We study the tagging of Higgs exotic decay signals using different types of deep neural networks (DNNs), focusing on the $W^pm h$ associated production channel followed by Higgs decaying into $n$ $b$-quarks with $n=4$, 6 and 8. All the Higgs decay pr
oducts are collected into a fat-jet, to which we apply further selection using the DNNs. Three kinds of DNNs are considered, namely convolutional neural network (CNN), recursive neural network (RecNN) and particle flow network (PFN). The PFN can achieve the best performance because its structure allows enfolding more information in addition to the four-momentums of the jet constituents, such as particle ID and tracks parameters. Using the PFN as an example, we verify that it can serve as an efficient tagger even though it is trained on a different event topology with different $b$-multiplicity from the actual signal. The projected sensitivity to the branching ratio of Higgs decaying into $n$ $b$-quarks at the HL-LHC are 10%, 3% and 1%, for $n=4$, 6 and 8, respectively.
If the strange quark were lighter, QCD phase transition could have been first order. This implies that QCD may have quantum critical points as the Higgs vev $v_h$ is varied from its Standard Model value. We show that inflationary quantum evolution of
$v_h$ with the relaxion can drive our universe toward those critical points, realizing the weak scale close to the observed value while explaining its closeness to $Lambda_{rm QCD}$. We first explore quantum critical points of $N_f=3$ QCD, parameterized by $v_h$ at $T=0$, and present a basic model for the weak scale. It results in a sharply localized probability distribution of the weak scale, which is critical not to the crossover at zero but to the quantum transition at ${sim}Lambda_{rm QCD}$.
The small CMB amplitude $A_s simeq 10^{-9}$ (or, small temperature fluctuation $delta T/T simeq 10^{-5}$) typically requires an unnaturally small effective coupling of an inflaton $lambda_phi sim 10^{-14}$. In successful models, there usually is extr
a suppression of the amplitude, e.g. by large-field inflaton with non-minimal coupling $xi$, so that $lambda_phi$ can be much larger. But $lambda_phi$ and $xi$ cannot be $sim {cal O}(1)$ simultaneously; the naturalness burden is shared between them. We show that the absence of new physics signals at TeV scale may prefer a more natural size of $xi lesssim {cal O}(1-100)$ with $lambda_phi lesssim {cal O}(10^{-4}-10^{-8})$, constraining larger $xi$ with larger $lambda_phi$ more strongly. This intriguing connection between low- and high-energy physics is made in the scenarios with $U(1)_X$ where inflatons renormalization running also induces Coleman-Weinberg mechanism for the electroweak symmetry breaking. We particularly work out the prospects of LHC 13 and 100 TeV $pp$ colliders for probing the parameter space of the small CMB amplitude.
Subhalos at subgalactic scales ($Mlesssim 10^7 M_odot$ or $kgtrsim 10^3 ,{rm Mpc}^{-1}$) are pristine test beds of dark matter (DM). However, they are too small, diffuse and dark to be visible, in any existing observations. In this paper, we develop
a complete formalism for weak and strong diffractive lensing, which can be used to probe such subhalos with chirping gravitational waves (GWs). Also, we show that Navarro-Frenk-White(NFW) subhalos in this mass range can indeed be detected individually, albeit at a rate of ${cal O}(10)$ or less per year at BBO and others limited by small merger rates and large required SNR $gtrsim 1/gamma(r_0) sim 10^3$. It becomes possible as NFW scale radii $r_0$ are of the right size comparable to the GW Fresnel length $r_F$, and unlike all existing probes, their lensing is more sensitive to lighter subhalos. Remarkably, our formalism further reveals that the frequency dependence of weak lensing (which is actually the detectable effect) is due to shear $gamma$ at $r_F$. Not only is it consistent with an approximate scaling invariance, but it also offers a new way to measure the mass profile at a successively smaller scale of chirping $r_F propto f^{-1/2}$. Meanwhile, strong diffraction that produces a blurred Einstein ring has a universal frequency dependence, allowing only detections. These are further demonstrated through semianalytic discussions of power-law profiles. Our developments for a single lens can be generalized and will promote diffractive lensing to a more concrete and promising physics in probing DM and small-scale structures.
We propose a novel dark matter (DM) scenario based on a first-order phase transition in the early universe. If dark fermions acquire a huge mass gap between true and false vacua, they can barely penetrate into the new phase. Instead, they get trapped
in the old phase and accumulate to form macroscopic objects, dubbed Fermi-balls. We show that Fermi-balls can explain the DM abundance in a wide range of models and parameter space, depending most crucially on the dark-fermion asymmetry and the phase transition energy scale (possible up to the Planck scale). They are stable by the balance between fermions quantum pressure against free energy release, hence turn out to be macroscopic in mass and size. However, this scenario generally produces no detectable signals (which may explain the null results of DM searches), except for detectable gravitational waves (GWs) for electroweak scale phase transitions; although the detection of such stochastic GWs does not necessarily imply a Fermi-ball DM scenario.
This paper presents a combined analysis of the potential of a future electron-positron collider to constrain the Higgs, top and electro-weak (EW) sectors of the Standard Model Effective Field Theory (SMEFT). The leading contributions of operators inv
olving top quarks arise mostly at one-loop suppressed order and can be captured by the renormalization group mixing with Higgs operators. We perform global fits with an extended basis of 29 parameters, including both Higgs and top operators, to the projections for the Higgs, top and electro-weak precision measurements at the International Linear Collider (ILC). The determination of the Higgs boson couplings in the 250 GeV stage of the ILC is initially severely degraded by the additional top-quark degrees of freedom, but can be nearly completely recovered by the inclusion of precise measurements of top-quark EW couplings at the LHC. The physical Higgs couplings are relatively robust, as the top mass is larger than the energy scale of EW processes. The effect of the top operators on the bounds on the Wilson coefficients is much more pronounced and may limit our ability to identify the source of deviations from the Standard Model. Robust global bounds on all Wilson coefficients are only obtained when the 500 GeV stage of the ILC is included.
The axion-gravity Chern-Simons coupling is well motivated but is relatively weakly constrained, partly due to difficult measurements of gravity. We study the sensitivity of LIGO measurements of chirping gravitational waves (GWs) on such coupling. Whe
n the frequency of the propagating GW matches with that of the coherent oscillation of axion dark matter field, the decay of axions into gravitons can be stimulated, resonantly enhancing the GW. Such a resonance peak can be detected at LIGO as a deviation from the chirping waveform. Since all observed GWs will undergo similar resonant enhancement from the Milky-Way (MW) axion halo, LIGO O1+O2 observations can potentially provide the strongest constraint on the coupling, at least for the axion mass $m_a = 5 times 10^{-13} - 5 times 10^{-12}$ eV. Along the course, we also emphasize the relevance of the finite coherence of axion fields and the ansatz separating forward and backward propagations of GWs. As a result, the parity violation of the Chern-Simons coupling is not observable from chirping GWs.
We study the $h gamma Z$ coupling, which is a loop induced coupling in the Standard Model (SM), to probe new physics. In a global fit based on the SM Effective Field Theory, measurement of the SM $h gamma Z$ coupling can provide a very useful constra
int, in particular for the precise determination of $hZZ$ and $hWW$ couplings. At the International Linear Collider (ILC), there are two direct ways to study the $h gamma Z$ coupling: one is to measure the branching ratio of the $h to gamma Z$ decay and the other to measure the cross section for the $e^+e^- to h gamma$ process. We have performed a full simulation study of the $e^+e^- to h gamma$ process at the 250 GeV ILC, assuming 2 ab$^{-1}$ data collected by the International Large Detector (ILD). The expected 1$sigma$ bound on the effective $hgamma Z$ coupling ($zeta_{AZ}$) combining measurements of the cross section for $e^+e^- to h gamma$ followed by $h to b bar{b}$ and the $h to gamma Z$ branching ratio is $-0.0015<zeta_{AZ}<0.0015$. The expected significance for the signal cross section in the fully hadronic $h to WW^*$ channel is 0.09 $sigma$ for beam polarizations of $P(e^-,e^+)=(-80%,+30%)$.
The primordial black hole (PBH) comprising full dark matter (DM) abundance is currently allowed if its mass lies between $10^{-16}M_{odot} lesssim M lesssim 10^{-11} M_{odot}$. This lightest mass range is hard to be probed by ongoing gravitational le
nsing observations. In this paper, we advocate that an old idea of the lensing parallax of Gamma-ray bursts (GRBs), observed simultaneously by spatially separated detectors, can probe the unconstrained mass range; and that of nearby stars can probe a heavier mass range. In addition to various good properties of GRBs, astrophysical separations achievable around us --- $r_oplus text{--}$ AU --- is just large enough to resolve the GRB lensing by lightest PBH DM.
The Twin Higgs model provides a natural theory for the electroweak symmetry breaking without the need of new particles carrying the standard model gauge charges below a few TeV. In the low energy theory, the only probe comes from the mixing of the Hi
ggs fields in the standard model and twin sectors. However, an ultraviolet completion is required below ~ 10 TeV to remove residual logarithmic divergences. In non-supersymmetric completions, new exotic fermions charged under both the standard model and twin gauge symmetries have to be present to accompany the top quark, thus providing a high energy probe of the model. Some of them carry standard model color, and may therefore be copiously produced at current or future hadron colliders. Once produced, these exotic quarks can decay into a top together with twin sector particles. If the twin sector particles escape the detection, we have the irreducible stop-like signals. On the other hand, some twin sector particles may decay back into the standard model particles with long lifetimes, giving spectacular displaced vertex signals in combination with the prompt top quarks. This happens in the Fraternal Twin Higgs scenario with typical parameters, and sometimes is even necessary for cosmological reasons. We study the potential displaced vertex signals from the decays of the twin bottomonia, twin glueballs, and twin leptons in the Fraternal Twin Higgs scenario. Depending on the details of the twin sector, the exotic quarks may be probed up to ~ 2.5 TeV at the LHC and beyond 10 TeV at a future 100 TeV collider, providing a strong test of this class of ultraviolet completions.
