arXiv subjects

Zhaofeng Kang

Publications and source records attributed to Zhaofeng Kang.

At least 37 records · Page 2Linked to original sources

arXiv2019

Slightly Ultra-violet Freeze-in a Hidden Gluonic Sector

The dark glueball (DGB) from a hidden Yang-Mills sector is a simple non-WIMP dark matter candidate characterized by very few parameters. However, it suffers the over dense issue. To overcome it, in general the dark sector is required to be hierarchically cooler than the visible sector. To naturally generate the desired hierarchy, in this paper we introduce higher dimensional operators coupling the dark gauge field strength tensor to the standard model (SM) Higgs doublets or gauge field strength tensors. By tracking the different phases of the universe from the end of inflation, prethermalization, reheating to the radiation dominance era, we show that these operators can make the DGB be a viable dark matter candidate over a wide mass region, from the sub-GeV to multi-PeV or even beyond. At the same time, these operators open decay channels of DGB to the SM species, and partial of the parameter space could leave hints in the cosmic ray.

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arXiv2019

Scalar Quintuplet Minimal Dark Matter with Yukawa Interactions: Perturbative up to the Planck Scale

We confront the perturbativity problem in the real scalar quintuplet minimal dark matter model. In the original model, the quintuplet quartic self-coupling inevitably hits a Landau pole at a scale $\sim 10^{14}$ GeV, far below the Planck scale. In order to push up this Landau pole scale, we extend the model with a fermionic quintuplet and three fermionic singlets which couple to the scalar quintuplet via Yukawa interactions. Involving such Yukawa interactions at a scale $\sim 10^{10}$ GeV can not only keep all couplings perturbative up to the Planck scale, but can also explain the smallness of neutrino masses via the type-I seesaw mechanism. Furthermore, we identify the parameter regions favored by the condition that perturbativity and vacuum stability are both maintained up to the Planck scale.

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arXiv2018

Post-recombination Dark Matter for the 21-cm Signal

We have no certain knowledge of the early history of dark matter (DM). In this paper we propose a scenario where DM is produced post-recombination but prior to the cosmic dawn. It helps to relax the bounds on DM interactions, in particular with baryons, from the CMB. It may be of interest in some circumstances, for example, to understand the recent cosmic dawn 21-cm signal anomaly. We argue that the cosmic gas cooling mechanism via the minicharged DM-baryon scattering may be viable even if it takes up the total DM budget. We also investigate the possibility of a gluon-philic mediator of a few 10 keV, to find that the most reliable exclusion is from the neutron scattering.

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arXiv2018

Minimal Dark Matter in the Local $B-L$ Extension

The minimal gauge group extension to the standard model (SM) by the local $U(1)_{B-L}$ (MBLSM) is well known as the minimal model to understand neutrino mass origins via the seesaw mechanism, following the gauge principle. This "small" symmetry also has deep implication to another big thing, dark matter (DM) stability. We demonstrate it in the framework of minimal dark matter (MDM), which aims at addressing two basic questions on DM, stability and the nature of interactions. However, stability and perturbativity may only allow the fermionic quintuplet. The situation is very different in the MBLSM, which leaves the subgroup of $U(1)_{B-L}$, the matter parity $(-1)^{3(B-L)}$, unbroken; it is able to stabilize all of the weakly-interacting {MDM candidates } after assigning a proper $U(1)_{B-L}$ charge. For the candidates with nonzero hypercharge, the phenomenological challenge comes from realizing the inelastic DM scenario thus evading the very strict DM direct detention bounds. We present two approaches that can slightly split the CP-even and -odd parts of the neutral components: 1) using the dimension 5 operators, which works for the $U(1)_{B-L}$ spontaneously breaking at very high scale; 2) mixing with {other fields} having zero hypercharge, which instead works for a low $U(1)_{B-L}$ breaking scale.

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arXiv2017

On UltraViolet Freeze-in Dark Matter during Reheating

The absence of any confirmative signals from extensive DM searching motivates us to go beyond the conventional WIMPs scenario. The feebly interacting massive particles (FIMPs) paradigm provides a good alternative which, despite of its feebly interaction with the thermal particles, still could correctly produce relic abundance without conventional DM signals. The Infrared-FIMP based on the renormalizable operators is usually suffering the very tiny coupling drawback, which can be overcome in the UltraViolet-FIMP scenario based on high dimensional effective operators. However, it is sensitive to the history of the very early Universe. The previous works terminates this sensitivity at the reheating temperature $T_{RH}$. We, motivated by its UV-sensitivity, investigate the effects from the even earlier Universe, reheating era. We find that in the usual case with $T_{RH}\gg m_{\rm DM}$, the production rate during reheating is very small as long as the effective operators dimension $d \leq 8$. Besides, we consider the contribution from the mediator, which may be produced during reheating. Moreover, we study the situation when $T_{RH}$ is even lower than $m_{\rm DM}$ and DM can be directly produced during reheating if its mass does not exceed $T_{MAX}$.

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arXiv2017

Strong First Order EWPT and Strong Gravitational Waves in $Z_3$-symmetric Singlet Scalar Extension

The nature of electroweak (EW) phase transition (PT) is of great importance. It may give a clue to the origin of baryon asymmetry if EWPT is strong first order. Although it is second order within the standard model (SM), a great many extensions of the SM are capable of altering the nature. Thus, gravitational wave (GW), which is supposed to be relics of strong first order PT, is a good complementary probe to new physics beyond SM (BSM). We in this paper elaborate the patterns of strong first order EWPT in the next to simplest extension to the SM Higgs sector, by introducing a $Z_3$-symmetric singlet scalar. We find that, in the $Z_3$-symmetric limit, the tree level barrier could lead to strong first order EWPT either via three or two-step PT. Moreover, they could produce two sources of GW, despite of the undetectability from the first-step strong first order PT for the near future GW experiments. But the other source with significant supercooling which then gives rise to $α\sim{\cal O}(0.1)$ almost can be wholly covered by future space-based GW interferometers such as eLISA, DECIGO and BBO.

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arXiv2017

Bound States via Higgs Exchanging and Resonant Di-Higgs

The standard model (SM)-like Higgs boson $h$ has spin zero and light mass around weak scale, so it has the potential to mediate a new and relatively strong force for the particle $ϕ$ in the new physics (NP) sector; then $ϕ$ may form bound state $B_h$ via exchanging $h$. This phenomena may arise in a wide context, for instance composite Higgs, supersymmetry (SUSY) and radiative neutrino (or more widely in the models with a strong Higgs portal for triggering classical scale symmetry breaking or strong first-order phase transition). For illustration we focus on two typical examples, the stop/sbottom sector and an inert Higgs doublet. Furthermore, we point out that $B_h$ must give rise to a clear resonant di-Higgs signature, which recently has been extensively searched for at the large hadron collider (LHC). Moreover, Higgs radiative decay such as to di-photon probably will be significantly modified provided that $ϕ$ is charged or/and colored.

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arXiv2017

Asymmetric Dark Matter Bound State

We propose an interesting framework for asymmetric scalar dark matter (ADM), which has novel collider phenomenology in terms of an unstable ADM bound state (ADMonium) produced via Higgs portals. ADMonium is a natural consequence of the basic features of ADM: the (complex scalar) ADM is charged under a dark local $U(1)_d$ symmetry which is broken at a low scale and provides a light gauge boson $X$. The dark gauge coupling is strong and then ADM can annihilate away into $X$-pair effectively. Therefore, the ADM can form bound state due to its large self-interaction via $X$ mediation. To explore the collider signature of ADMonium, we propose that ADM has a two-Higgs doublet portal. The ADMonium can have a sizable mixing with the heavier Higgs boson, which admits a large cross section of ADMonium production associated with $b\bar b$. The resulting signature at the LHC depends on the decays of $X$. In this paper we consider a case of particular interest: $pp\ra b\bar b+ {\rm ADMonium}$ followed by ${\rm ADMonium}\ra 2X\ra 2e^+e^-$ where the electrons are identified as (un)converted photons. It may provide a competitive explanation to heavy di-photon resonance searches at the LHC.

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arXiv2017

Uncover Compressed Supersymmetry via Boosted Bosons from the Heavier Stop/Sbottom

A light stop around the weak scale is a hopeful messenger of natural supersymmetry (SUSY), but it has not shown up at the current stage of LHC. Such a situation raises the question of the fate of natural SUSY. Actually, a relatively light stop can easily be hidden in a compressed spectra such as mild mass degeneracy between stop and neutralino plus top quark. Searching for such a stop at the LHC is a challenge. On the other hand, in terms of the argument of natural SUSY, other members in the stop sector, including a heavier stop $\tilde{t}_2$ and lighter sbottom $\tilde{b}_1$ (both assumed to be left-handed-like), are also supposed to be relatively light and therefore searching for them would provide an alternative method to probe natural SUSY with a compressed spectrum. In this paper we consider quasi-natural SUSY which tolerates relatively heavy colored partners near the TeV scale, with a moderately large mass gap between the heavier members and the lightest stop. Then $W/Z/h$ as companions of $\tilde{t}_2$ and $\tilde{b}_1$ decaying into $\tilde{t}_1$ generically are well boosted, and they, along with other visible particles from $\tilde{t}_1$ decay, are a good probe to study compressed SUSY. We find that the resulting search strategy with boosted bosons can have better sensitivity than those utilizing multi-leptons.

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arXiv2017

Right-handed neutrino dark matter under the B-L gauge interaction

We study the right-handed neutrino (RHN) dark matter candidate in the minimal U(1)_{B-L} gauge extension of the standard model. The U(1)_{B-L} gauge symmetry offers three RHNs which can address the origin of the neutrino mass, the relic dark matter, and the matter-antimatter asymmetry of the universe. The lightest among the three is taken as the dark matter candidate, which is under the B-L gauge interaction. We investigate various scenarios for this dark matter candidate with the correct relic density by means of the freeze-out or freeze-in mechanism. A viable RHN dark matter mass lies in a wide range including keV to TeV scale. We emphasize the sub-electroweak scale light B-L gauge boson case, and identify the parameter region motivated from the dark matter physics, which can be tested with the planned experiments including the CERN SHiP experiment.

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arXiv2017

Missing particle associated with two bottom quarks at the LHC: Mono-$b$ versus 2$b$ with razor variables

The extended Higgs sector, such as by a second Higgs doublet of type-II, provides portals to dark sector which contains missing particles at the LHC, e.g., dark matter (DM) particles. In this paper, working in the simplified model and taking into consideration the wide decay width effect of the mediator, we analyze the characteristic signatures of mono-$b$+MET and 2$b$+MET at the LHC. The latter signature was believed to be ineffective, while we found that, with the aid of razor shape analysis, it should be as important as the mono-$b$ signature. In the region of relatively low mediator mass (below a few hundred GeV), by requiring the signal to background ratio greater than a few percent, the 2$b$-tagged razor analysis has comparable sensitivity to the mono-$b$ search; it is even better for mediator lighter than $\sim 200$ GeV.

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arXiv2016

$H_{u,d}$-messenger Couplings Address the $μ/B_μ$ \& $A_t/m_{H_u}^2$ Problem and $(g-2)_μ$ Puzzle

Gauge mediated supersymmetry (SUSY)-breaking (GMSB) furnishes the best idea to overcome the flavor problem in SSMs, supersymmetric stand models (SM). However, implemented in the minimal SSM (MSSM), a very serious fine-tuning problem arises, owing to the absence of a large $A_t$ term in the stop sector to radiatively enhance the SM-like Higgs boson mass. In the extended GMSB coupling $H_u$ to messengers can alleviate this problem but encounters the $A_t/m_{H_u}^2$ problem, i.e., at the same time a large $m_{H_u}^2$ is generated, rendering radiative electroweak spontaneously breaking (EWSB) problematic. This issue shows similarity to another long-standing problem of GMSB, the $μ/{B_μ}$ problem, and, of great interest, we find that they may admit the same solution, nonradiative EWSB. Such a solution is naturally accommodated when both $H_u$ and $H_d$ couple to messengers. As a bonus of nonradiative EWSB, the sleptons tend to be very light due to the significant renormalization group equation effect and they are able to account for the $(g-2)_μ$ puzzle. As a concrete example, we investigate a hidden sector with $(10,\overline {10})$ messengers.

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arXiv2016

Oscillating Asymmetric Sneutrino Dark Matter from the Maximally $U(1)_L$ Supersymmetric Inverse Seesaw

The inverse seesaw mechanism provides an attractive approach to generate small neutrino mass, which origins from a tiny $U(1)_L$ breaking. In this paper, we work in the supersymmetric version of this mechanism, where the singlet-like sneutrino could be an asymmetric dark matter (ADM) candidate in the maximally $U(1)_{L}$ symmetric limit. However, even a tiny $δm$, the mass splitting between sneutrino and anti-sneutrino as a result of the tiny $U(1)_{L}$ breaking effect, could lead to fast oscillation between sneutrino and anti-sneutrino and thus spoils the ADM scenario. We study the evolution of this oscillation and find that a weak scale sneutrino, which tolerates a relatively larger $δm\sim 10^{-5}$ eV, is strongly favored. We also investigate possible natural ways to realize that small $δm$ in the model.

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arXiv2016

The Maximal $U(1)_L$ Inverse Seesaw from $d=5$ Operator and Oscillating Asymmetric Sneutrino Dark Matter

The maximal $U(1)_L$ supersymmetric inverse seesaw mechanism (M$L$SIS) provides a natural way to relate asymmetric dark matter (ADM) with neutrino physics. In this paper we point out that, M$L$SIS is a natural outcome if one dynamically realizes the inverse seesaw mechanism in the next-to minimal supersymmetric standard model (NMSSM) via the dimension-five operator $(N)^2S^2/M_*$, with $S$ the NMSSM singlet developing TeV scale VEV; it slightly violates lepton number due to the suppression by the fundamental scale $M_*$, thus preserving $U(1)_L$ maximally. The resulting sneutrino is a distinguishable ADM candidate, oscillating and favored to have weak scale mass. A fairly large annihilating cross section of such a heavy ADM is available due to the presence of singlet.

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arXiv2016

New Avenues to Heavy Right-handed Neutrinos with Pair Production at Hadronic Colliders

In many models incorporating the type-I seesaw mechanism, the right-handed neutrino ($N$) couples to heavy vector/scalar bosons and thereby has resonant pair production. It barely receives attention thus far, however, it may provide the best avenue to probe TeV scale $N$ without requiring anomalously large mixing between $N$ and the active neutrino $ν_L$. In this paper we explore the discovery prospects of (mainly heavy) $N$ pair production at the 14 TeV LHC and future 100 TeV $pp$ collider, based on the three signatures: 1) trilepton from $ N(\rightarrow \ell W_\ell)N(\rightarrow \ell W_h)$ with $W_{\ell/h}$ the leptonically/hadronically decaying $W$; 2) boosted di-Higgs boson plus MET from $N(\rightarrow ν_L h)N(\rightarrow ν_L h)$; 3) a single boosted Higgs with leptons and MET from $N(\rightarrow \ell W_\ell)N(\rightarrow ν_L h)$. At the 100 TeV collider, we also consider the situation when the Higgs boson is over boosted thus losing its jet substructure. Interpreting our tentative results in the benchmark model, the local $B-L$ model, we find that the (multi-) TeV scale $N$ can be probed at the (100) 14 TeV colliders.

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arXiv2016

New Physics Opportunities in the Boosted Di-Higgs plus \ET Signature

The Higgs field in the standard model (SM) may couple to new physics sectors related with dark matter and/or massive neutrinos. In this paper we propose a novel signature, the boosted di-Higgs boson plus \ET (which is either a dark matter or neutrino), to probe those new physics sectors. In a large class of models, in particular the supersymmetric SMs and low scale seesaw mechanisms, this signature can play a key role. The signature has clear background, and at the $\sqrt s=$14 TeV high luminosity (HL-)LHC, we can probe it with production rate as low as $\sim$ 0.1 fb. We apply it to benchmark models, supersymmetry in the bino-Higgsino limit, the canonical seesaw model and little Higgs model, finding that masses of Higgsino, right-handed neutrino and heavy vector boson can be probed up to $\sim$ 500 GeV, 650 GeV and 900 GeV, respectively.

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arXiv2016

Naturally Large Radiative Lepton Flavor Violating Higgs Decay Mediated by Lepton-flavored Dark Matter

In the standard model (SM), lepton flavor violating (LFV) Higgs decay is absent at renormalizable level and thus it is a good probe to new physics. In this article we study a type of new physics that could lead to large LFV Higgs decay, i.e., a lepton-flavored dark matter (DM) model which is specified by a Majorana DM and scalar lepton mediators. Different from other similar models with similar setup, we introduce both left-handed and right-handed scalar leptons. They allow large LFV Higgs decay and thus may explain the tentative Br$(h\raτμ)\sim1\%$ experimental results from the LHC. In particular, we find that the stringent bound from $τ\raμγ$ can be naturally evaded. One reason, among others, is a large chirality violation in the mediator sector. Aspects of relic density and especially radiative direct detection of the leptonic DM are also investigated, stressing the difference from previous lepton-flavored DM models.

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arXiv2015

LHC $τ$-rich Tests of Lepton-specific 2HDM for $(g-2)_μ$

The lepton-sepcific (or type X) 2HDM (L2HDM) is an attractive new physics candidate explaining the muon $g-2$ anomaly requiring a light CP-odd boson $A$ and large $\tanβ$. This scenario leads to $τ$-rich signatures, such as $3τ$, $4τ$ and $4τ+W/Z$, which can be readily accessible at the LHC. We first study the whole L2HDM parameter space to identify allowed regions of extra Higgs boson masses as well as two couplings $λ_{hAA}$ and $ξ_h^l$ which determine the 125 GeV Higgs boson decays $h\to τ^+τ^-$ and $h\to AA/AA^*(τ^+τ^-)$, respectively. This motivates us to set up two regions of interest: (A) $m_A \ll m_{H} \sim m_{H^\pm}$, and (B) $m_A \sim m_{H^\pm} \sim {\cal O}(100) \mbox{GeV} \ll m_H$, for which derive the current constraints by adopting the chargino-neutralino search at the LHC8, and then analyze the LHC14 prospects by implementing $τ$-tagging algorithm. A correlated study of the upcoming precision determination of the 125 GeV Higgs boson decay properties as well as the observation of multi-tau events at the next runs of LHC will be able to shed light on the L2HDM option for the muon $g-2$.

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