arXiv subjects

Pei-Hong Gu

Publications and source records attributed to Pei-Hong Gu.

At least 19 recordsLinked to original sources

arXiv2026

Post-sphaleron conversion between baryon and lepton numbers

The conversion between baryon and lepton numbers has a significant impact on the mechanisms for dynamically generating the matter-antimatter asymmetry in the present universe. Under the traditional wisdom, such conversion originates from the so-called electroweak sphaleron processes. In this work we find that in association with a proper scalar and the other TeV new physics, the baryon-lepton conversion can still keep efficient after the electroweak sphalerons are no longer active. Moreover this scenario can provide a solution to the puzzle of neutron lifetime and predict some decay modes of multi-nucleons to multi-leptons.

hep-ph↗

arXiv2026

A new approach to dark photon

Over the past few decades, the hypothetically dark photon has been extensively studied from both phenomenological and experimental perspectives. It should be noted that the local symmetry for dark photon does not gauge the standard model Higgs scalar and chiral fermions. In this paper, we show that an artificially introduced $U(1)_X$ gauge group for dark photon and the standard model $U(1)_Y$ gauge group for hypercharge can be simultaneously born from two $U(1)_1\times U(1)_2$ gauge groups under which the standard model scalar and fermions carry the same $U(1)_1$ and $U(1)_2$ charges without causing any gauge anomalies. We further introduce a spontaneously broken mirror symmetry between the $U(1)_1$ and $U(1)_2$ gauge groups so that the $U(1)_1$ and $U(1)_2$ gauge couplings can acquire a small difference at one-loop level and hence the $U_X \times U_Y$ kinetic mixing can be highly suppressed in a natural way.

hep-ph↗

arXiv2025

New Physics Search at the CEPC: a General Perspective

The Circular Electron-Positron Collider (CEPC), a proposed next-generation Higgs factory, provides new opportunities to explore physics beyond the Standard Model (SM). With its clean electron-positron collision environment and the ability to collect large samples of Higgs, W, and Z bosons, the CEPC enables precision measurements and searches for new physics. This white paper outlines the CEPC's discovery potential, including studies of exotic decays of the Higgs, Z, and top quarks, dark matter and dark sector phenomena, long-lived particles, supersymmetry, and neutrino-related signatures. Advanced detector technologies and reconstruction techniques, such as one-to-one correspondence reconstruction and jet origin identification, significantly improve sensitivity to rare and weakly interacting processes. The CEPC is particularly well suited to probe the electroweak phase transition and test models of electroweak baryogenesis and dark sector interactions. In addition, global fit analyses highlight the CEPC's complementary role in constraining a wide range of new physics scenarios. These features position the CEPC as a powerful tool for exploring the next frontier in fundamental particle physics in the post-Higgs discovery era.

hep-ex↗

arXiv2023

Ultralight Dirac neutrinos from nearly degenerate Higgs doublets

Two Higgs doublets respect a mirror symmetry with spontaneous violation so that their vacuum expectation values can realize a small difference. Under this symmetry, three newly introduced right-handed neutrinos rather than the standard model fermions perform an odd transformation. Accordingly the neutrino masses and the charged fermion masses respectively are proportional to the difference and sum of the vacuum expectation values of two Higgs doublets. From a phenomenological perspective, such nearly degenerate Higgs doublets with large cancellation are equivalent to a Dirac seesaw mechanism with high suppression.

hep-ph↗

arXiv2023

Solving the strong CP problem by a $\barθ$-characterized mirror symmetry

In the standard model QCD Lagrangian, a term of CP violating gluon density is theoretically expected to have a physical coefficient $\barθ$ of the order of unity. However, the upper bound on the electric dipole moment of neutron enforces the value of $\barθ$ to be extremely small. Such a huge gap between theoretical expectation and experimental result is commonly known as the strong CP problem. To solve this puzzle in an appealing context of two Higgs doublets, we propose an economical $\barθ$-characterized mirror symmetry between two Higgs singlets with respective discrete symmetries. In our scenario, the parameter $\barθ$ can completely disappear from the full Lagrangian after the standard model fermions take a proper phase rotation as well as the Higgs doublets and singlets. Moreover, all of new physics for solving the strong CP problem can be allowed near the TeV scale.

hep-ph↗

arXiv2023

Axion from pseudo Goldstone seesaw without Peccei-Quinn symmetry

It is firmly believed that the axion for solving the strong CP problem must come from the spontaneous breaking of an anomalous Peccei-Quinn global symmetry. Here we show a new possibility that the axion can be induced by a pseudo Goldstone seesaw mechanism although the Peccei-Quinn symmetry is exactly forbidden. Specifically, after the spontaneous breaking of appropriate gauge and discrete symmetries, a heavy pseudo Goldstone coupling to colored fermions is allowed to have a tiny mass mixing with an ultralight pseudo Goldstone. In our scenario, no symmetry breaking is required to happen above the TeV scale. This means rich collider phenomena to explore the origin of axion.

hep-ph↗

arXiv2023

Heavy axions from twin dark sectors with $\barθ$-characterized mirror symmetry

The QCD Lagrangian contains a CP violating gluon density term with a physical coefficient $\barθ$. The upper bound on the electric dipole moment of neutron implies that the value of $\barθ$ should be extremely small rather than the theoretically expected order of unity. The tiny $\barθ$ is commonly known as the strong CP problem. In order to solve this puzzle, we construct a $\barθ$-characterized mirror symmetry between a pair of twin dark sectors with respective discrete symmetries. By taking a proper phase rotation of dark fields, we can perfectly remove the parameter $\barθ$ from the full Lagrangian. In our scenario, the discrete symmetry breaking, which are responsible for the mass generation of dark colored fermions and dark matter fermions, can be allowed near the TeV scale. This means different phenomena from the popular axion models with high scale Peccei-Quinn global symmetry breaking.

hep-ph↗

arXiv2022

$U(1)_{Y'}$ universal seesaw

We extend the $SU(3)_c \times SU(2)_L \times U(1)_Y$ standard model by a $U(1)_{Y'}$ gauge symmetry. Three right-handed neutrinos are introduced to cancel the gauge anomaly. One Higgs singlet is responsible for spontaneously breaking the $U(1)_{Y'}$ symmetry while the standard model Higgs doublet does not carry any $U(1)_{Y'}$ charges. The down-type quarks, up-type quarks, charged leptons and neutral neutrinos obtain their Dirac masses through four types of dimension-5 operators constructed by the fermion doublets and singlets with the Higgs doublet and singlet. This effective theory is realized in three renormalizable contexts with heavy fermion singlets, scalar doublets and fermion doublets. The heavy fermion singlets and doublets for generating the neutrino masses also accommodate a successful Dirac leptogenesis to explain the baryon asymmetry in the universe.

hep-ph↗

arXiv2022

Undemocratic Dirac seesaw

The standard model left-handed neutrinos and several right-handed neutrinos can obtain a tiny Dirac mass matrix through their mixings with relatively heavy Dirac fermions. In this Dirac seesaw scenario, the mixings involving the left-handed neutrinos can be allowed much larger than those involving the right-handed neutrinos. This undemocratic parameter choice is attractive to phenomenology. We show that the small mixings between the heavy Dirac fermions and the right-handed neutrinos can have a common origin with the observed baryon asymmetry in the universe. We also connect the introduction of right-handed neutrinos to the existence and stability of dark matter by a new $U(1)$ gauge symmetry for dark photon or baryon-minus-lepton number. We then specify how to embed our scenario into a left-right symmetric theory or a grand unification theory.

hep-ph↗

arXiv2021

Efficient approach to low scale Peccei-Quinn symmetry breaking without domain wall problem

We propose an efficient mechanism to realize an invisible axion from a low scale Peccei-Quinn symmetry breaking. Our basic model only contains a gauge boson, an up-type vector-like quark, two Higgs doublets and two Higgs singlets besides the standard model fermions and gauge bosons. The physical Peccei-Quinn global symmetry is a result of two independent global symmetries connected by the new gauge symmetry. Anyone of these two global symmetries only acts on either the right-handed top quark or the left-handed new quark so that it can avoid the domain wall problem. Thanks to the electroweak and new gauge interactions, the Higgs doublet for the top quark mass generation and the Higgs singlet for the new quark mass generation can only contribute a tiny fraction in the axion. The axion decay constant can be largely enhanced by a factor composed of the vacuum expectation values of the four Higgs scalars.

hep-ph↗

arXiv2021

Peccei-Quinn symmetry with residual symmetries

So far the null results from axion searches have enforced a huge hierarchy between the Peccei-Quinn and electroweak symmetry breaking scales. Then the inevitable Higgs portal poses a large fine tuning on the standard model Higgs scalar. Now we find if the Peccei-Quinn global symmetry has a set of residually discrete symmetries, these global and discrete symmetries can achieve a chain breaking at low scales such as the accessible TeV scale. This novel mechanism can accommodate some new phenomena including a sizable coupling of the standard model Higgs boson to the axion.

hep-ph↗

arXiv2021

Neutrinoless double beta decay without Majorana neutrinos

It is firmly believed that a signal of neutrinoless double beta decay can unquestionably confirm the Majorana nature of neutrinos. However we notice that a Majorana neutrino mass induced after some neutrinoless double beta decay processes can be accidentally cancelled by another Majorana neutrino mass induced before any neutrinoless double beta decay processes. This realistic cancellation can simultaneously allow an observable neutrinoless double beta decay and a vanishing Majorana neutrino mass. In consequence a future discovery of neutrinoless double beta decay cannot fully rule out the possibility of Dirac neutrinos.

hep-ph↗

arXiv2020

Split Higgs triplet

We find if a Higgs triplet with hypercharge has a special dimension-6 operator with the standard model Higgs doublet, i.e. a square of the trilinear triplet-doublet coupling, its scalar(pseudo-scalar) component can obtain a small quadratic term while its pseudo-scalar(scalar) and charged-scalar components can hold their masses heavy enough. Such split Higgs triplet can spontaneously develop a small vacuum expectation value to realize a Majorana neutrino mass generation without causing any high-dimensional lepton number violations including the well-known Weinberg dimension-5 operator. Alternatively it can mediate a non-standard neutrino self-interaction motivated by resolving the tension in Hubble constant measurements. This effective theory with rich observable phenomena can be induced by the Georgi-Machacek Higgs triplets at tree level or some dark matter fields at one-loop order.

hep-ph↗

arXiv2020

Weinberg dimension-5 operator by vector-like lepton doublets

It is well known that a Weinberg dimension-5 operator for small neutrino masses can be realized at tree level in three types of renormalizable models: (i) the type-I seesaw mediated by fermion singlets, (ii) the type-II seesaw mediated by Higgs triplets, (iii) the type-III seesaw mediated by fermion triplets. We here point out such operator can be also induced at tree level by vector-like lepton doublets in association with unusual fermion singlets, Higgs triplets or fermion triplets. If these unusual fermion singlets, Higgs triplets or fermion triplets are heavy enough, their decays can generate a lepton asymmetry to explain the cosmic baryon asymmetry, meanwhile, the vector-like lepton doublets can lead to a novel inverse or linear seesaw with rich observable phenomena. We further specify our scenario can be naturally embedded into a grand unification theory without the conventional type-I, type-II or type-III seesaw.

hep-ph↗

arXiv2019

Minimal inverse seesaw accompanied by Dirac fermionic dark matter

We present a minimal inverse seesaw mechanism by resorting to a $U(1)_{B-L}$ gauge symmetry. In order to cancel the gauge anomalies, we introduce seven neutral fermions among which four participate in the inverse seesaw to induce two nonzero neutrino mass eigenvalues, two forms a stable Dirac fermion to become a dark matter, while the last one keeps massless but decouples early. In this inverse seesaw, two neutral fermions are the usual right-handed neutrinos while the other two have a small Majorana mass term. An additional seesaw mechanism for generating these small Majorana masses also explains the cosmic baryon asymmetry in association with the sphaleron processes.

hep-ph↗

arXiv2019

Double type-II Dirac seesaw accompanied by Dirac fermionic dark matter

A TeV-scale Higgs doublet with a small mixing to the standard model Higgs doublet can have the sizable Yukawa couplings to several right-handed neutrinos and the standard model lepton doublets. This provides a testable Dirac neutrino mass generation. We further consider a seesaw mechanism involving a $U(1)_{B-L}^{}$ gauge symmetry, which predicts the existence of two right-handed neutrinos and a stable Dirac fermionic dark matter, to simultaneously explain the small mixing between the two Higgs doublets and the generation of the cosmic baryon asymmetry.

hep-ph↗

arXiv2019

Baryon asymmetry from left-right phase transition

We extend the standard model fermions by a mirror copy to realize a left-right symmetry. During a strongly first order phase transition of the spontaneous left-right symmetry breaking, the CP-violating reflections of the mirror fermions off the mirror Higgs bubbles can generate a mirror lepton asymmetry and an equal mirror baryon asymmetry. We then can obtain an ordinary baryon asymmetry through the mirror fermion decays where a dark matter scalar plays an essential role. Benefitted from a parity symmetry for solving the strong CP problem, the cosmic baryon asymmetry can be well described by the ordinary lepton mass matrices up to an overall factor. In this scenario, the Dirac CP phase in the Majorana neutrino mass matrix can provide a unique source for the required CP violation. Furthermore, the Higgs triplet for type-II seesaw as well as the first generation of mirror charged fermions can be allowed at the TeV scale.

hep-ph↗

arXiv2019

Parametrized leptogenesis from linear seesaw

We present a purely linear seesaw mechanism in a left-right symmetric framework and then realize a novel leptogenesis scenario for parametrizing the cosmic baryon asymmetty by the charged lepton masses and the light Majorana neutrino mass matrix up to an overall factor. Through the same Yukawa couplings, the lepton-number-conserving decays of the mirror charged leptons can generate three individual lepton asymmetries stored in the ordinary lepton flavors, while the lepton-number-violating processes for the Majorana neutrino mass generation can wash out part of these lepton asymmetries. The remnant lepton asymmetries then can be partially converted to a baryon asymmetry by the sphaleron processes. Our scenario prefers a normal hierarchical neutrino spectrum so that it could be verified by the future data from cosmological observations, neutrino oscillations and neutrinoless double beta decay.

hep-ph↗