Twin Symmetry Research Articles

A Portalino to the Twin Sector

Extensions of the Standard Model are often highly constrained by cosmology. New states in the theory can dramatically alter observed properties of the universe by the presence of additional matter or entropy. In particular, attempts to solve the hierarchy problem through naturalness invariably predict new particles near the weak scale which come into thermal equilibrium. Without a means to deposit this energy into the SM, these models are often excluded. Scenarios of “neutral naturalness” in particular, such as the Twin Higgs, frequently suffer from this. However, the Portalino, a singlet fermion that marries gauge neutral fermion operators, can naturally help provide a portal for entropy to return to the SM and to lift fermionic degrees of freedom in the Twin Sector. Together with spontaneous breaking of the Z2 SM ↔ Twin symmetry, there are new opportunities to confront the cosmological challenges of these models. Here, we attempt to develop such ideas. We shall show how one can lift many of the light fields by breaking Z2 with a U(1)Y scalar and its Twin partner. The introduction of Portalinos can lift the remaining degrees of freedom. We shall find that such models are highly constrained by precision SM measurements, motivating moderate extensions beyond this. We will discuss two, both of which include Z2 breaking, one with additional electroweak matter and another with additional colored matter. The electroweak model will involve simple dim-6 operators, which are easily UV completed. The strong model will involve the presence of new leptoquarks and diquarks. We will discuss the implications for the observed value of the muon anomalous magnetic moment, contributions to μ → eγ decay and possible colored signals even within these models of neutral naturalness, some of which might appear at the LHC or future colliders.

Atomic-scale mechanism of rhombohedral twinning in sapphire

Deformation twinning is a fundamental plastic deformation mode in crystals. Upon twinning, individual atoms must move in different directions to satisfy the twin symmetry, which is called atomic shuffling. However, actual atomic motions during shuffling are still unknown, especially for ionic compounds. Here, we report the dynamic twinning behavior dominated by the atomic shuffling in sapphire (α-Al2O3). The propagation and annihilation of twins are revealed to be mediated by migration of step structures on the matrix/twin interfaces. The step migration is driven by cooperative motions of a group of five atoms with relatively few recombination of Al–O bonds. Our findings imply that the atomic shuffling associated with twinning is determined by a collective property of a group of several atoms.

High-temperature electroweak symmetry breaking by SM twins

We analyse a possible adjustment of Twin Higgs models allowing to have broken electroweak (EW) symmetry at all temperatures below the sigma-model scale ∼ 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 Higgs models, but still less tuning than the usual pseudo-Nambu-Goldstone Higgs models not improved by Z2 twin symmetry. The obtained modification in the evolution of the EW symmetry breaking strength can, in particular, have interesting implications for models of EW baryogenesis, which we comment on.

Ferroelastic domains and phase transitions in organic–inorganic hybrid perovskite CH3NH3PbBr3

Polarized light microscopy reveals twin domains and symmetry of the phases in CH3NH3PbBr3 crystal; domain structure remains unresponsive to electric field but changes under external stress, confirming ferroelasticity while ruling out ferroelectricity.

Spontaneous twin symmetry breaking

We consider a twin Higgs scenario where the $Z_2$ twin symmetry is broken spontaneously, not explicitly. This scenario provides an interesting interpretation of the Higgs metastability in the standard model; the $SU(4)$ breaking scale $f$ is determined by the scale where the Higgs self quartic coupling flips its sign. However, for the misalignment of nonzero vacuum expectation values of the twin Higgs fields, parameter tuning of ${\cal O}(m_h^2/f^2)$ is required like explicit twin symmetry breaking scenarios. For the minimal model with the exact twin symmetry, $f$ is ${\cal O}$($10^{10}$ GeV), so the model is very unnatural. We point out that the tuning can be significantly reduced ($f\gtrsim 2.7$ TeV) if there are twin vector-like leptons with large Yukawa coupling to twin Higgs fields.

Investigation of an Unusual Crystal Habit of Hydrochlorothiazide Reveals Large Polar Enantiopure Domains and a Possible Crystal Nucleation Mechanism

AbstractThe observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro‐XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit‐cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.

Investigation of an Unusual Crystal Habit of Hydrochlorothiazide Reveals Large Polar Enantiopure Domains and a Possible Crystal Nucleation Mechanism.

The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro-XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit-cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.

Adding Symmetry: Cylindrically Confined Crystallization of Nylon-6

It has been known that twin symmetry occurs in small metal crystals and it could lead to ultrahigh mechanical properties. In this research, we first found out the formation of nanoscale twin crystals in polymers under cylindrical confinement. The nylon-6 nanorods are fabricated by infiltrating the melt into cylindrical nanopores of an anodized alumina oxide template. The α-phase nanotwin of nylon-6 under cylindrical confinement has been examined by both two-dimensional wide-angle X-ray diffraction and transmission electron microscopy (TEM) selected-area electron diffraction (SAED) techniques. The 45° angle between two 200 reflections in the TEM SAED pattern of individual nylon-6 nanorods precisely confirms that nanocrystals in the nylon-6 rod are twins. The twin axis is along the a-axis orientation, which is also the hydrogen-bond direction of the unit cell. The (001) composition (twin) plane is the hydrogen-bonded sheet.

Twin Turtles

We present an ultraviolet extension of the Twin Higgs in which the radial mode of twin symmetry breaking is itself a pseudo-goldstone boson. This “turtle” structure raises the scale of new colored particles in exchange for additional states in the Higgs sector, making multiple Higgs-like scalars the definitive signature of naturalness in this context. We explore the parametrics and phenomenology of a concrete Twin Turtle model and demonstrate its robustness in two different supersymmetric completions. Along the way, we also introduce a new mechanism for inducing hard twin symmetry-breaking quartics via soft supersymmetry breaking.

The composite twin Higgs scenario

Based on an explicit model, we propose and discuss the generic features of a possible implementation of the Twin Higgs program in the context of composite Higgs models. We find that the Twin Higgs quadratic divergence cancellation argument can be uplifted to a genuine protection of the Higgs potential, based on symmetries and selection rules, but only under certain conditions which are not fulfilled in some of the existing models. We also find that a viable scenario, not plagued by a massless Twin Photon, can be obtained by not gauging the Twin Hypercharge and taking this as the only source of Twin Symmetry breaking at a very high scale.

Response to “Comment on ‘Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate’ ” [J. Appl. Phys. 112, 016101 (2012)

Welander is correct about the misidentified crystal-directions in the top-view sapphire lattice (Fig. 4 [Zhao et al., J. Appl. Phys. 110, 033523 (2011)]). He is also correct about the misorientation of the pole figures in Fig. 4. In Fig. 1 of this response, we have corrected these errors. Perhaps because of these errors, Welander misconstrued our discussion of the Nb crystal growth as claiming a new 3D registry. That was not our intention. Rather, we wished to highlight the role of energetic condensation that drives low-defect crystal growth by a combination of non-equilibrium sub-plantation that disturbs the substrate lattice and thermal annealing that annihilates defects and promotes large-grain crystal growth.

Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3)

An energetic condensation technique, cathodic arc discharge deposition, is used to grow epitaxial Niobium (Nb) thin films on a-plane sapphire (hexagonal-closed-packed Al2O3) at moderate substrate heating temperature (<400 °C). The epitaxial Nb(110)/Al2O3(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nb cathode source whose RRR was only 30. The measurements suggest that the film’s density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nb thin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3 three-dimensional epitaxial relationship (“3D-Registry” Claassen’s nomenclature) and the “Volmer-Weber” (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films’ topmost surface (∼50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. A possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

Twin symmetry roll axial rolling: new method of plastic forming profiles demonstrated using manufacture of spiral bevel gears

When using conventional manufacturing methods for machining gears, the percentage of stock material utilisation in the finished article is low due to the amount of swarf removed during machining. In addition, the machining process itself may result in low tooth strength. Adopting a plastic forming method to produce gear forms can greatly enhance the mechanical properties of the product. The size of the automotive transmission driven by a rear axle spiral bevel gear which is used as a case study in this paper is larger than that usually manufactured by the plastic forming method. Objects of this size require high capacity hot forming equipment, and even then it is difficult to obtain a full profile. In this paper, a new method of plastic forming profiles: twin symmetry roll axial rolling is described using a spiral bevel gear as a case study. The technology was analysed by producing a three‐dimensional model of the spiral bevel gear, and finite element analysis was used to simulate the process. It can be seen that the teeth were completely filled with a well defined outline and only a small amount of horizontal overfilling and vertical flash occurred because there was small contact area between the blank and rolls which minimised the rolling force.

Reticular merohedral twinning within the La9Sb5O5 structure family: structure of Pr9Sb5O5, Sm9Sb5O5 and Dy9Sb5O5

The novel antimonide oxides Pr(9)Sb(5)O(5), Sm(9)Sb(5)O(5) and Dy(9)Sb(5)O(5) were synthesized from the respective RESb, the rare-earth metals (RE = Pr, Sm, Dy), and RE(2)O(3) (RE = Sm, Dy) or Pr(4)O(7), respectively, in sealed tantalum ampoules at 1920 K. Those compounds, which are sensitive against air and moisture, form black cube-like crystals with metallic lustre. They crystallize in the La(9)Sb(5)O(5) type of structure, which represents a fivefold superstructure of the KCoO(2) structure: O(10)K(5)Co(5)[sign: see text]La(9)[sign: see text]Sb(5)O(5). The investigated crystals of the Sm and Dy compounds were twinned using the reticular merohedral law, with the twin symmetry 4/mm'm', and the (310) and (120) mirror planes as twinning symmetry elements. The twin index is [j] = 5.

Contribution to the crystal chemistry of rare earth chalcogenides. III. The crystal structure and twinning of SmS1.9

The structure of samarium disulfide SmS1.9, space group P42/n; lattice constants a = 19.717(2)Å ; c = 15.928(1) Å has been determined and refined by LS method to R = 0.0345; Rw = 0.0419. The structure is a tenfold superstructure from the structure type ZrSSi. [S2]2– dumbbells with interatomic distances 2.146(1)Å between S atoms were observed in the structure. Fully ordered vacancies and orientation of the [S2]2- dumbbells are responsible for the formation of the superstructure. The investigated sample was twinned by the reticular merohedral law, the twin symmetry is 4/mm´m´, the twinning symmetry elements are (310) and (120) mirror planes and the twin index is n=5.

Contribution to the crystal chemistry of rare-earth chalcogenides. II The crystal structure and twinning of rare-earth diusulfide PrS2

The structure of the presodyme disulfide PrS2 has been determined and refined by the LS method in space group P21/b11(14) with a=4.054(1) Å; b=8.058(1) Å; c=8.079(1) Å and α=90.08(2)° to the final values of discrepancy factors R=0.188; Rw=0.0204. The structure is a derivative structure of the ZrSSi (or PbFCl) structure type. A heringbone pattern of S2 2- dumbbells with interatomic distance 2.135(1) Å is observed in the planes parallel to (001). The investigated crystal has been twinned by pseudomerohedral law, the twin symmetry is mm’m‘ and the twinning symmetry elements are (010) and (001) mirror planes.

On magnetic domain twin symmetry

A magnetic domain twin consists of two magnetic domains which meet along a planar transition region called a domain wall. The symmetry of a magnetic domain twin consists of those symmetry elements which 1) leave both domains invariant and also leave invariant the normal to the domain wall or 2) interexchange the domains and invert the normal. The magnetic domain symmetry is a magnetic layer group. It is shown how forthcoming tables of the non-magnetic sectional layer groups of non-magnetic crystals (International Tables for Crystallography, Volume E (Kopsky and Litvin)) can be used to determine possible magnetic domain twin symmetry.

Macroscopic symmetry group describes Josephson tunneling in twinned crystals

A macroscopic symmetry group describing the superconducting state of an orthorhombically twinned crystal of YBCO is introduced. This macroscopic symmetry group is different for different symmetries of twin boundaries. Josephson tunneling experiments performed on twinned crystals of YBCO determine this macroscopic symmetry group and hence determine the twin boundary symmetry (but do not experimentally determine whether the microscopic order parameter is primarily d- or s-wave). A consequence of the odd-symmetry twin boundaries in YBCO is the stability of 1/2 Φo vortices at the intersection of a twin boundary and certain grain boundaries.

On basal slip and basal twinning in sapphire (α-Al 2O 3)—I. Basal slip revisited

The motion of partial dislocations ( b = 1/3 [011¯0〉 and 1/3 [101¯0〉) uvtw〉 refers to the direction [ uvtw] and the two equivalent directions related by the 3-fold rotational symmetry about [0001]. 1/3 〈112¯0〉) in sapphire (α-Al 2O 3 is analysed. Crystallographic arguments suggest that the basal slip plane should be a plane passing through the normally-vacant octahedral sites defined by the anion sublattice. This definition of the basal slip plane implies that half of the cations lying between two adjacent anion layers are above and the other half are below the slip plane. The stacking faults that would be created by the motion of a dissociated basal dislocation differs in structure and energy, depending on whether the 1/3 [101¯0〉 partial is leading or trailing. Thus, the motion of a 1/3 [101¯0〉 partial in its favorable (lower energy) direction creates a stacking fault with a stacking sequence in which the cations are in a localized twin symmetry, whereas the motion of a 1/3 [101¯0〉 partial in its unfavorable (higher energy) direction is “forbidden”. Furthermore, the motion of a 1/3 [101¯0〉 partial in its favorable direction can take place without the need for synchroshear.

Reflectivity anisotropy of superconducting YBa 2Cu 3O7− x single crystals in the a- b plane

Polarized reflectivity spectra of orthorhombic and tetragonal YBa 2Cu 3 O 7− x crystals in the 1–3 eV range were studied. Two types of anisotropy of optical properties (reflection) in the a- b plane were observed for superconducting orthorhombic crystals. The first is attributable to the crystal symmetry and reflects the nonequivalence of the a and b axes. The other type of anisotropy appears in the twinned regions of the crystal and is governed by the twin symmetry.