High Energy Scale Research Articles

Interstitial-Induced Ferromagnetism in a Two-Dimensional Wigner Crystal.

The two-dimensional Wigner crystal (WC) occurs in the strongly interacting regime (r_{s}≫1) of the two-dimensional electron gas (2DEG). The magnetism of a pure WC is determined by tunneling processes that induce multispin ring-exchange interactions, resulting in fully polarized ferromagnetism for large enough r_{s}. Recently, Hossain etal. [Proc. Natl. Acad. Sci. U.S.A. 117, 32244 (2020)PNASA60027-842410.1073/pnas.2018248117] reported the occurrence of a fully polarized ferromagnetic insulator at r_{s}≳35 in an AlAs quantum well, but at temperatures orders of magnitude larger than the predicted exchange energies for the pure WC. Here, we analyze the large r_{s} dynamics of an interstitial defect in the WC, and show that it produces local ferromagnetism with much higher energy scales. Three hopping processes are dominant, which favor a large, fully polarized ferromagnetic polaron. Based on the above results, we speculate concerning the phenomenology of the magnetism near the metal-insulator transition of the 2DEG.

Effects of Variations of SUSY Breaking Scale on Neutrino Parameters at Low Energy Scale under Radiative Corrections

The paper addresses the effects of the variations of the SUSY breaking scale m s in the range (2-14) TeV on the three neutrino masses and mixings, in running the renormalization group equations (RGEs) for different input values of high energy seesaw scale M R , and in both normal and inverted hierarchical neutrino mass models. The present investigation is a continuation of the earlier works based on the variation of m s scale. Two approaches are adopted one after another—bottom-up approach for running gauge and Yukawa couplings from low to high energy scale, followed by the top-down approach from high to low energy scale for running neutrino parameters defined at high energy scale, along with gauge and Yukawa couplings. A self-complementarity relation among three mixing angles is also employed in the analysis and it is found to be stable under radiative correction. Significant effect due to radiative corrections on neutrino parameters with the variation of SUSY breaking scale m s is observed. For comparison of the results, variation of tan β for different M R is also considered.

New physics in b → sμμ: FCC-hh or a muon collider?

Rare flavour-changing neutral-current transitions b → sμ+μ− probe higher energy scales than what is directly accessible at the LHC. Therefore, the presence of new physics in such transitions, as suggested by the present-day LHCb anomalies, would have a major impact on the motivation and planning of future high-energy colliders. The two most prominent options currently debated are a proton-proton collider at 100 TeV (FCC-hh) and a multi-TeV muon collider (MuC). In this work, we compare the discovery prospects at these colliders on benchmark new physics models indirectly detectable in b → sμ+μ− decays but beyond the reach of the high-pT searches at the HL-LHC. We consider a comprehensive set of scenarios: semileptonic contact interactions, Z′ from a gauged textrm{U}{(1)}_{B_3-{L}_{mu }} and textrm{U}{(1)}_{L_{mu }-{L}_{tau }} , the scalar leptoquark S3, and the vector leptoquark U1. We find that a 3 TeV MuC has a sensitivity reach comparable to the one of the FCC-hh. However, for a heavy enough mediator, the new physics effects at a 3 TeV MuC are only observed indirectly via deviations in the highest energy bin, while the FCC-hh has a greater potential for the discovery of a resonance. Finally, to completely cover the parameter space suggested by the bsμμ anomalies, among the proposed future colliders, only a MuC of 10 TeV (or higher) can meet the challenge.

Deviations from tribimaximal and golden ratio mixings under radiative corrections of neutrino masses and mixings

The impact of renormalization group equations on neutrino masses and mixings at high-energy scales in the Minimal Supersymmetric Standard Model is studied using two different mixing patterns such as Tribimaximal (TBM) mixing and Golden Ratio (GR) mixing in consistent with cosmological bound of the sum of three neutrino masses, [Formula: see text]. Magnifications of neutrino masses and mixing angles at low-energy scales are obtained by giving proper input masses, and mixing angles from the TBM mixing matrix and GR mixing matrix at high-energy scales. High-energy scales, [Formula: see text] such as [Formula: see text], [Formula: see text], [Formula: see text] GeV are employed in the analysis. The large solar ([Formula: see text]) and atmospheric ([Formula: see text]) neutrino mixing angles with zero reactor angle ([Formula: see text]) from both TBM mixing matrix and GR mixing matrix at high scale, can magnify the reactor angle ([Formula: see text]) at low-energy scale in 3[Formula: see text] confidence level. Both cases of normal hierarchy and inverted hierarchy are addressed here. In a normal hierarchical case, it is found that [Formula: see text] and that in an inverted hierarchical case is [Formula: see text] in both mixing patterns. Possibility of [Formula: see text] or [Formula: see text] is observed at low scale. The analysis shows the validity of the two mixing patterns at a high-energy scale.

Probing Leptogenesis with the Cosmological Collider.

Leptogenesis is generally challenging to directly test due to the very high energy scales involved. In this Letter, we propose a new probe for leptogenesis with cosmological collider physics. With the example of a cosmological Higgs collider, we demonstrate that during inflation leptogenesis models can produce detectable primordial non-Gaussianity with distinctive oscillatory patterns that encode information about the lepton-number violating couplings, the Majorana right-hand neutrino masses, and the CP phases, which are essential to leptogenesis.

Boosted Tau Lepton as a Microscope and Macroscope

Anomalies from the LHCb lepton flavour universality and Fermilab muon anomalous magnetic moment show tantalizing hints of possible new physics from the lepton sectors. Due to its large mass and shorter lifetime than muon, the tau lepton is believed to couple more to possible new physics beyond the Standard Model. Traditionally, tau leptons are probed through their decay products due to tau’s short lifetime. On the other hand, at a high energy scale, a large fraction of tau leptons could be boosted to a much longer lifetime and fly a visible distance from several centimetres up to kilometer length scale yet very informative to new physics beyond the standard model or high energy cosmic rays. In this article, we investigate rare, yet promising, tau-physics phenomena, where long-lived taus are exploited either as a microscope (for the measurement of tau’s anomalous magnetic moment to an unprecedented level of accuracy) or as a macroscope (for the detection of 1 TeV to 1 PeV cosmic neutrinos).

Fermiophobic light Higgs boson in the type-I two-Higgs-doublet model

The null results in the new physics searches at the LHC do not exclude a light new particle if the particle is fermiophobic. A good example is the fermiophobic Higgs boson hf in the type-I two-Higgs-doublet model, which occurs if we adopt α=π/2 and the inverted scenario where the heavier CP-even Higgs boson is the observed one at a mass of 125 GeV. We first obtain the still-valid parameter space satisfying the theoretical requirements, flavor-changing neutral currents in B physics, the cutoff scale above 1 TeV, Higgs precision data, and the direct search bounds at high energy colliders. We also study the high energy scale behavior of the allowed parameter points via the renormalization group equation analysis. An important result is that the fermiophobic type-I can maintain the stability of the scalar potential all the way up to the Planck scale if mhf is larger than half the observed Higgs boson mass. Since the decay modes of hf→γγ, H±→hfW±, and A→hfZ are dominant, the productions of pp→Ahf/H±hf/H±A/H+H− yield the four-photon final states at the LHC. We suggest the processes of 4γ+VV′ (V(′)=Z,W±) as the discovery channels that supplement 4γ+V, since they have compatible cross sections and enjoy the background-free environment.

Implications of a holographic density of states on inflation

There is theoretical evidence that the number of degrees of freedom in quantum fields decreases as one studies them at extremely short distances. This emerges from the study of entropy of black holes, as well as from holographic theories in AdS geometries. Presumably a theory of quantum gravity will provide an explicit description of how the number of degrees of freedom thin out as one studies high energy scales. We do not have a comprehensive theory of how such a thinning of degrees of freedom would occur. It is likely that there might be residual (and measurable) effects at larger length scales, though this might be significant only near the Planck scale. There are very few instances in Nature where one might be able to see effects of this thinning. One promising venue is in the phenomenon of inflation, produced in the simplest models through a scalar inflaton field in a potential with a flat (“slow-roll”) part as well as a potential well. During inflation, fluctuations of small length scales are stretched to large scales and then exit the Hubble horizon. We compute the effect of such a thinning of degrees of freedom upon the running of the spectral index of quantum fluctuations of the inflaton and deduce that this will lead to a small positive power of wave vector (opposite to the usual , i.e., negative power correction). Some comments are then made about the impact on observations (or non-observations) of such fluctuations (Martin J. and Ringeval C., Phys. Rev. D, 69 (2004) 083515).

Searches for Heavy Resonances with Substructure

In the past decade, the Large Hadron Collider (LHC) has probed a higher energy scale than ever before. Most models of physics beyond the standard model (BSM) predict the production of new heavy particles; the LHC results have excluded lower masses of such particles. This makes the high-mass regions especially interesting for current and future searches. In most BSM scenarios of interest, the new heavy resonances decay to standard model particles. In a subset of these models, the new particles have large couplings to the top quark, the W and Z bosons, or the Higgs boson. The top quark and W, Z, and Higgs bosons often decay to quarks, giving rise to jets of particles with substructure; event selection based on substructure is used to suppress standard model backgrounds. This review covers the key concepts in experimental searches based on the jet substructure and discusses recent results from the ATLAS and CMS experiments.

Gauge enhanced quantum criticality beyond the standard model

Standard lore ritualizes our quantum vacuum in the four-dimensional spacetime (4D) governed by one of the candidate Standard Models (SMs), while lifting towards some grand unification-like structure (GUT) at higher energy scales. In contrast, in our work, we introduce an alternative view that the SM is a low energy quantum vacuum arising from various neighbor vacua competition in an immense quantum phase diagram. In general, we can regard the SM arising near the gapless quantum criticality (either critical points or critical regions) between the competing neighbor vacua. In particular detail, we demonstrate how the $su(3)\ifmmode\times\else\texttimes\fi{}su(2)\ifmmode\times\else\texttimes\fi{}u(1)$ SM with 16n Weyl fermions arises near the quantum criticality between the GUT competition of Georgi-Glashow $su(5)$ and Pati-Salam $su(4)\ifmmode\times\else\texttimes\fi{}su(2)\ifmmode\times\else\texttimes\fi{}su(2)$. We propose two enveloping toy models. Model I is the conventional $so(10)$ GUT with a Spin(10) gauge group plus GUT-Higgs potential inducing various Higgs transitions. Model II modifies model I by adding a new 4D discrete torsion class of Wess-Zumino-Witten-like term built from GUT-Higgs field [which matches a nonperturbative global mixed gauge-gravity anomaly captured by a 5D invertible topological field theory ${w}_{2}{w}_{3}(TM)={w}_{2}{w}_{3}({V}_{\mathrm{SO}(10)})$], which manifests a beyond-Landau-Ginzburg quantum criticality between Georgi-Glashow and Pati-Salam models, with extra beyond the Standard Model excitations emerging near a hypothetical quantum critical region. If the internal symmetries were treated as global symmetries (or weakly coupled to probe background fields), we suggest a particular low-energy realization of model II as an analogous gapless 4D deconfined quantum criticality with new beyond the SM fractionalized fragmentary excitations of color-flavor separation, and gauge enhancement including a dark gauge force sector, altogether requiring a double fermionic Spin structure named DSpin. If the internal symmetries are dynamically gauged (as they are in our quantum vacuum), we suggest the model II's 4D criticality as a boundary criticality such that only appropriately gauge enhanced dynamical GUT gauge fields can propagate into an extradimensional 5D bulk. The phenomena may be regarded as SM deformation or ``morphogenesis.'' Although our derivation is based on kinematics and global anomaly matching constraints between UV parent and various candidate IR field theories, the constraints are still highly subtle and suggestive. Future verifications on the IR dynamics will be desirable.

Doubly peaked induced stochastic gravitational wave background: testing baryogenesis from primordial black holes

Hawking evaporation of primordial black holes (PBHs) can facilitate the generation of matter-antimatter asymmetry. We focus on ultra-low mass PBHs that briefly dominate the universe and evaporate before the big bang nucleosynthesis. We propose a novel test of this scenario by detecting its characteristic doubly peaked gravitational wave (GW) spectrum in future GW observatories. Here the first order adiabatic perturbation from inflation and from the isocurvature perturbations due to PBH distribution, source tensor perturbations in second-order and lead to two peaks in the induced GW background. These resonant peaks are generated at the beginning of standard radiation domination in the presence of a prior PBH-dominated era. This unique GW spectral shape would provide a smoking gun signal of non-thermal baryogenesis from evaporating PBHs, which is otherwise impossible to test in laboratory experiments due to the very high energy scales involved or the feeble interaction of the dark sector with the visible sector.

Traversable wormhole on the brane with non-exotic matter: a broader view

In this article, the possibility of construction of a traversable wormhole on the Randall–Sundrum braneworld with non-exotic matter employing the Kuchowicz potential has been studied. We have obtained the solution for the shape function of the wormhole and studied its properties along with validity of null energy condition. The junction conditions at the surface of the wormhole are used to evaluate the model parameters. We also evaluate the surface density and surface pressure for the wormhole. We study the geometrical nature of the wormhole and consider the radial and tangential tidal constraints on a traveller trying to traverse the wormhole. Besides, a linearized stability analysis is performed to obtain the region of stability for the wormhole. Our analysis, besides giving an estimate for the bulk equation of state (EoS) parameter, imposes restrictions on the brane tension, which is a very essential parameter in braneworld physics, and very interestingly the restrictions imposed by our physically plausible and traversable wormhole model are in conformity with those imposed by other braneworld geometries which are not associated with a wormhole solution. Besides, it is important to study such constraints imposed by geometrical objects such as wormholes on any gravity theory operating at high-energy scales like braneworld, as wormholes are believed to have been formed from massive compact objects of high energy densities. Also, we go on to justify that the possible detection of a wormhole may well indicate that we live on a three-brane universe.

Optical Fingerprints of Nematicity in Iron-Based Superconductors

Nematicity, which refers to a phase of broken rotational but preserved translational symmetry, is underlined by the appearance of anisotropic properties and leaves remarkable fingerprints in all measurable physical quantities upon crossing the structural tetragonal-orthorhombic transition at Ts in several iron-based materials. Here, we review part of our own broadband optical investigations, addressing the impact of nematicity on the charge dynamics, as a function of temperature and of tunable applied stress, the latter acting as an external symmetry breaking field. We shall first focus our attention on FeSe, which undergoes a nematic (structural) transition without any subsequent onset of magnetic ordering below Ts. FeSe thus provides an opportunity to study nematicity without the limitations due to the reconstruction of the Fermi surface because of the spin-density-wave collective state in the orthorhombic phase, typical for several other iron-based superconductors. Our data reveal an astonishing anisotropy of the optical response in the mid-infrared-to-visible spectral range, which bears testimony of an important polarization of the underlying electronic structure in agreement with angle-resolved-photoemission-spectroscopy results. Our findings at high energy scales support models for the nematic phase resting on an orbital-ordering mechanism, supplemented by orbital selective band renormalization. The optical results at energies close to the Fermi level furthermore emphasize scenarios relying on scattering by anisotropic spin-fluctuations and shed new light on the origin of nematicity in FeSe. Moreover, the composition at which the associated Weiss temperature of the nematic susceptibility extrapolates to zero is found to be close to optimal doping (i.e., in coincidence with the largest superconducting transition temperature), boosting the debate to what extent nematic fluctuations contribute to the pairing-mechanism and generally affect the electronic structure of iron-based superconductors. The present review then offers a discussion of our optical data on the optimally hole-doped Ba0.6K0.4Fe2As2. We show that the stress-induced optical anisotropy in the infrared spectral range is reversible upon sweeping the applied stress and occurs only below the superconducting transition temperature. These findings demonstrate that there is a large electronic nematicity at optimal doping which extends right under the superconducting dome.

Ultraviolet properties of Lifshitz-type scalar field theories

We consider Lifshitz-type scalar field theories that exhibit anisotropic scaling laws near the ultraviolet fixed point, with explicit breaking of Lorentz symmetry. It is shown that, when all momentum dependent vertex operators are discarded, actions with anisotropy parameter z=3 in 3+1 dimensions generate Lorentz symmetry violating quantum corrections that are suppressed by inverse powers of the momentum, so that the symmetry is sensibly restored in the infrared region. In the ultraviolet region, the singular behavior of the corrections is strongly smoothened: only logarithmic divergences show up, producing very small changes of the couplings over a range of momentum of many orders of magnitude. In the particular case where all couplings are equal, the theory shows a Liouville-like potential and quantum corrections are exactly summable, giving an asymptotically free theory. However, the observed weakening of the divergences is not sufficient to avoid a residual fine tuning of the mass parameter at a very high energy scale, in order to recover a physically acceptable mass in the infrared region.

Axion isocurvature collider

Cosmological colliders can preserve information from interactions at very high energy scale, and imprint them on cosmological observables. Taking the squeezed limit of cosmological perturbation bispectrum, information of the intermediate particle can be directly extracted from observations such as cosmological microwave background (CMB). Thus cosmological colliders can be powerful and promising tools to test theoretical models. In this paper, we study extremely light axions (including QCD axions and axion-like-particles), and consider them constituting cold dark matter (CDM) at late times. We are interested in inflationary isocurvature modes by such axions, and try to figure out how axion perturbations can behave as isocurvature colliders. We work out an example where the intermediate particle is a boson, and show that, in the squeezed limit, it is possible to provide a clock signal of significant amplitudes, with a characteristic angular dependence. This provides a channel to contribute and analyze clock signals of isocurvature bispectrum, which we may hopefully see in future experiments.

Probing new physics at future tau neutrino telescopes

We systematically investigate new physics scenarios that can modify the interactions between neutrinos and matter at upcoming tau neutrino telescopes, which will test neutrino-proton collisions with energies ≳ 45 TeV, and can provide unique insights to the elusive tau neutrino. At such high energy scales, the impact of parton distribution functions of second and third generations of quarks (usually suppressed) can be comparable to the contribution of first generation with small momentum fraction, hence making tau neutrino telescopes an excellent facility to probe new physics associated with second and third families. Among an inclusive set of particle physics models, we identify new physics scenarios at tree level that can give competitive contributions to the neutrino cross sections while staying within laboratory constraints: charged/neutral Higgs and leptoquarks. Our analysis is close to the actual experimental configurations of the telescopes, and we perform a χ2-analysis on the energy and angular distributions of the tau events. By numerically solving the propagation equations of neutrino and tau fluxes in matter, we obtain the sensitivities of representative upcoming tau neutrino telescopes, GRAND, POEMMA and Trinity, to the charged Higgs and leptoquark models. While each of the experiments can achieve a sensitivity better than the current collider reaches for certain models, their combination is remarkably complementary in probing the new physics. In particular, the new physics will affect the energy and angular distributions in different ways at those telescopes.

About the Power Spectrum Of Primordial Gravitational Waves

The primordial gravitational waves (PGW) have been generated by inflationary amplification of the primordial (quantum) fluctuations. It is true that they have not been recorded directly so far, but their spectrum can help a lot in solving the basic puzzles of the early universe as Inflation (high) energy scale. In the present work, we give a straightforward method to calculate the spectral energy density (SED) of the relic gravitons different from that used in e.g. Jinno et al. JCAP 1, 41 (2014), Boyle and Steinhardt, Phys. Rev. D 77, 063504 (2008) and Watanabe and Komatsu, Phys. Rev. D 73, 123515 (2006). In our approach, the evolution equations are in terms of the scale factor (instead of conformal time) through the Lagrange formalism (instead of the transfer function). The presence of the Hubble parameter allows to calculate the power spectrum in the different dynamical regimes.

Effect of (Na, Si, Al, K or Ca) doping on the electronic structure and optoelectronic properties of half-Heusler LiMgN alloy: Ab initio framework

The effect of (YNa, Si, Al, K or Ca)- dopant have been investigated on the electronic structure and optoelectronic properties of LiMgN. In the present work, the ab initio is carried out within the full-potential linearized augmented plane wave (FP—LAPW) framework. The generalized gradient approximation with the modified Becke—Johnson potential approximation (TB-mBJ) proposed by Tran and Blaha is applied to LiMgN, in which the Mg is being substituted by an amount of 6.25% of (Na-, Si-, Al-, K-, or Ca-). The results show that the undoped LiMgN has a band gap of 3.954 eV. Where the band structure and density of states (DOS) analysis exhibit the n-type conductivity when (YSi or Al) and the p-type conductivity is predicted when (YNa, K or Ca). The imaginary part of dielectric function ε2(ω) has been plotted, in which the peaks of (Na, K and Ca) shift to the high energy scale thanks to the holes originating from these elements. Also, the absorption coefficient α(ω) and reflectivity R(ω) are plotted. The α(ω) of Si is higher than the others, a peak appeared at around 350 nm in blue-shift. The α(ω) of Ca is close to the pure one, from which the Ca doped LiMgN can be considered as transparent material in the visible range. Where the R(ω) of pure LiMgN and Ca-doped LiMgN alloys is of 10% in the visible range.

Are low-energy data already hinting at five dimensions?

Low-energy data, combined with renormalization group (RG) equations, can predict new physics at far higher energy scales. In this paper, we consider the possibility that the measured Higgs boson mass and top quark mass hint at a five-dimensional gauge-Higgs unification (5D GHU) model at a scale above TeV. We note that the vanishing of the Higgs quartic coupling and the proximity of the top quark Yukawa coupling and weak gauge coupling at high scales, inferred from the experimental data, are in harmony with 5D GHU, because in 5D GHU models the Higgs quartic coupling is forbidden by the 5D gauge symmetry and the Yukawa couplings and the weak gauge coupling originate from a common 5D gauge coupling. Based on the above insight, we propose a 5D GHU model where the Standard Model fermions are embedded in 5D fermions in a way to tightly relate the top Yukawa coupling with the weak gauge coupling. Also, the model predicts the presence of vector-like fermions (other than the Kaluza-Klein modes), which can affect the RG evolutions of the 4D theory and reconcile the scale of vanishing Higgs quartic coupling and that of equality of the top Yukawa and weak gauge couplings, thereby achieving a successful matching of the 4D theory with 5D GHU. We predict the vector-like fermion mass and the compactification scale of 5D GHU from the conditions for the successful matching.

Gravitational waves from melting cosmic strings

Appearance of cosmic strings in the early Universe is a common manifestation of new physics typically linked to some high energy scale. In this paper, we discuss a different situation, where a model underlying cosmic string formation is approximately scale free. String tension is naturally related to the square of the temperature of the hot primordial plasma in such a setting, and hence decreases with (cosmic) time. With gravitational backreaction neglected, the dynamicsof these melting strings in an expanding Universe is equivalent to the dynamics of constant tension strings in a Minkowski spacetime.We provide an estimate for the emission of gravitational waves from string loops. Contrary to the standard case, the resulting spectrum is markedly non-flat and has a characteristic falloffat frequencies below the peak one. The peak frequency is defined by the underlying model and lies in the range accessible by the future detectors for very weak couplings involved.