both semi-annihilation and co-annihilation processes play a crucial role in alleviating the tension of parameter space between relic density and direct detection. On the collider side, new decay channels resulting from $\mathbb{Z}_3$ particles lead to distinct signals at LHC. Currently the trilepton signal is expected to give the most stringent bound for both scalar and fermion DM candidates, and the signatures of fermion DM are very similar to those of electroweakinos in simplified supersymmetric models.

hep-ph↗

arXiv2015

A theoretical investigation on the transport properties of armchair biphenylene nanoribbons

Armchair biphenylene nanoribbons are investigated by using density functional theory. The nanoribbon that contains one biphenylene subunit in a unit cell is a semiconductor with a direct band gap larger than 1 eV, while that containing four biphenylene subunits is a metal. The semiconducting nanoribbon has high electron mobility of 57174 cm2V-1s-1, superior to armchair graphene nanoribbons. Negative differential resistance behavior is observed in two electronic devices composed of the semiconducting and metallic nanoribbons. The on/off ratios are in the order of 10^3. All these indicate that armchair biphenylene nanoribbons are potential candidates for ultra-small logic devices.

cond-mat.mes-hall↗

arXiv2015

LHC Phenomenology of the Type II Seesaw Mechanism: Observability of Neutral Scalars in the Nondegenerate Case

This is a sequel to our previous work on LHC phenomenology of the type II seesaw model in the nondegenerate case. In this work, we further study the pair and associated production of the neutral scalars H^0/A^0. We restrict ourselves to the so-called negative scenario characterized by the mass order M_{H^{\pm\pm}}>M_{H^\pm}>M_{H^0/A^0}, in which the H^0/A^0 production receives significant enhancement from cascade decays of the charged scalars H^{\pm\pm},~H^\pm. We consider three important signal channels---b\bar{b}γγ, b\bar{b}τ^+τ^-, $b\bar{b}\ell^+\ell^-\cancel{E}_T$---and perform detailed simulations. We find that at the 14 TeV LHC with an integrated luminosity of 3000/fb, a 5σmass reach of 151, 150, and 180 GeV, respectively, is possible in the three channels from the pure Drell-Yan H^0A^0 production, while the cascade-decay-enhanced H^0/A^0 production can push the mass limit further to 164, 177, and 200 GeV. The neutral scalars in the negative scenario are thus accessible at LHC run II.

hep-ph↗

arXiv2015

Abstractive Multi-Document Summarization via Phrase Selection and Merging

We propose an abstraction-based multi-document summarization framework that can construct new sentences by exploring more fine-grained syntactic units than sentences, namely, noun/verb phrases. Different from existing abstraction-based approaches, our method first constructs a pool of concepts and facts represented by phrases from the input documents. Then new sentences are generated by selecting and merging informative phrases to maximize the salience of phrases and meanwhile satisfy the sentence construction constraints. We employ integer linear optimization for conducting phrase selection and merging simultaneously in order to achieve the global optimal solution for a summary. Experimental results on the benchmark data set TAC 2011 show that our framework outperforms the state-of-the-art models under automated pyramid evaluation metric, and achieves reasonably well results on manual linguistic quality evaluation.

cs.CL↗

arXiv2015

LHC Phenomenology of Type II Seesaw: Nondegenerate Case

In this paper, we thoroughly investigate the LHC phenomenology of the type II seesaw mechanism for neutrino masses in the nondegenerate case where the triplet scalars of various charge ($H^{\pm\pm}, H^\pm, H^0, A^0$) have different masses. Compared with the degenerate case, the cascade decays of scalars lead to many new, interesting signal channels. In the positive scenario where $M_{H^{\pm\pm}} M_{H^\pm}>M_{H^0/A^0}$, the detection of $H^{\pm\pm}$ is more challenging, when the cascade decay $H^{\pm\pm}\to H^{\pm}W^{\pm*}$ is dominant. The most important channel is the associated $H^{\pm}H^0/A^0$ production in the final state $\ell^\pm\cancel{E}_Tb\bar{b}b\bar{b}$, which requires a luminosity of 109/fb for a $5σ$ discovery, while the final state $\ell^\pm\cancel{E}_Tb\bar{b}τ^+τ^-$ is less promising. Moreover, the associated $H^0A^0$ production can give same signals as the standard model Higgs pair production. With a much larger cross section, the $H^0A^0$ production in the final state $b\bar{b}τ^+τ^-$ could reach $3σ$ significance at 14 TeV LHC with a luminosity of 300/fb. In summary, with an integrated luminosity of order 500/fb, the triplet scalars can be fully reconstructed at 14 TeV LHC in the negative scenario.

hep-ph↗

arXiv2015

Reader-Aware Multi-Document Summarization via Sparse Coding

We propose a new MDS paradigm called reader-aware multi-document summarization (RA-MDS). Specifically, a set of reader comments associated with the news reports are also collected. The generated summaries from the reports for the event should be salient according to not only the reports but also the reader comments. To tackle this RA-MDS problem, we propose a sparse-coding-based method that is able to calculate the salience of the text units by jointly considering news reports and reader comments. Another reader-aware characteristic of our framework is to improve linguistic quality via entity rewriting. The rewriting consideration is jointly assessed together with other summarization requirements under a unified optimization model. To support the generation of compressive summaries via optimization, we explore a finer syntactic unit, namely, noun/verb phrase. In this work, we also generate a data set for conducting RA-MDS. Extensive experiments on this data set and some classical data sets demonstrate the effectiveness of our proposed approach.

cs.CL↗

arXiv2015

A theoretical prediction on huge hole and electron mobilities of 6,6,18-graphdiyne nanoribbons

Two-dimensional 6,6,18-graphdiyne and the corresponding one-dimensional nanoribbons are investigated using crystal orbital method. Based on HSE06 functional, the one-dimensional confinement increases the band gaps. With band gaps larger than 0.4 eV, thirty-three 6,6,18-graphdiyne nanoribbons have larger majority carrier mobilities at room temperature than the highest value of armchair graphene nanoribbons. Unlike γ-graphdiyne, 6,6,18-graphdiyne nanoribbons have both huge hole and electron mobilities, depending on whether they are armchair or zigzag type. The huge mobilities are explained by crystal orbital analysis. The superior capabilities of 6,6,18-graphdiyne nanoribbons make them possible candidates for high speed electronic devices in complementary circuits.

cond-mat.mtrl-sci↗

arXiv2014

Theoretical investigation on armchair graphene nanoribbons with oxygen-terminated edges

Armchair graphene nanoribbons with different proportions of edge oxygen atoms are investigated by using crystal orbital method based on density functional theory. All the nanoribbons are energetically favorable, although buckled edges are present. Isolated edge oxygen atoms cause semiconductor-metal transition via introducing edge states, while adjacent edge oxygen atoms not. For the graphene nanoribbons with all oxygen atoms on the edges, both band gap and carrier mobility alternate with respect to the ribbon width. The carrier mobilities are as 18%-65% large as those of the graphene nanoribbons with hydrogen-terminated edges. These values are as large as 103 cm2V-1s-1, which are still quite high for electronic devices. Crystal orbital analysis gives pictorial explanations to the phenomenon.

cond-mat.mtrl-sci↗

arXiv2014

Theoretical investigation on electronic properties and carrier mobilities of armchair graphyne nanoribbons

Seven types of armchair graphyne nanoribbons are investigated with HSE06 functional. The quantum confinements in the graphyne nanoribbons open or increase the band gaps of the corresponding two-dimensional graphynes, which is crucial to high on/off ratio in electronic device operation. The major carrier mobilities of the graphyne nanoribbons with high percentage of sp hybridized carbon atoms are very large. The sparse linking pattern results in small number of frontier crystal orbitals and small deformation potential constants, which are responsible for the large carrier mobilities. Some graphyne nanoribbons have band gaps larger than 0.4 eV. Meanwhile, they have both high hole and electron mobilities. These benefit current complementary circuit with low power dissipation. Especially, the hole and electron mobilities of 14,14,18-graphyne nanoribbons are more than an order larger than those of the armchair graphene nanoribbons, indicating that they have potential applications in high speed electronic devices.

cond-mat.mtrl-sci↗

arXiv2014

Phenomenology in Minimal Cascade Seesaw for Neutrino Mass

We make a comprehensive analysis on the phenomenology in the minimal version of cascade seesaw for tiny neutrino mass. The seesaw induces at tree level a neutrino mass operator at dimension nine, by introducing a quadruple scalar $Φ$ of hypercharge unity and a quintuple fermion $Σ$ of hypercharge zero. We work in a framework that handles the complicated Yukawa couplings in a nice way without losing generality. All mixing matrices are essentially expressed in terms of the vacuum expectation value of the quadruple scalar v_Φ, a free complex parameter, and known neutrino parameters. We show that the low-energy lepton flavor violating transitions of the charged leptons set strong constraints on the free parameters. The constraints have a significant impact on collider physics, and are incorporated in our signal analysis at the LHC. We investigate the signatures of new particles by surveying all potentially important channels. We find that the 4j2\ell^\pm signal is most important for the detection of the scalars and the 2\ell^{\pm}2\ell^{\mp}2j, 3\ell^{\pm}\ell^{\mp}2j and 3\ell^{\pm}2\ell^{\mp}+\cancel{E_T} signals are quite promising for the fermions.

hep-ph↗

arXiv2013

Comprehensive Constraints on a Spin-3/2 Singlet Particle as a Dark Matter Candidate

We consider the proposal that dark matter (DM) is composed of a spin-3/2 particle that is a singlet of the standard model (SM). Its leading effective interactions with ordinary matter involve a pair of their fields and a pair of SM fermions, in the form of products of chiral currents. We make a comprehensive analysis on possible phenomenological effects of the interactions in various experiments and observations. These include collider searches for monojet plus missing transverse energy events, direct detections of DM scattering off nuclei, possible impacts on the gamma rays and antiproton-to-proton flux ratio in cosmic rays, and the observed relic density. The current data already set strong constraints on the effective interactions in a complementary manner. The constraint from collider searches is most effective at a relatively low mass of DM, and the antiproton-to-proton flux ratio offers the best bound for a heavy DM, while the spin-independent direct detection is the best in between. For DM mass of order 10 GeV to 1 TeV, the effective interaction scale is constrained to be typically above a few tens TeV.

hep-ph↗

arXiv2013

Gauge Independence of Magnetic Moment and Vanishing Charge of Dirac Neutrinos: an Exact One-loop Demonstration

The magnetic moment and vanishing charge of a Dirac neutrino are physically observable quantities and must not depend on the choice of gauge in a consistent quantum field theory. We verify this statement explicitly at the one loop level in both R_xi and unitary gauges of the minimally extended standard model. We accomplish this by manipulating directly the integrands of loop integrals and employing simple algebraic identities and integral relations. Our result generally applies for any masses of the relevant particles and unitary neutrino mixing.

hep-ph↗

arXiv2012

The Superluminal Neutrinos from Deformed Lorentz Invariance

We study two superluminal neutrino scenarios where δv\equiv (v-c)/c is a constant. To be consistent with the OPERA, Borexino, and ICARUS experiments and with the SN1987a observations, we assume that δv_ν on the Earth is about three order larger than that on the interstellar scale. To explain the theoretical challenges from the Bremsstrahlung effects and pion decays, we consider the deformed Lorentz invariance, and show that the superluminal neutrino dispersion relations can be realized properly while the modifications to the dispersion relations of the other Standard Model particles can be negligible. In addition, we propose the deformed energy and momentum conservation laws for a generic physical process. In Scenario I the momentum conservation law is preserved while the energy conservation law is deformed. In Scenario II the energy conservation law is preserved while the momentum conservation law is deformed. We present the energy and momentum conservation laws in terms of neutrino momentum in Scenario I and in terms of neutrino energy in Scenario II. In such formats, the energy and momentum conservation laws are exactly the same as those in the traditional quantum field theory with Lorentz symmetry. Thus, all the above theoretical challenges can be automatically solved. We show explicitly that the Bremsstrahlung processes are forbidden and there is no problem for pion decays.

hep-ph↗

arXiv2012

Multi-photon Decays of the Higgs Boson in Standard Model: Leading Terms from Heisenberg-Euler Effective Lagrangian

We calculate the multi-photon decay widths of the Higgs boson from an effective Lagrangian for a system of electromagnetic and Higgs fields. We utilize a low-energy theorem to connect the above Lagrangian to the Heisenberg-Euler effective Lagrangian induced by charged particles that gain mass from interactions with the Higgs boson. In the standard model only the W^\pm gauge bosons and the top quark are relevant, and we compute their contributions to the effective couplings and the multi-photon decay widths of the Higgs boson.

hep-ph↗

arXiv2012

Generalized Fierz Identities and Applications to Spin-3/2 Particles

We study the most general Fierz identities for a pair of non-contracted Dirac matrices both in the standard basis and for chiral spinors. These identities are useful in building independent effective operators of fermions that involve derivatives or sextuple and more fields. We apply them to construct independent effective four-fermion interactions that contain one to three spin-3/2 chiral fields. These operators could be relevant to physics of higher-spin baryons and phenomenology of a neutral, massive spin-3/2 particle as a dark matter candidate.

hep-ph↗