arXiv subjects

Hong-Jian He

Publications and source records attributed to Hong-Jian He.

At least 37 records · Page 2Linked to original sources

arXiv2022

Massive Color-Kinematics Duality and Double-Copy for Kaluza-Klein Scattering Amplitudes

We study the scattering amplitudes of massive Kaluza-Klein (KK) states under toroidal compactification. We present a shifting method to quantitatively derive the scattering amplitudes of massive KK gauge bosons and KK gravitons from the corresponding massless amplitudes in the noncompactified higher dimensional theories. With these we construct the massive KK scattering amplitudes by extending the double-copy relations of massless scattering amplitudes within the field theory framework, including both the BCJ and CHY methods, and build up their connections to the massive KK KLT relations. We present the massive BCJ-type double-copy construction of the $N$-point KK gauge boson/graviton scattering amplitudes, and as the applications we derive explicitly the four-point KK scattering amplitudes as well as the five-point KK scattering amplitudes. We further study the nonrelativistic limit of these massive scattering amplitudes with the heavy external KK states and discuss the impact of the compactified extra dimensions on the low energy gravitational potential. Finally, we analyze the four-point and $N$-point mass spectral conditions and newly propose a novel group theory approach to prove that only the KK theories under toroidal compactification can satisfy these conditions for directly realizing massive double-copy in the field theory framework.

hep-th↗

arXiv2022

Probing Neutral Triple Gauge Couplings at the LHC and Future Hadron Colliders

We study probes of neutral triple gauge couplings (nTGCs) at the LHC and the proposed 100TeV $pp$ colliders, and compare their sensitivity reaches with those of the proposed $e^+ e^-$ colliders. The nTGCs provide a unique window to the new physics beyond the Standard Model (SM) because they can arise from SM effective field theory (SMEFT) operators that respect the full electroweak gauge group $SU(2)_L\otimes U(1)_Y$ of the SM only at the level of dimension-8 or higher. We derive the neutral triple gauge vertices (nTGVs) generated by these dimension-8 operators in the broken phase and map them onto a newly generalized form factor formulation, which takes into account only the residual U(1)$_{\rm{em}}$ gauge symmetry. Using this mapping, we derive new relations between the form factors that guarantee a truly consistent form factor formulation of the nTGVs and remove large unphysical energy-dependent terms. We then analyze the sensitivity reaches of the LHC and future 100TeV hadron colliders for probing the nTGCs via both the dimension-8 nTGC operators and the corresponding nTGC form factors in the reactions $ pp(q\bar{q})\to Zγ$ with $Z\to\ell^+\ell^-,ν\barν$. We compare their sensitivities with the existing LHC measurements of nTGCs and with those of the high-energy $e^+e^-$ colliders. In general, we find that the prospective LHC sensitivities are comparable to those of an $e^+ e^-$ collider with center-of-mass energy $\leq 1$TeV, whereas an $e^+ e^-$ collider with center-of-mass energy $(3 - 5)$TeV would have greater sensitivities, and a 100TeV $pp$ collider could provide the most sensitive probes of the nTGCs.

hep-ph↗

arXiv2022

Structure of Kaluza-Klein Graviton Scattering Amplitudes from Gravitational Equivalence Theorem and Double-Copy

We study the structure of scattering amplitudes of the Kaluza-Klein (KK) gravitons and of the gravitational KK Goldstone bosons in the compactified 5d General Relativity (GR). We analyze the geometric "Higgs" mechanism for mass-generation of KK gravitons under compactification with a general $R_ξ$ gauge-fixing, which is free from the vDVZ discontinuity. Then, we formulate the Gravitational Equivalence Theorem (GRET) to connect the longitudinal KK graviton amplitudes to the KK Goldstone amplitudes, which is a manifestation of the geometric Higgs mechanism at $S$-matrix level. We directly compute the tree-level KK Goldstone amplitudes which equal the longitudinal KK graviton amplitudes in the high energy limit. We further extend the double-copy method with color-kinematics duality to reconstruct the massive KK longitudinal graviton (Goldstone) amplitudes from the KK longitudinal gauge boson (Goldstone) amplitudes in the compactified 5d Yang-Mills (YM) theory under high energy expansion. From these, we reconstruct the GRET of the KK longitudinal graviton (Goldstone) amplitudes in the 5d GR from the KK longitudinal gauge boson (Goldstone) amplitudes in the 5d YM theory. Using either the GRET or the double-copy reconstruction, we provide a theoretical mechanism showing that the sum of all the energy-power terms [up to $O(E^{10})$] in the high-energy four longitudinal KK graviton amplitudes must cancel down to $O(E^2)$ as enforced by matching the energy-power dependence of the corresponding KK Goldstone amplitudes or by matching that of the double-copy amplitudes from the KK YM theory. With the double-copy approach, we establish a new correspondence between the two energy-cancellations: $E^4 \to E^0$ in the 5d KK YM theory and $E^{10} \to E^2$ in the 5d KK GR theory. We further analyze the structure of the residual terms in the GRET and uncover a new energy-cancellation mechanism therein.

hep-th↗

arXiv2022

Gravitational Equivalence Theorem and Double-Copy for Kaluza-Klein Graviton Scattering Amplitudes

We analyze the structure of scattering amplitudes of the Kaluza-Klein (KK) gravitons and of the KK gravitational Goldstone bosons in the compactified 5d General Relativity (GR). Using a general $R_ξ$ gauge-fixing, we study the geometric Higgs mechanism for the massive spin-2 KK gravitons. We newly propose and prove a Gravitational Equivalence Theorem (GRET) to connect the scattering amplitudes of longitudinal KK gravitons to that of the KK gravitational Goldstone bosons, which formulates the geometric gravitational Higgs mechanism at the scattering $S$-matrix level. We demonstrate that the GRET provides a general energy-cancellation mechanism guaranteeing the $N$-point longitudinal KK graviton scattering amplitudes to have their leading energy dependence cancelled down by a large power factor of $E^{2N}$ ($N \geq 4$) up to any loop order. We propose an extended double-copy approach to construct the massive KK graviton (Goldstone) amplitudes from the KK gauge boson (Goldstone) amplitudes. With these we establish a new correspondence between the two types of energy cancellations in the four-point longitudinal KK amplitudes at tree level: $E^4\to E^0$ in the KK gauge theory and $E^{10} \to E^2$ in the KK GR theory.

hep-th↗

arXiv2022

Scattering Amplitudes of Kaluza-Klein Strings and Extended Massive Double-Copy

We study the scattering amplitudes of massive Kaluza-Klein (KK) states of open and closed bosonic strings under toroidal compactification. We analyze the structure of vertex operators for the KK strings and derive an extended massive KLT-like relation which connects the $N$-point KK closed-string amplitude to the products of two KK open-string amplitudes at tree level. Taking the low energy field-theory limit of vanishing Regge slope, we derive double-copy construction formula of the $N$-point massive KK graviton amplitude from the sum of proper products of the corresponding KK gauge boson amplitudes. Then, using the string-based massive double-copy formula, we derive the exact tree-level four-point KK gauge boson amplitudes and KK graviton amplitudes, which fully agree with those given by the KK field-theory calculations. With these, we give an explicit prescription on constructing the exact four-point KK graviton amplitudes from the sum of proper products of the corresponding color-ordered KK gauge boson amplitudes. We further analyze the string-based double-copy construction of five-point and six-point scattering amplitudes of massive KK gauge bosons and KK gravitons.

hep-th↗

arXiv2022

GeV Scale Inelastic Dark Matter with Dark Photon Mediator via Direct Detection and Cosmological/Laboratory Constraints

We propose a new candidate of GeV scale inelastic dark matter (DM). Our construction has an anomaly-free $U(1)_X^{}$ gauge group with dark photon mediator, and can realize either scalar or fermionic inelastic DM. It is highly predictive and testable. We study the scattering rate of light inelastic DM with electrons in the XENON1T experiment and with nuclei in the XENON1T, CRESST-III, CDEX-1B and DarkSide-50 experiments. We resolve the recent XENON1T anomaly via electron recoil detection. Combining the XENON1T constraints from both electron recoils and nuclear recoils (including Migdal effect), we predict the inelastic DM mass $\lesssim 1.5$GeV. We further analyze the bounds by the DM relic abundance, the lifetime of the heavier DM component, and laboratory constraints, from which we identify the viable parameter space for the future probe. This provides an important benchmark for the theories and experimental tests of GeV scale inelastic DM.

hep-ph↗

arXiv2021

Structure of Chern-Simons Scattering Amplitudes from Topological Equivalence Theorem and Double-Copy

We study the mechanism of topological mass-generation for 3d Chern-Simons (CS) gauge theories, where the CS term can retain the gauge symmetry and make gauge boson topologically massive. Without CS term the 3d massless gauge boson has a single physical transverse polarization state, while adding the CS term converts it into a massive physical polarization state and conserves the total physical degrees of freedom. We newly formulate the mechanism of topological mass-generation at $S$-matrix level. For this, we propose and prove a new Topological Equivalence Theorem (TET) which connects the $N$-point scattering amplitude of the gauge boson's physical polarization states ($A^a_{\rm{P}}$) to that of the transverse polarization states ($A^a_{\rm{T}}$) under high energy expansion. We present a general 3d power counting method on the leading energy dependence of $N$-point scattering amplitudes in both topologically massive Yang-Mills (TMYM) and topologically massive gravity (TMG) theories. With these, we uncover a general energy cancellation mechanism for $N$-gauge boson scattering amplitudes which predicts the cancellation $E^4 \to E^{4-N}$ at tree level. Then, we compute the four-point amplitudes of $A^a_{\rm{P}}$'s and of $A^a_{\rm{T}}$'s, with which we explicitly demonstrate the TET and establish such energy cancellations. We further extend the double-copy approach and construct the four-point massive graviton amplitude of the TMG theory from the massive gauge boson amplitude of the TMYM theory. With these, we newly uncover striking large energy cancellations $E^{12}\to E^1$ in the four-graviton amplitude of the TMG, and establish its new correspondence to the leading energy cancellations $E^4 \to E^0$ in the four-gauge boson amplitude of the TMYM.

hep-th↗

arXiv2020

Probing New Physics in Dimension-8 Neutral Gauge Couplings at $e^+e^-$ Colliders

Neutral triple gauge couplings (nTGCs) are absent in the standard model effective theory up to dimension-6 operators, but could arise from dimension-8 effective operators. In this work, we study the pure gauge operators of dimension-8 that contribute to nTGCs and are independent of the dimension-8 operator involving the Higgs doublet. We show that the pure gauge operators generate both $ZγZ^*$ and $Zγγ^*$ vertices with rapid energy dependence $\propto E^5$, which can be probed sensitively via the reaction $e^+e^- \to Zγ$. We demonstrate that measuring the nTGCs via the reaction $e^+e^- \to Zγ$ followed by $Z \to q\bar{q}$ decays can probe the new physics scales of dimension-8 pure gauge operators up to the range $(1-5)$TeV at the CEPC, FCC-ee and ILC colliders with $\sqrt{s}=(0.25-1)$TeV, and up to the range $(10-16)$TeV at CLIC with $\sqrt{s}=(3-5)$TeV, assuming in each case an integrated luminosity of 5/ab. We compare these sensitivities with the corresponding probes of the dimension-8 nTGC operators involving Higgs doublets and the dimension-8 fermionic contact operators that contribute to the $e^+e^-Zγ$ vertex.

hep-ph↗

arXiv2020

Reconciling Hubble Constant Discrepancy from Holographic Dark Energy

Holographic dark energy (HDE) describes the vacuum energy in a cosmic IR region whose total energy saturates the limit of avoiding the collapse into a black hole. HDE predicts that the dark energy equation of the state transiting from greater than the $-1$ regime to less than $-1$, accelerating the Universe slower at the early stage and faster at the late stage. We propose the HDE as a new {\it physical} resolution to the Hubble constant discrepancy between the cosmic microwave background (CMB) and local measurements. With Planck CMB and galaxy baryon acoustic oscillation (BAO) data, we fit the HDE prediction of the Hubble constant as $H_0^{}\!=\, 71.54\pm1.78\,\mathrm{km\,s^{-1} Mpc^{-1}}$, consistent with local $H_0^{}$ measurements by LMC Cepheid Standards (R19) at $1.4σ$ level. Combining Planck+BAO+R19, we find the HDE parameter $c=0.51\pm0.02$ and $H_0^{}\! = 73.12\pm 1.14\,\mathrm{km \,s^{-1} Mpc^{-1}}$, which fits cosmological data at all redshifts. Future CMB and large-scale structure surveys will further test the holographic scenario.

astro-ph.CO↗

arXiv2020

EFT Approach of Inelastic Dark Matter for Xenon Electron Recoil Detection

Measuring dark matter (DM) signals via electron recoil provides an important means for direct detection of light DM particles. The recent XENON1T anomaly with electron recoil energy around $\,E_R^{}\!=\!(2-3)$keV can be naturally explained by DM inelastic scattering which injects energy to the recoiled electrons and gives a narrow peak structure in the recoil spectrum. We present an effective field theory (EFT) approach to exothermic inelastic DM signals for the Xenon electron recoil detection. For relatively heavy mediator, we fairly formulate the DM-lepton interactions by effective contact operators with two DM fields $(X,\,X')$ and two leptons. Using the XENON1T data, we fit the electron recoil spectrum and constrain the allowed scalar DM mass-splitting as $\,2.1\,\text{keV}\!<\!Δm\!<\!3.3\,\text{keV}$ (95%C.L.), with the best fit $\,Δm \!=\! 2.8$keV. We analyze the relic abundance produced by such effective DM-electron contact interaction. To provide both the DM relic abundance and the XENON1T excess, we derive new constraints on the DM mass and the UV cutoff scale of DM effective interactions. Finally, we study possible UV completions for the effective DM-lepton contact interactions.

hep-ph↗

arXiv2020

Resolving Hubble Tension by Self-Interacting Neutrinos with Dirac Seesaw

Self-interacting neutrinos that begin to free-stream at close to matter-radiation equality can reduce the physical size of photon sound horizon at last scattering surface. This mechanism can be the reason why standard $Λ$CDM cosmology sees a lower value of the Hubble constant than local measurements from distance ladder. We propose a new realization of self-interacting Dirac neutrinos (SID$ν$) with light-dark-photon mediator for a viable interaction mechanism. Our model is UV completed by a Dirac seesaw with anomaly-free dark $U(1)_X^{}$ gauge group which charges the right-handed neutrinos. This model naturally generates small masses for Dirac neutrinos and induces self-scattering of right-handed neutrinos. The scattering with left-handed neutrinos is suppressed by a chirality-flip mass insertion when the neutrino energy is much larger than its mass. The resultant neutrino self-scattering is not operative for $E_ν\gtrsim O(\text{keV})$, which avoids the cosmological and laboratory constraints. By evolving Boltzmann equations for left- and right-handed neutrino number densities, we show that about $2/3$ of the left-handed neutrinos are converted into right-handed neutrinos in a short epoch between the Big-Bang Nucleosynthesis and the recombination, and interact with each other efficiently afterwards. The resultant neutrino non-free-streaming is the crucial ingredient to shrink down the comoving sound horizon at drag epoch, which can reconcile the Hubble tension between early and late time measurements.

hep-ph↗

arXiv2020

Probing Flavor Structure of Cosmic Ray $e^\mp$ Spectrum and Implications for Dark Matter Indirect Searches

Measuring high energy cosmic ray electrons/positrons (CRE) provides important means for the dark matter (DM) indirect detection and for probing the nearby galactic sources. In this work, we perform a systematic analysis of the flavor structure of DM annihilations into charged leptons based on the cosmic ray CRE spectra measured by DAMPE, Fermi-LAT, AMS-02, and CALET experiments. We study the annihilations of possible TeV scale DM particles in a nearby subhalo, which is proposed to explain the possible peak-like structure of the DAMPE CRE data. We pay special attention to the possible non-resonant excess (besides the possible peak-like structure) and demonstrate that such non-resonant excess can mainly arise from the decay of muons produced by the DM annihilations in the subhalo. With these we study the flavor composition of the lepton final states from DM annihilations $χχ\to e^+e^-, μ^+μ^-, τ^+τ^-$ by fitting the CRE data. We demonstrate that decays of the final states $μ^+ μ^-$ and $τ^+ τ^-$ can provide the non-resonant excess, while the peak excess arises from the $e^+ e^-$ final state. We further analyze the constraints on the lepton flavor composition using the Fermi-LAT $γ$-ray measurements. We find that the flavor composition is consistent with the Fermi-LAT data at relatively low Galactic latitudes, while the fraction of the final state $τ^\pm$ is severely bounded.

astro-ph.HE↗

arXiv2020

Probing the Scale of New Physics in the $ZZγ$ Coupling at $e^+e^-$ Colliders

The $ZZγ$ triple neutral gauge couplings are absent in the Standard Model (SM) at the tree level. They receive no contributions from dimension-6 effective operators, but can arise from effective operators of dimension-8. We study the scale of new physics associated with such dimension-8 operators that can be probed by measuring the reaction $e^+e^-\to Zγ$, followed by $Z \to \ell\bar{\ell},ν\barν$ decays, at future $e^+e^-$ colliders including the ILC, CEPC, FCC-ee and CLIC. We demonstrate how angular distributions of the final state mono-photon and leptons can play a key role in suppressing SM backgrounds. We further show that using electron/positron beam polarizations can significantly improve the signal sensitivities. We find that the dimension-8 new physics scale can be probed up to the multi-TeV region at such lepton colliders.

hep-ph↗

arXiv2019

Probing Dynamics of Boson Stars by Fast Radio Bursts and Gravitational Wave Detection

Boson stars may consist of a new type of light singlet scalar particles with nontrivial self-interactions, and may compose a fraction of the dark matter in the Universe. In this work, we study the dynamics of boson stars with Liouville and logarithmic scalar self-interaction potentials as benchmarks. We perform a numerical analysis as well as a semi-analytic study on how the compactness and the total mass will deviate from that of the usual boson stars formed with a quartic repulsive self-interaction. We apply the recently suggested Swampland conjecture to examine whether boson stars with such benchmark potentials belong to the Landscape of a quantum gravity. Using the mass constraint on the macroscopic compact halo object (MACHO) and the cold dark matter (CDM) isocurvature mode constraint from the cosmic microwave background (CMB), we derive the allowed mass range of scalar particles which compose the boson star. We further analyze applications of the lensing of fast radio bursts (FRBs) and the gravitational wave (GW) detection to probe the presence of such boson stars and constrain the parameter space of their corresponding models. We discuss how the two types of boson star potentials can be discriminated by the FRB and GW measurements.

astro-ph.CO↗

arXiv2019

Precision Higgs Physics at CEPC

The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics. The Higgs boson will be the subject of extensive studies of the ongoing LHC program. At the same time, lepton collider based Higgs factories have been proposed as a possible next step beyond the LHC, with its main goal to precisely measure the properties of the Higgs boson and probe potential new physics associated with the Higgs boson. The Circular Electron Positron Collider~(CEPC) is one of such proposed Higgs factories. The CEPC is an $e^+e^-$ circular collider proposed by and to be hosted in China. Located in a tunnel of approximately 100~km in circumference, it will operate at a center-of-mass energy of 240~GeV as the Higgs factory. In this paper, we present the first estimates on the precision of the Higgs boson property measurements achievable at the CEPC and discuss implications of these measurements.

hep-ex↗

arXiv2019

TeV Scale Neutrino Mass Generation, Minimal Inelastic Dark Matter, and High Scale Leptogenesis

The seesaw and leptogenesis commonly depend on the masses of same particles, and thus are both realized at the same scale. In this work, we demonstrate a new possibility to realize a TeV-scale neutrino seesaw and a natural high-scale leptogenesis. We extend the standard model by two gauge-singlet scalars, a vector-like iso-doublet fermion and one iso-triplet Higgs scalar. Our model respects a softly broken lepton number and an exactly conserved $Z_2$ discrete symmetry. It can achieve three things altogether: (i) realizing a testable type-II seesaw at TeV scale with two nonzero neutrino mass-eigenvalues, (ii) providing a minimal inelastic dark matter from the new fermion doublets, and (iii) accommodating a thermal or nonthermal leptogenesis through the singlet scalar decays. We further analyze the current experimental constraints on our model and discuss the implications for the dark matter direct detections and the LHC searches.

hep-ph↗

arXiv2018

LHC Search of New Higgs Boson via Resonant Di-Higgs Production with Decays into 4W

Searching for new Higgs particle beyond the observed light Higgs boson h(125GeV) will unambiguously point to new physics beyond the standard model. We study the resonant production of a CP-even heavy Higgs state $H^0$ in the di-Higgs channel via, $gg\to H^0\to h^0h^0\to WW^*WW^*$, at the LHC Run-2 and the high luminosity LHC (HL-LHC). We analyze two types of the $4W$ decay modes, one with the same-sign di-leptons ($4W\to\ell^\pmν\ell^\pmν4q$) and the other with tri-leptons ($4W\to\ell^\pmν\ell^\mpν\ell^\pmν2q$). We perform a full simulation for the signals and backgrounds, and estimate the discovery potential of the heavy Higgs state at the LHC Run-2 and the HL-LHC, in the context of generical two-Higgs-doublet models (2HDM). We determine the viable parameter space of the 2HDM as allowed by the theoretical constraints and the current experimental limits. We systematically analyze the allowed parameter space of the 2HDM which can be effectively probed by the heavy Higgs searches of the LHC, and further compare this with the viable parameter region under the current theoretical and experimental bounds.

hep-ph↗

arXiv2018

Flavor Structure of the Cosmic-Ray Electron/Positron Excesses at DAMPE

The Dark Matter Particle Explorer (DAMPE) satellite detector announced its first result for measuring the cosmic-ray electron/positron (CRE) energy spectrum up to 4.6TeV, including a tentative peak-like event excess at (1.3-1.5)TeV. In this work, we uncover a significant hidden excess in the DAMPE CRE spectrum over the energy range (0.6-1.1)TeV, which has a non-peak-like structure. We propose a new mechanism to explain this excess by a set of 1.5TeV $μ^\pm$ events with subsequent decays into $e^\pm$ plus neutrinos. For explaining this new excess together with the peak excess around 1.4TeV, we demonstrate that the {\it flavor structure} of the original lepton final-state produced by dark matter (DM) annihilations (or other mechanism) should have a composition ratio $N_e : (N_μ+\frac{1}{6}N_τ) = 1 : y$, with $y \simeq 2.6-10.8$. For lepton portal DM models, this puts important constraint on the lepton-DM-mediator couplings $λ_e : (λ_μ^4 + \frac{1}{6}λ_τ^4)^{\frac{1}{4}} = 1 : y^{\frac{1}{4}}$ with a narrow range $y^{\frac{1}{4}} \simeq 1.3-1.8$.

astro-ph.HE↗