Short-distance Physics Research Articles

Extended model for monopole catalysis of nucleon decay

A new model for monopole catalysis of nucleon decay is proposed. Unlike in the earlier one, the only light fields in this model are the photon and Skyrme (pion) field. The model admits the 't Hooft--Polyakov monopole and Skyrmion as classical solutions, while baryon number nonconservation occurs through an anomaly involving an intermediate mass axial vector field resembling W and Z bosons. By considering spherically symmetric monopole-Skyrmion configurations, we find that the Skyrmion loses essentially all its mass when interacting with the monopole, which is phenomenologically identical to the monopole catalysis of nucleon decay. Short-distance monopole-Skyrmion physics in this model is interesting too, as there exist almost degenerate metastable monopole-Skyrmion bound states separated by substantial energy barriers. Yet the height of the latter is much smaller than the physical nucleon mass, so the complete disappearance of the normal undeformed Skyrmion remains perfectly possible in Skyrmion-monopole scattering.

Signatures of short distance physics in the cosmic microwave background

We systematically investigate the effect of short distance physics on the spectrum of temperature anistropies in the Cosmic Microwave Background produced during inflation. We present a general argument-assuming only low energy locality-that the size of such effects are of order H^2/M^2, where H is the Hubble parameter during inflation, and M is the scale of the high energy physics. We evaluate the strength of such effects in a number of specific string and M theory models. In weakly coupled field theory and string theory models, the effects are far too small to be observed. In phenomenologically attractive Horava-Witten compactifications, the effects are much larger but still unobservable. In certain M theory models, for which the fundamental Planck scale is several orders of magnitude below the conventional scale of grand unification, the effects may be on the threshold of detectability. However, observations of both the scalar and tensor fluctuation contributions to the Cosmic Microwave Background power spectrum-with a precision near the cosmic variance limit-are necessary in order to unambiguously demonstrate the existence of these signatures of high energy physics. This is a formidable experimental challenge.

Lepton pair decays of theKLmeson in the light-front model

We analyze $K_L$ lepton pair decays of $K_L \to l^+\l^-\gamma$ and $K_L \to l^+l^-l'^+l'^-$ $(l, l'=e, \mu)$ within the framework of the light-front QCD approach (LFQA). With the $K_L \to \gamma^* \gamma^*$ form factors evaluated in a model with the LFQA, we calculate the decay branching ratios and find out that our results are all consistent with the experimental data. In addition, we study $K_L \to l^+l^-$ decays. We point out that our prediction on $K_L\to e^+e^-$ is about 20% smaller than that in the ChPT. We also discuss whether one could extract the short-distance physics from $K_L\to \mu^+\mu^-$.

Rare charm decays in the standard model and beyond

We perform a comprehensive study of a number of rare charm decays, incorporating the first evaluation of the QCD corrections to the short distance contributions, as well as examining the long range effects. For processes mediated by the c → ul + l − transitions, we show that sensitivity to short distance physics exists in kinematic regions away from the vector meson resonances that dominate the total rate. In particular, we find that D → πl + l − and D → ρl + l − are sensitive to non-universal soft-breaking effects in the Minimal Supersymmetric Standard Model with R-parity conservation. We separately study the sensitivity of these modes to R-parity violating effects and derive new bounds on R-parity violating couplings. We also obtain predictions for these decays within extensions of the Standard Model, including extensions of the Higgs, gauge and fermion sectors, as well as models of dynamical electroweak symmetry breaking.

Short distance versus long distance physics: The classical limit of the minimal length uncertainty relation

We continue our investigation of the phenomenological implications of the ``deformed'' commutation relations $[{x}_{i},{p}_{j}]=i\ensuremath{\Elzxh}[(1+\ensuremath{\beta}{p}^{2}){\ensuremath{\delta}}_{\mathrm{ij}}+{\ensuremath{\beta}}^{\ensuremath{'}}{p}_{i}{p}_{j}].$ These commutation relations are motivated by the fact that they lead to the minimal length uncertainty relation which appears in perturbative string theory. In this paper, we consider the effects of the deformation on the classical orbits of particles in a central force potential. Comparison with observation places severe constraints on the value of the minimum length.

Cosmological perturbations and short distance physics from Noncommutative Geometry

We investigate the possible effects on the evolution of perturbations in the inflationary epoch due to short distance physics. We introduce a suitable non local action for the inflaton field, suggested by Noncommutative Geometry, and obtained by adopting a generalized star product on a Friedmann-Robertson-Walker background. In particular, we study how the presence of a length scale where spacetime becomes noncommutative affects the gaussianity and isotropy properties of fluctuations, and the corresponding effects on the Cosmic Microwave Background spectrum.

On the signature of short distance scale in the cosmic microwave background

We discuss the signature of the scale of short distance physics in the Cosmic Microwave Background. In addition to effects which depend on the ratio of Hubble scale H during inflation to the energy scale M of the short distance physics, there can be effects which depend on φ ̇ 2/M 4 where φ is the classical background of the inflaton field. Therefore, the imprints of short distance physics on the spectrum of Cosmic Microwave Background anisotropies generically involve a double expansion. We present some examples of a single scalar field with higher order kinetic terms coupled to Einstein gravity, and illustrate that the effects of short distance physics on the Cosmic Microwave Background can be substantial even for H⪡ M, and generically involve corrections that are not simply powers of H/ M. The size of such effects can depend on the short distance scale non-analytically even though the action is local.

Short distance physics and the consistency relation for scalar and tensor fluctuations in the inflationary universe

Recent discussions suggest the possibility that short distance physics can significantly modify the behavior of quantum fluctuations in the inflationary universe, and alter the standard large scale structure predictions. Such modifications can be viewed as due to a different choice of the vacuum state. We show that such changes generally lead to violations of the well-known consistency relation between the scalar to tensor ratio and the tensor spectral index. Vacuum effects can introduce an observable modulation to the usual predictions for the scalar and tensor power spectra.

Short distance physics with heavy quark potentials

We present lattice studies of heavy quark potentials in the quenched approximation of QCD at finite temperatures. Both, the color singlet and color averaged potentials are calculated. While the potentials are well known at large distances, we give a detailed analysis of their short distance behavior (from 0.015 fm to 1 fm) near the critical temperature. At these distances we expect that the T-dependent potentials go over into the zero temperature potential. Indeed, we find evidences that the temperature influence gets suppressed and the potentials starts to become a unique function of the underlying distance scale. We use this feature to normalize the heavy quark potentials at short distances and extract the free energy of the quark system in a gluonic heat bath.

High energy colliders as black hole factories: The end of short distance physics

If the fundamental Planck scale is of order a TeV, as the case in some extra-dimensions scenarios, future hadron colliders such as the Large Hadron Collider will be black hole factories. The non-perturbative process of black hole formation and decay by Hawking evaporation gives rise to spectacular events with up to many dozens of relatively hard jets and leptons, with a characteristic ratio of hadronic to leptonic activity of roughly 5:1. The total transverse energy of such events is typically a sizeable fraction of the beam energy. Perturbative hard scattering processes at energies well above the Planck scale are cloaked behind a horizon, thus limiting the ability to probe short distances. The high energy black hole cross section grows with energy at a rate determined by the dimensionality and geometry of the extra dimensions. This dependence therefore probes the extra dimensions at distances larger than the Planck scale.

EINSTEIN GRAVITY AS AN EMERGENT PHENOMENON?

In this essay we marshal evidence suggesting that Einstein gravity may be an emergent phenomenon, one that is not "fundamental" but rather is an almost automatic low-energy long-distance consequence of a wide class of theories. Specifically, the emergence of a curved spacetime "effective Lorentzian geometry" is a common generic result of linearizing a classical scalar field theory around some nontrivial background. This explains why so many different "analog models" of general relativity have recently been developed based on condensed matter physics; there is something more fundamental going on. Upon quantizing the linearized fluctuations around this background geometry, the one-loop effective action is guaranteed to contain a term proportional to the Einstein–Hilbert action of general relativity, suggesting that while classical physics is responsible for generating an "effective geometry," quantum physics can be argued to induce an "effective dynamics." This physical picture suggests that Einstein gravity is an emergent low-energy long-distance phenomenon that is insensitive to the details of the high-energy short-distance physics.

Supernova type Ia data and the cosmic microwave background of modified curvature at short and large distances

The SNIa data, although inconclusive, when combined with other observations makes a strong case that our universe is presently dominated by dark energy. We investigate the possibility that large distance modifications of the curvature of the universe would perhaps offer an alternative explanation of the observation. Our calculations indicate that a universe made up of no dark energy but instead, with a modified curvature at large scales, is not scale invariant; therefore quite likely it is ruled out by the CMB observations. The sensitivity of the CMB spectrum is checked for the whole range of mode modifications of large or short distance physics. The spectrum is robust against modifications of short-distance physics and the UV cutoff when the initial state is the adiabatic vacuum, and the inflationary background space is de Sitter space.

Inflation as a probe of short distance physics

We show that a string-inspired Planck scale modification of general relativity can have observable cosmological effects. Specifically, we present a complete analysis of the inflationary perturbation spectrum produced by a phenomenological Lagrangian that has a standard form on large scales but incorporates a string-inspired short distance cutoff, and find a deviation from the standard result. We use the de Sitter calculation as the basis of a qualitative analysis of other inflationary backgrounds, arguing that in these cases the cutoff could have a more pronounced effect, changing the shape of the spectrum. Moreover, the computational approach developed here can be used to provide unambiguous calculations of the perturbation spectrum in other heuristic models that modify trans-Planckian physics and thereby determine their impact on the inflationary perturbation spectrum. Finally, we argue that this model may provide an exception to constraints, recently proposed by Tanaka and Starobinsky, on the ability of Planck-scale physics to modify the cosmological spectrum.

Analogue gravity from field theory normal modes?

We demonstrate that the emergence of a curved spacetime `effectiveLorentzian geometry' is a common and generic result of linearizing aclassical scalar field theory around some non-trivial backgroundconfiguration. This investigation is motivated by considering the largenumber of `analogue models' of general relativity that have recently beendeveloped based on condensed matter physics, and asking whether there issomething more fundamental going on. Indeed, linearization of a classicalfield theory (that is, a field-theoretic`normal-mode analysis') results in fluctuations whose propagation isgoverned by a Lorentzian-signature curved spacetime `effective metric'.In the simple situation considered in this paper (a single classical scalarfield), this procedure results in a unique effective metric, which is quitesufficient for simulating kinematic aspects of general relativity (up toand including Hawking radiation). Upon quantizing the linearizedfluctuations around this background geometry, the one-loop effectiveaction is guaranteed to contain a term proportional to theEinstein-Hilbert action of general relativity, suggesting that whileclassical physics is responsible for generating an `effective geometry',quantum physics can be argued to induce an `effective dynamics'. Thesituation is strongly reminiscent of, though not identical to, Sakharov's`induced-gravity' scenario, and suggests that Einstein gravity is anemergent low-energy long-distance phenomenon that is insensitive to thedetails of the high-energy short-distance physics. (We mean this in thesame sense that hydrodynamics is a long-distance emergent phenomenon,many of whose predictions are insensitive to the short-distance cut-offimplicit in molecular dynamics.)

Towards Abelian-like formulation of the dual gluodynamics

We consider gluodynamics in case when both color and magnetic charges are present. We discuss first short distance physics, where only the fundamental |Q|=1 monopoles introduced via the `t Hooft loop can be considered consistently. We show that at short distances the external monopoles interact as pure Abelian objects. This result can be reproduced by a Zwanziger-type Lagrangian with an Abelian dual gluon. We introduce also an effective dual gluodynamics which might be a valid approximation at distances where the monopoles |Q|=2 can be considered as point-like as well. Assuming the monopole condensation we arrive at a model which is reminiscent in some respect of the Abelian Higgs model but, unlike the latter leaves space for the Casimir scaling.

High energy hadron spin observables

The free energy between a static quark and an antiquark is studied by using the color-singlet Polyakov-line correlation at finite temperature in lattice QCD with 2+1 flavors of improved Wilson quarks. From the simulations on 323 × 12, 10, 8, 6, 4 lattices in the high temperature phase, based on the fixed scale approach, we find that, the heavy-quark free energies at short distance converge to the heavy-quark potential evaluated from the Wilson loop at zero temperature, in accordance with the expected insensitivity of short distance physics to the temperature. At long distance, the heavy-quark free energies approach to twice the single-quark free energies, implying that the interaction between heavy quarks is screened. The Debye screening mass obtained from the long range behavior of the free energy is compared with the results of thermal perturbation theory.

A critical cosmological constant from millimeter extra dimensions

We consider `brane universe' scenarios with standard-model fields localized on a 3-brane in 6 spacetime dimensions. We show that if the spacetime is rotationally symmetric about the brane, local quantities in the bulk are insensitive to the couplings on the brane. This potentially allows compactifications where the effective 4-dimensional cosmological constant is independent of the couplings on the 3-brane. We consider several possible singularity-free compactification mechanisms, and find that they do not maintain this property. We also find solutions with naked spacetime singularities, and we speculate that new short-distance physics can become important near the singularities and allow a compactification with the desired properties. The picture that emerges is that standard-model loop contributions to the effective 4-dimensional cosmological constant can be cut off at distances shorter than the compactification scale. At shorter distance scales, renormalization effects due to standard-model fields renormalize the 3-brane tension, which changes a deficit angle in the transverse space without affecting local quantities in the bulk. For a compactification scale of order 10^{-2} mm, this gives a standard-model contribution to the cosmological constant in the range favored by cosmology.

Dynamical relaxation of theCPphases in next-to-minimal supersymmetry

After promoting the phases of the soft masses to dynamical fields corresponding to Goldstone bosons of spontaneously broken global symmetries in the supersymmetry breaking sector, the next-to-minimal supersymmetric model is found to solve the $\mu$ problem and the strong CP problem simultaneously with an invisible axion. The domain wall problem persists in the form of axionic domain formation. Relaxation dynamics of the physical CP-violating phases is determined only by the short-distance physics and their relaxation values are not necessarily close to the CP-conserving points. Having observable supersymmetric CP violation and avoiding the axionic domain walls both require nonminimal flavor structures.

Elastic and inelastic neutrino–deuteron scattering in effective field theory

The differential cross-sections for elastic and inelastic neutrino–deuteron scattering are calculated analytically using nucleon–nucleon effective field theory. For elastic scattering, the deuteron axial form factor and the deuteron strange magnetic moment form factor are computed to next-to-leading order, including two-body currents. For inelastic scattering, two neutral current processes νd→ νnp , νd→ νnp and one charged current process νd→e +nn are computed to next-to-leading order. These depend on an isovector axial two-body matrix element whose value is yet to be fixed by experiment. Potential model calculations by Kubodera et al. and Ying et al. are reproduced for different values of the two-body matrix element. This implies that the differences between the two potential model calculations lie in their treatment of short distance physics. The charged current to neutral current νd cross-section ratio is confirmed to be insensitive to short distance physics, and the same ratio is obtained by potential models and the calculation presented here, within 5%, for incident neutrino energies up to 20 MeV. The two-body matrix element could be fixed using the parity violating process ed→enp .

Short strings and gluon propagator in the infrared region

We discuss how infrared region influence on short distance physics via new object, called “short string”. This object exists in confining theories and violates the operator product expansion. Most analytical results are obtained for the dual Abelian Higgs theory, while phenomenological arguments are given for QCD.