我们研究了镜像双希格斯（Mirror Twin Higgs，MTH）框架下一种自然的非对称暗物质（asymmetric dark matter，ADM）模型。研究表明，当双重子作为暗物质（DM）候选者时，无需在无量纲耦合中显式破坏MTH的$\n\b_2$对称性（即无硬$\n\b_2$破缺），即可得到符合观测的暗物质丰度。我们通过一个同时产生非对称暗物质的特定重子生成机制，阐释了该过程的实现原理。在最简方案中，我们得到暗物质质量$m_{\rm DM}\sim O(1)$GeV，略高于质子质量。本文还给出了当前及未来实验的直接探测率估算结果。
英文摘要：
We consider a natural asymmetric dark matter (ADM) model in the mirror twin Higgs (MTH). We show that it is possible to obtain the correct dark matter (DM) abundance when a twin baryon is the DM without the need of explicit breaking of the MTH $\mathbb{Z}_2$ symmetry in the dimensionless couplings (i.e. without hard $\mathbb{Z}_2$ breaking). We illustrate how this is possible in a specific baryogenesis setup, which also leads to ADM. In the simplest scenario we obtain $m_{\rm DM}\sim O(1)$GeV, just above the proton mass. We show estimates for direct detection rates at present and future experiments.
In the context of Twin Higgs models, we study a simple mechanism that simultaneously generates asymmetries in the dark and visible sector through the out-of-equilibrium decay of a TeV scale particle charged under a combination of baryon and twin baryon number. We predict the dark matter to be a 5 GeV twin baryon, which is easy to achieve because of the similarity between the two confinement scales. Dark matter is metastable and can decay to three quarks, yielding indirect detection signatures. The mechanism requires the introduction of a new colored particle, typically within the reach of the …
The paper suggests a left-right mirror symmetric model to account for the baryogenesis and asymmetric dark matter. The model can simultaneously accommodate the standard model, neutrino physics, matter-antimatter asymmetry and dark matter. In particular, it naturally and elegantly explains the origin of the baryon and dark matter asymmetries, and clearly gives the close interrelations of them. In addition, the model predicts a number of interesting results, e.g. the cold dark matter neutrino mass is $3.1$ times the proton mass. It is also feasible and promising to test the model in future exper…
Models of asymmetric dark matter (ADM) seek to explain the apparent coincidence between the present-day mass densities of visible and dark matter, $Ω_{\mathrm{DM}} \simeq 5Ω_{\mathrm{VM}}$. However, most ADM models only relate the number densities of visible and dark matter without motivating the similar particle masses. We expand upon a recent work that obtained a natural mass relationship in a mirror matter ADM model with two Higgs doublets in each sector, by looking to implement dark electroweak baryogenesis as the means of asymmetry generation. We explore two aspects of the mechanism: the …
We consider the collider signals arising from kinetic mixing between the hypercharge gauge boson of the Standard Model and its twin counterpart in the Mirror Twin Higgs model, in the framework in which the twin photon is massive. Through the mixing, the Standard Model fermions acquire charges under the mirror photon and the mirror Z boson. We determine the current experimental bounds on this scenario, and show that the mixing can be large enough to discover both the twin photon and the twin Z at the LHC, or at a future 100 TeV hadron collider, with dilepton resonances being a particularly cons…
The twin Higgs mechanism is a solution to the little hierarchy problem in which the top partner is neutral under the Standard Model (SM) gauge group. The simplest mirror twin Higgs (MTH) model -- where a $\mathbf{Z}_2$ symmetry copies each SM particle -- has too many relativistic degrees of freedom to be consistent with cosmological observations. We demonstrate that MTH models can have an observationally viable cosmology if the twin mass spectrum leads to twin neutrino decoupling before the SM and twin QCD phase transitions. Our solution requires the twin photon to have a mass of $\sim 20$ MeV…
In addition to being a solution to the little hierarchy problem, the Mirror Twin Higgs provides a natural setting for Asymmetric Dark Matter. In its incarnation with only one Higgs doublet and its mirror copy, dark matter would however almost certainly consist mostly of mirror atoms, which is severely ruled out by constraints on dark matter self-interactions. By adding a second Higgs doublet and its mirror, the vevs of the different Higgses can be arranged such that dark matter consists mostly of mirror neutrons, which is cosmologically viable. In this paper, it is shown that current constrain…
In a Mirror Twin World with a maximally symmetric Higgs sector the little hierarchy of the Standard Model can be significantly mitigated, perhaps displacing the cutoff scale above the LHC reach. We show that consistency with observations requires that the Z2 parity exchanging the Standard Model with its mirror be broken in the Yukawa couplings. A minimal such effective field theory, with this sole Z2 breaking, can generate the Z2 breaking in the Higgs sector necessary for the Twin Higgs mechanism. The theory has constrained and correlated signals in Higgs decays, direct Dark Matter Detection a…
We investigate simple extensions of the Mirror Twin Higgs model in which the twin color gauge symmetry and the discrete $Z_2$ mirror symmetry are spontaneously broken. This is accomplished in a minimal way by introducing a single new colored triplet, sextet, or octet scalar field and its twin along with a suitable scalar potential. This spontaneous $Z_2$ breaking allows for a phenomenologically viable alignment of the electroweak vacuum, and leads to dramatic differences between the visible and mirror sectors with regard to the residual gauge symmetries at low energies, color confinement scale…
We argue that presymmetry, a hidden predynamical electroweak quark-lepton symmetry that explains the fractional charges and triplication of families, must be extended beyond the Standard Model as to have a residual presymmetry that embraces partner particles and includes the strong sector, so accounting for the twin or mirror partners proposed to alleviate the naturalness problem of the weak scale. It leads to the full duplication of fermions and gauge bosons of the Standard Model independently of the ultraviolet completion of the theory, even if the Higgs particle is discarded by experiment, …
We explore the cosmological signatures associated with the twin baryons, electrons, photons and neutrinos in the Mirror Twin Higgs framework. We consider a scenario in which the twin baryons constitute a subcomponent of dark matter, and the contribution of the twin photon and neutrinos to dark radiation is suppressed due to late asymmetric reheating, but remains large enough to be detected in future cosmic microwave background (CMB) experiments. We show that this framework can lead to distinctive signals in large scale structure and in the cosmic microwave background. Baryon acoustic oscillati…
We investigate the cosmology of the minimal model of neutral naturalness, the mirror Twin Higgs. The softly-broken mirror symmetry relating the Standard Model to its twin counterpart leads to significant dark radiation in tension with BBN and CMB observations. We quantify this tension and illustrate how it can be mitigated in several simple scenarios that alter the relative energy densities of the two sectors while respecting the softly-broken mirror symmetry. In particular, we consider both the out-of-equilibrium decay of a new scalar as well as reheating in a toy model of twinned inflation, …
The decay t -> c V (V=γ, Z, g) process in the mirror twin Higgs models with the colorless top partners are studied in this paper. We found that the branching ratios of these decays can in some parameter spaces alter the standard model expectations greatly and may be detectable according to the currently precision electroweak measurements. Thus, the constraints on the model parameters may be obtained from the branching fraction of the decay processes, which may serve as a robust detection to this new physics model.
We explore the possibility of discovering the mirror baryons and electrons of the Mirror Twin Higgs model in direct detection experiments, in a scenario in which these particles constitute a subcomponent of the observed DM. We consider a framework in which the mirror fermions are sub-nano-charged, as a consequence of kinetic mixing between the photon and its mirror counterpart. We consider both nuclear recoil and electron recoil experiments. The event rates depend on the fraction of mirror DM that is ionized, and also on its distribution in the galaxy. Since mirror DM is dissipative, at the lo…
We explore a simple solution to the cosmological challenges of the original Mirror Twin Higgs (MTH) model that leads to interesting implications for experiment. We consider theories in which both the standard model and mirror neutrinos acquire masses through the familiar seesaw mechanism, but with a low right-handed neutrino mass scale of order a few GeV. In these $ν$MTH models, the right-handed neutrinos leave the thermal bath while still relativistic. As the universe expands, these particles eventually become nonrelativistic, and come to dominate the energy density of the universe before dec…
We consider two copies of the Standard Model, interchanged by an exact parity symmetry, P. The observed fermion mass hierarchy is described by suppression factors $ε^{n_i}$ for charged fermion $i$, as can arise in Froggatt-Nielsen and extra-dimensional theories of flavor. The corresponding flavor factors in the mirror sector are $ε'^{n_i}$, so that spontaneous breaking of the parity P arises from a single parameter $ε'/ε$, yielding a tightly constrained version of Minimal Mirror Twin Higgs, introduced in our previous paper. Models are studied for simple values of $n_i$, including in particular…
The Twin Higgs scenario stabilizes the Higgs mass through an approximate global symmetry and has remained natural in the face of increasingly stringent LHC bounds on colored top partners. Two basic structural questions in this framework concern the nature of the twin hypercharge gauge symmetry and the origin of the $\mathbb{Z}_2$ symmetry breaking needed to achieve the correct vacuum alignment. Both questions are addressed in a simple extension of the Mirror Twin Higgs model with an exact $\mathbb{Z}_2$ symmetry and a scalar field that spontaneously breaks both twin hypercharge and $\mathbb{Z}…
We present `twin Higgs models', simple realizations of the Higgs as a pseudo-Goldstone boson that protect the weak scale from radiative corrections up to scales of order 5 - 10 TeV. In the ultra-violet these theories have a discrete symmetry which interchanges each Standard Model particle with a corresponding particle which transforms under a twin or mirror Standard Model gauge group. In addition, the Higgs sector respects an approximate global SU(4) symmetry. When this global symmetry is broken, the discrete symmetry tightly constrains the form of corrections to the pseudo-Goldstone Higgs pot…
We study twin Higgs models at non-zero temperature and discuss cosmological phase transitions as well as their implications on electroweak baryogenesis and gravitational waves. It is shown that the expectation value of the Higgs field at the critical temperature of the electroweak phase transition is much smaller than the critical temperature, which indicates two important facts: (i) the electroweak phase transition cannot be analyzed perturbatively (ii) the electroweak baryogenesis is hardly realized in the typical realizations of twin Higgs models. We also analyze the phase transition associ…
The mirror twin Higgs model (MTH) is a solution to the Higgs hierarchy problem that provides well-predicted cosmological signatures with only three extra parameters: the temperature of the twin sector, the abundance of twin baryons, and the vacuum expectation value (VEV) of twin electroweak symmetry breaking. These parameters specify the behavior of twin radiation and the acoustic oscillations of twin baryons, which lead to testable effects on the cosmic microwave background (CMB) and large-scale structure (LSS). While collider searches can only probe the twin VEV, through a fit to cosmologica…
The cosmology of the Twin Higgs requires the breaking of the $\mathbb{Z}_2$ symmetry, but it is still an open question whether this breaking needs to be explicit. In this paper, we study how the Mirror Twin Higgs could be modified to be compatible with current cosmological constraints without explicit $\mathbb{Z}_2$ breaking. We first present a simple toy model that can realize baryogenesis without explicit $\mathbb{Z}_2$ breaking or reaching temperatures that would lead to domain walls. The model can also either solve the $N_{\text{eff}}$ problem and bring the abundance of mirror atoms to an …
We analyse a possible adjustment of Twin Higgs models allowing to have broken electroweak (EW) symmetry at all temperatures below the sigma-model scale $\sim 1$TeV. The modification consists of increasing the Yukawa couplings of the twins of light SM fermions. The naturalness considerations then imply a presence of relatively light electroweak-charged fermions, which can be produced at the LHC, and decay into SM gauge and Higgs bosons and missing energy. Analysis of experimental bounds shows that such a modified model features an increased amount of fine-tuning compared to the original Twin Hi…
We present an exceptional twin-Higgs model with the minimal symmetry structure for an exact implementation of twin parity along with custodial symmetry. Twin particles are mirrors of the Standard Model yet they carry hypercharge, while the photon is identified with its twin. We thoroughly explore the phenomenological signatures of hypercharged naturalness: long-lived charged particles, a colorless twin top with electric charge $2/3$ that once pair-produced, bounds via twin-color interactions and can annihilate to dileptons or a Higgs plus a photon or a $Z$, and glueballs produced from Higgs de…
We consider Mirror Twin Higgs models in which the breaking of the global symmetry is realized linearly. In this scenario, the radial mode in the Higgs potential is present in the spectrum, and constitutes a second portal between the twin and SM sectors. We show that a study of the properties of this particle at colliders, when combined with precision measurements of the light Higgs, can be used to overdetermine the form of the scalar potential, thereby confirming that it possesses an enhanced global symmetry as dictated by the Twin Higgs mechanism. We find that, although the reach of the LHC f…
The mirror twin Higgs framework allows for a natural Higgs mass while being consistent with collider bounds on colored symmetry partners to standard model quarks. This mechanism relies crucially on a discrete symmetry which relates each standard model field to a mirror partner. These partners are charged under gauge groups identical to, but distinct from, those in the standard model. The minimal twin Higgs scenario provides only one low-energy connection between the visible and twin sectors, the light Higgs boson. We present a new class of portals connecting the two sectors, using fields that …
We present a UV completion of the twin Higgs idea in the framework of holographic composite Higgs. The SM contribution to the Higgs potential is effectively cut off by the SM-singlet mirror partners at the sigma-model scale f, naturally allowing for m_{KK} beyond the LHC reach. The bulk symmetry is SU(7) X SO(8), broken on the IR brane into SU(7) X SO(7) and on the UV brane into (SU(3) X SU(2) X U(1))^{SM} X (SU(3) X SU(2) X U(1))^{mirror} X Z2. The field content on the UV brane is the SM, extended by a sector transforming under the mirror gauge group, with the Z2 exchanging the two sectors. A…
We investigate the general structure of mirror symmetry breaking in the Twin Higgs scenario. We show, using the IR effective theory, that a significant gain in fine tuning can be achieved if the symmetry is broken hardly. We emphasize that weakly coupled UV completions can naturally accommodate this scenario. We analyze SUSY UV completions and present a simple Twin SUSY model with a tuning of around 10% and colored superpartners as heavy as 2 TeV. The collider signatures of general Twin SUSY models are discussed with a focus on the extended Higgs sectors.
Mirror sectors have been proposed to address the problems of dark matter, baryogenesis, and the neutron lifetime anomaly. In this work we study a new, powerful probe of mirror neutrons: neutron star temperatures. When neutrons in the neutron star core convert to mirror neutrons during collisions, the vacancies left behind in the nucleon Fermi seas are refilled by more energetic nucleons, releasing immense amounts of heat in the process. We derive a new constraint on the allowed strength of neutron--mirror-neutron mixing from observations of the coldest (sub-40,000 Kelvin) neutron star, PSR 214…
In twin Higgs models, a discrete Z2 symmetry between the standard model Higgs and the twin Higgs is introduced to address the hierarchy problem. In this work, we propose another discrete symmetry in twin Higgs: the T parity, which maps the twin Higgs quadruplet into its mirror copy. The T parity brings us a whole group of T-odd particles, and leads to a promising dark matter candidate. We present one realization of the T parity twin Higgs scenario by implementing the $SU(2)_L \times SU(2)_R \times U(1)_1 \times U(1)_2$ gauge symmetry in twin Higgs model. In this specific setup, the T-odd U(1) …
Given the lack of empirical evidence of weakly interacting dark matter, it is reasonable to look to other candidates such as a confining dark sector with a similar number of particles as the standard model. Twin Higgs mirror matter is one such model that is a twin of the standard model with particles masses 3--6 times heavier than the standard model that solves the hierarchy problem. This generically predicts mirror neutron stars, degenerate objects made entirely of mirror nuclear matter. We find their structure using a realistic equation of state from crust (nuclei) to core (relativistic mean…
A two Higgs doublet model with flavorful Yukawa structure, in which the two doublets give mass to the third and the first two generations respectively, is combined with the twin Higgs mechanism to stabilize the Higgs mass against radiative corrections. We consider both a mirror twin and fraternal twin setup. We identify Higgs signal strength measurements and the decay $B_s \to μμ$ as the most important indirect constraints on the parameter space of the model. We explore the collider phenomenology of the model and find that the heavy Higgs in the visible sector can give a sizable number of disp…
Twin Higgs models are the prime illustration of neutral naturalness, where the new particles of the twin sector, gauge singlets of the Standard Model (SM), ameliorate the little hierarchy problem. In this work, we analyse phenomenological implications of the heavy Higgs of the Mirror Twin Higgs and Fraternal Twin Higgs models, when electroweak symmetry breaking is linearly realized. The most general structure of twin Higgs symmetry breaking, including explicit soft and hard breaking terms in the scalar potential, is employed. The direct and indirect searches at the LHC are used to probe the pa…
The oscillation of the neutron $n$ into mirror neutron $n'$, its partner from dark mirror sector, can gradually transform an ordinary neutron star into a mixed star consisting in part of mirror dark matter. The implications of the reverse process taking place in the mirror neutron stars depend on the sign of baryon asymmetry in mirror sector. Namely, if it is negative, as predicted by certain baryogenesis scenarios, then $\bar{n}'-\bar{n}$ transitions create a core of our antimatter gravitationally trapped in the mirror star interior. The annihilation of accreted gas on such antimatter cores c…
The mirror twin Higgs (MTH) addresses the little hierarchy problem by relating every Standard Model (SM) particle to a twin copy, but is in tension with cosmological bounds on light degrees of freedom. Asymmetric reheating has recently been proposed as a simple way to fix MTH cosmology by diluting the twin energy density. We show that this dilution sets the stage for an interesting freeze-in scenario where both the initial absence of dark sector energy and the feeble coupling to the SM are motivated for reasons unrelated to dark matter production. We give the twin photon a Stueckelberg mass an…
We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmologica…
Supersymmetric Twin Higgs models have a discrete symmetry for which each Standard Model particle and its supersymmetric partner have a corresponding state that transforms under a mirror Standard Model gauge group. This framework is able to accommodate the non-discovery of new particles at the LHC with the naturalness of the electroweak scale. We point out that supersymmetric Twin Higgs models also provide a natural dark matter candidate. We investigate the possibility that a twin bino-like state is the Lightest Supersymmetric Particle and find that its freeze-out abundance can explain the obse…
B and L violating interactions of ordinary particles with their twin particles from hypothetical mirror world can co-generate baryon asymmetries in both worlds in comparable amounts, $Ω'_B/Ω_B \sim 5$ or so. On the other hand, the same interactions induce the oscillation phenomena between the neutral particles of two sectors which convert e.g. mirror neutrons into our antineutrons. These oscillations are environment dependent and can have fascinating physical consequences.
The Twin Higgs model seeks to address the little hierarchy problem by making the Higgs a pseudo-Goldstone of a global $SU(4)$ symmetry that is spontaneously broken to $SU(3)$. Gauge and Yukawa couplings, which explicitly break $SU(4)$, enjoy a discrete $\mathbb{Z}_2$ symmetry that accidentally maintains $SU(4)$ at the quadratic level and therefore keeps the Higgs light. Contrary to most beyond the Standard Model theories, the quadratically divergent corrections to the Higgs mass are cancelled by a mirror sector, which is uncharged under the Standard Model groups. However, the Twin Higgs with a…
We combine the Twin Higgs mechanism with the paradigm of Composite Higgs models. In this class of models the Higgs is a pseudo-Nambu-Goldstone boson from a strongly coupled sector near the TeV scale, and it is additionally protected by a discrete symmetry due to the twin mechanism. We discuss the model building issues associated with this setup and quantify the tuning needed to achieve the correct electroweak vacuum and the Higgs mass. In contrast to standard Composite Higgs models, the lightest resonance associated with the top sector is the uncolored mirror top, while the colored top partner…
The possibility that a neutron can be transformed to a hidden sector particle remains intriguingly open. Proposed theoretical models conjecture that the hidden sector can be represented by a mirror sector, and the neutron n can oscillate into its sterile mirror twin n', exactly or nearly degenerate in mass with n. Oscillations n - n' can take place in vacuum and in the environment of the regular matter and the magnetic field where only neutron will be subject of interaction with the environment. We describe the propagation of the oscillating n - n' system as a particle of the cold neutron beam…
