Scale Invariant Sector Research Articles

Unparticle decay of neutrinos and its possible signatures at Km2 detector for (3+1) flavour framework

We consider a scenario where ultra high energy neutrinos undergo unparticle decay during its passage from its cosmological source to Earth. The idea of unparticle had been first proposed by Georgi by considering the possible existence of an unknown scale invariant sector at high energies and the unparticles in this sector manifest itself below a dimensional transmutation scale {Lambda}_{mathcal{U}} . We then explore the possible signature of such decaying neutrinos to unparticles at a square kilometer detector such as IceCube.

Scale invariance as the cause of the superconducting dome in the cuprates

Recent photoemission spectroscopy measurements (T. J. Reber et al., arXiv:1509.01611) of cuprate superconductors have inferred that the self-energy exhibits critical scaling over an extended doping regime, thereby calling into question the conventional wisdom that critical scaling exists only at isolated points. In particular, this new state of matter, dubbed a power-law liquid, has a self-energy whose imaginary part scales as $\Sigma^{\prime\prime}\sim(\omega^{2}+\pi^{2}T^{2})^{\alpha}$, with $\alpha=1$ in the overdoped Fermi-liquid state and $\alpha\leq0.5$ in the optimal to underdoped regime. Previously, we showed that this self-energy can arise from interactions between electrons and unparticles, a scale-invariant sector that naturally emerges from strong correlations. Here, taking the self-energy as a given, we first reconstruct the real part of the self-energy. We find that the resultant quasiparticle weight vanishes for any doping level less than optimal, implying an absence of particle-like excitations in the underdoped regime. Consequently, the Fermi velocity vanishes and the effective mass diverges for $\alpha\leq\frac{1}{2}$, in agreement with earlier experimental observations. We then use the self-energy to reconstruct the spectral function and compute the superconducting $T_c$ within the BCS formalism. We find that the $T_c$ has a dome-like structure, implying that broad scale invariance manifested in the form of a power-law liquid is the likely cause of the superconducting dome in the cuprates.

Unparticle Casimir effect

In this paper we present the un-Casimir effect, namely the study of the Casimir energy in the presence of an unparticle component in addition to the electromagnetic field contribution. The distinctive feature of the un-Casimir effect is a fractalization of metallic plates. This result emerges through a new dependence of the Casimir energy on the plate separation that scales with a continuous power controlled by the unparticle dimension. As long as the perfect conductor approximation is valid, we find bounds on the unparticle scale that are independent of the effective coupling constant between the scale invariant sector and ordinary matter. We find regions of the parameter space such that for plate distances around 5 μm and larger the un-Casimir bound wins over the other bounds.

WIMP miracle of the second kind

We study dark matter production in scenarios where a scale invariant hidden sector interacts with the Standard Model degrees of freedom via a Higgs portal $\lambda \Phi^\dagger\Phi s^2$. If the hidden sector is very weakly coupled to the SM but exhibits strong interactions within its own particle species, the dark matter abundance may arise as a result of a dark freeze-out occurring in the hidden sector. Because of scale invariance, the free parameters in the hidden sector are determined and the dark matter candidate exhibits a 'WIMP miracle of the second kind'. Demonstrating the predictive power of scale invariance, we carry out thorough analysis of dark matter production in several benchmark scenarios where the hidden sector contains either a scalar, fermion (sterile neutrino), or vector dark matter, and discuss the observational consequences of these scenarios.

Realizing infrared power-law liquids in the cuprates from unparticle interactions

Recent photoemission experiments [1] reveal that the excitations along the nodal region in the strange metal phase of the cuprates, rather than corresponding to poles in the single-particle Green function, exhibit power-law scaling as a function of frequency and temperature. Because such power-law scaling is indicative of a scale-invariant sector, as a first step, we perturbatively evaluate the electron self-energy due to interactions with scale-invariant unparticles. We focus on a ${G}_{0}W$-type diagram with an interaction $W$ mediated by a bosonic scalar unparticle. We find that in the high-temperature limit, the imaginary part of the self-energy $\mathrm{Im}\mathrm{\ensuremath{\Sigma}}$ is linear in temperature. In the low-temperature limit, $\mathrm{Im}\mathrm{\ensuremath{\Sigma}}$ exhibits the same power law in both temperature and frequency, with an exponent that depends on the scaling dimension of an unparticle operator. Such behavior is qualitatively consistent with the experimental observations. We then expand the unparticle propagator into coherent and incoherent contributions and study how the incoherent part violates the density of states (DOS) and density-density correlation function sum rules (f-sum rule). Such violations, in principle, can be observed experimentally. Our work indicates that the physical mechanism for the origin of the power-law scaling is the incoherent background, which is generated from the Mott-scale physics.

Unparticle effects in neutrino telescopes

Recently H. Georgi has introduced the concept of unparticles in order to describe the low energy physics of a nontrivial scale invariant sector of an effective theory. We investigate its physical effects on the neutrino flux to be detected in a kilometer cubic neutrino telescope such as IceCube. We study the effects, on different observables, of the survival neutrino flux after through the Earth, and the regeneration originated in the neutral currents. We calculate the contribution of unparticle physics to the neutrino-nucleon interaction and, then, to the observables in order to evaluate detectable effects in IceCUbe. Our results are compared with the bounds obtained by other nonunderground experiments. Finally, the results are presented as an exclusion plot in the relevant parameters of the new physics stuff.

TOP OFF THE UNPARTICLE

The existence of an exactly scale invariant sector possessing a nontrivial infrared fixed point at a higher energy scale and its possible communication with the Standard Model particles through a heavy messenger sector has been shown to lead to curious unparticle effects. We demonstrate that top physics at the Tevatron can already constrain such theories. We also consider possible improvements at the LHC and delineate some striking signatures.

THERMAL PROPERTIES OF UNPARTICLE

We report the study1 on the thermal properties of unparticle, a scale invariant sector with a non-trivial infrared fixed point. Unparticle [Formula: see text] with scaling dimension [Formula: see text] has peculiar thermal properties due to its unique phase space structure. We find that the equation of state parameter [Formula: see text], the ratio of pressure to energy density, is given by [Formula: see text] providing a new form of energy in our universe. In an expanding universe, the unparticle energy density [Formula: see text] evolves dramatically differently from that for photons, which makes it possible to have a large unparticle relic density today.

W-pair production in unparticle physics

We consider the W-pair production for both e+e− and hadron colliders in the context of unparticle physics associated with the scale invariant sector proposed by Georgi. We have shown that the unparticle contributions are quite comparable with Standard Model (SM) specially for low values of non-integral scaling dimension (dU) and hence it is worthwhile to explore in current and future colliders.

Disentangling the unparticles with polarized beams ate+e−colliders

A recently proposed idea of unparticles arising due to a scale invariant sector in the theory can give rise to effective operators with different Lorentz structures. We show that, by using the different polarization options at the future linear ${e}^{+}{e}^{\ensuremath{-}}$ colliders, the nature of these effective operators can be easily understood. The unique feature of a complex phase in the propagator of the unparticle can also be understood distinctively for the different spins by exploiting the initial beam polarizations at the International Linear Collider.

Unparticles at heavy flavor scales:CPviolating phenomena

Coupling the scale invariant unparticle sector to flavor physics and assuming that it remains scale invariant I investigate its consequences in heavy flavor physics. A characteristic feature of unparticle physics is a $CP$-even phase leading to novel $CP$ violating phenomena. The phase is large, based on the assumption that the unparticle sector is strongly self-coupled. I consider the $CP$ asymmetry in the leptonic decay ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}\ensuremath{\nu}$ and the hadronic decay ${B}_{d}\ensuremath{\rightarrow}{D}^{+}{D}^{\ensuremath{-}}$, taking into account constraints of branching ratios and time dependent $CP$ asymmetries. It turns out that the $CP$ asymmetry can be very large even for small couplings because the unparticle interaction term has a lower scaling dimension than the four-Fermi weak interaction term. $CP$ asymmetries in leptonic decays such as ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}\ensuremath{\nu}$ are neither experimentally searched for nor predicted by any other model. I show that the novel $CP$ violation is consistent with the $CPT$ theorem. I identify the $CP$ compensating mode in the unparticle sector and explicitly demonstrate the exact cancellation as demanded by the $CPT$ theorem.

Scalar Modifications to Gravity from Unparticle Effects May Be Testable

Interest has focused recently on low energy implications of a nontrivial scale invariant sector of an effective field theory with an IR fixed point, manifest in terms of "unparticles" with peculiar properties. If unparticle stuff exists it could couple to the stress tensor and mediate a new "fifth" force ("ungravity"). Under the assumption of strict conformal invariance in the hidden sector down to low energies, we compute the lowest order ungravity correction to the Newtonian gravitational potential and find scale invariant power law corrections of type (R_(G)/r)(2d)_(U)(-1), where d_(U) is an anomalous unparticle dimension and R_(G) is a characteristic length scale where the ungravity interactions become significant. It is shown that a discrimination between extra dimension models and ungravity is possible in future improved submillimeter tests of gravity.

Long range forces and limits on unparticle interactions

Couplings between standard model particles and unparticles from a nontrivial scale invariant sector can lead to long range forces. If the forces couple to quantities such as baryon or lepton (electron) number, stringent limits result from tests of the gravitational inverse square law. These limits are much stronger than from collider phenomenology and astrophysics.

Interactions of unparticles with standard model particles

We study interactions of unparticles $\mathcal{U}$ of dimension ${d}_{\mathcal{U}}$ due to Georgi with standard model (SM) fields through effective operators. The unparticles describe the low energy physics of a nontrivial scale invariant sector. Since unparticles come from beyond the SM physics, it is plausible that they transform as a singlet under the SM gauge group. This helps tremendously in limiting possible interactions. We analyze interactions of scalar $\mathcal{U}$, vector ${\mathcal{U}}^{\ensuremath{\mu}}$, and spinor ${\mathcal{U}}^{s}$ unparticles with SM fields and derivatives up to dimension four. Using these operators, we discuss different features of producing unparticles at an ${e}^{+}{e}^{\ensuremath{-}}$ collider and other phenomenologies. It is possible to distinguish different unparticles produced at an ${e}^{+}{e}^{\ensuremath{-}}$ collider by looking at various distributions of production cross sections.

Lepton flavour violation in unparticle physics

Recently H. Georgi has introduced an unparticle U in order to describe the low energy physics of a nontrivial scale invariant sector of an effective theory. In this work we have explored the phenomenology of an unparticle using the lepton flavour violating decay μ−→e−e+e−, and found that the branching ratio of this decay is strongly dependent on the scaling dimension.

Collider phenomenology of unparticle physics

Low-energy phenomenology of the unparticle physics associated with an exact scale invariant sector possessing a nontrivial infrared fixed point at a higher energy scale is explored for both electron-positron and hadronic colliders. Feynman rules for a spin 0, 1, or 2 unparticle coupled to a variety of standard model gauge invariant operators that are relevant to many low-energy processes involving either real emissions of unparticles or their virtual propagator effects are presented. Missing energy and/or recoil mass distributions of the unparticle in the associated production of the unparticle together with a photon or Z boson at LEP2 and ILC as well as in Z decay into an unparticle plus a fermion-antifermion pair are studied. In addition, monojet production with missing energy from the unparticle at hadronic collisions are explored. The complex phase in the unparticle propagator that can give rise to interesting interference effects between an unparticle-exchange diagram and the standard model amplitudes are studied in details for the Drell-Yan process as well as muon pair and diphoton production in electron-positron annihilation. These energy and/or recoil mass distributions (with the exception in hadron colliders) and interference effects are found sensitively depending not only on the scaling dimension but also onmore » the spin of the unparticle. For the spin-2 unparticle, its physical effects are found to resemble that of a tower of Kaluza-Klein gravitons, which strongly indicates that the underlying unparticle physics may have root in a higher dimensional theory. A connection between unparticle physics and theories of large extra dimensions is speculated. Experimental constraints on the unparticle scale are deduced from the LEP2 data on monophoton production and from the 4-fermion contact interactions.« less

Collider Signals of Unparticle Physics

Phenomenology of the notion of an unparticle U, recently perceived by Georgi, to describe a scale invariant sector with a nontrivial infrared fixed point at a higher energy scale is explored in details. Behaving like a collection of d(U) (the scale dimension of the unparticle operator O(U)) invisible massless particles, this unparticle can be unveiled by measurements of various energy distributions for the processes Z-->f f U and e- e+-->gammaU at e- e+ colliders, as well as monojet production at hadron colliders. We also study the propagator effects of the unparticle through the Drell-Yan tree-level process and the one-loop muon anomaly.

Unparticle Physics

I discuss some simple aspects of the low-energy physics of a nontrivial scale invariant sector of an effective field theory-physics that cannot be described in terms of particles. I argue that it is important to take seriously the possibility that the unparticle stuff described by such a theory might actually exist in our world. I suggest a scenario in which some details of the production of unparticle stuff can be calculated. I find that in the appropriate low-energy limit, unparticle stuff with scale dimension dU looks like a nonintegral number dU of invisible particles. Thus dramatic evidence for a nontrivial scale invariant sector could show up experimentally in missing energy distributions.

Exact Results for Supersymmetric Renormalization and the Supersymmetric Flavor Problem

We explore the effects of a strongly-coupled, approximately scale-invariant sector on the renormalization of soft supersymmetry breaking terms. A useful formalism for deriving exact results for renormalization of soft supersymmetry breaking terms is given in an appendix, and used to generalize previously known results to include the effects of nontrilinear superpotential terms. We show that a class of theories which explain the flavor hierarchy without flavor symmetries can also solve the supersymmetric flavor problem by producing nearly degenerate masses for the first two generations of scalar superpartners within each charge sector. Effects from trilinear scalar terms are also suppressed, although their initial values must be relatively small. Our mechanism results in testable predictions for the superpartner spectrum.