Model-independent Results Research Articles

Final model independent results of DAMA/LIBRA-phase1 and perspectives of phase2

This paper shortly summarizes the results obtained with the total exposure of 1.04 ton × yr collected by DAMA/LIBRA-phase1 deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. during 7 annual cycles. The DAMA/LIBRA-phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton × yr, corresponding to 14 annual cycles) give evidence at 9.3 σ C.L. for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radio-pure NaI(Tl) target. The modulation amplitude of the single-hit events in the (2–6) keV energy interval is: (0.0112 ± 0.0012) cpd/kg/keV; the measured phase is (144 ± 7) days and the measured period is (0.998 ± 0.002) yr, values well in agreement with those expected for DM particles. No systematic or side reaction able to mimic the exploited DM signature has been found or suggested by anyone over more than a decade. Some of the perspectives of the presently running DAMA/LIBRA-phase2 are outlined.

The action principle for generalized fluid motion including gyroviscosity

A general set of fluid equations that allow for energy-conserving momentum transport by gyroscopic motion of fluid elements is obtained. The equations are produced by a class of action principles that yield a large subset of the known fluid and magnetofluid models, including gyroviscosity. Analysis of the action principle yields broad, model-independent results regarding the conservation laws of energy and linear and angular momenta. The formalism is illustrated by studying fluid models with intrinsic angular momentum that may appear in the contexts of condensed matter, biological, and other areas of physics.

Implications of the Oklo Phenomenon in a Chiral Approach to Nuclear Matter

It has been customary to use data from the Oklo natural nuclear reactor to place bounds on the change that has occurred in the electromagnetic fine structure constant $\alpha$ over the last 2 billion years. Alternatively, an analysis could be based on a recently proposed expression for shifts in resonance energies which relates them to changes in both $\alpha$ and the average $m_q$ of the $u$ and $d$ current quark masses, and which makes explicit the dependence on mass number $A$ and atomic number $Z$. (Recent model independent results on hadronic $\sigma$-terms suggest sensitivity to the strange quark mass is negligible.) The most sophisticated analysis, to date, of the quark mass term invokes a calculation of the nuclear mean-field within the Walecka model of quantum hadrodynamics. We comment on this study and consider an alternative in which the link to low-energy quantum chromodynamics (QCD) and its pattern of chiral symmetry-breaking is more readily discernible. Specifically, we investigate the sensitivity to changes in the pion mass $M_\pi$ of a single nucleon potential determined by an in-medium chiral perturbation theory ($\chi$PT) calculation which includes virtual $\mathrm{\Delta}$-excitations. Subject to some reasonable assumptions about low-energy constants (LECs), we confirm that the $m_q$-contribution to resonance shifts is enhanced by a factor of 10 or so relative to the $\alpha$-term and deduce that the Oklo data for Sm imply that $|m_q(\mathrm{Oklo})- m_q(\mathrm{now})| \lesssim 10^{-9}m_q(\mathrm{now})$.

DARK MATTER INVESTIGATION BY DAMA AT GRAN SASSO

Experimental observations and theoretical arguments at Galaxy and larger scales have suggested that a large fraction of the Universe is composed by Dark Matter particles. This has motivated the DAMA experimental efforts to investigate the presence of such particles in the galactic halo by exploiting a model independent signature and very highly radiopure setup in deep underground. Few introductory arguments are summarized before presenting a review of the present model independent positive results obtained by the DAMA/NaI and DAMA/LIBRA setups at the Gran Sasso National Laboratory of the INFN. Implications and model dependent comparisons with other different kinds of results will be shortly addressed. Some arguments put forward in literature will be confuted.

Vector triplets at the LHC

Several popular extensions of the Standard Model predict extra vector fields that transform as triplets under the gauge group SU(2)_L. These multiplets contain Z' and W' bosons, with masses and couplings related by gauge invariance. We review some model-independent results about these new vector bosons, with emphasis on di-lepton and lepton-plus-missing-energy signals at the LHC.

Translationally invariant calculations of form factors, nucleon densities and momentum distributions for finite nuclei with short-range correlations included

Relying upon our previous treatment of the density matrices for nuclei (in general, nonrelativistic self-bound finite systems) we are studying a combined effect of center-of-mass motion and short-range nucleon-nucleon correlations on the nucleon density and momentum distributions in light nuclei (4He and 16O). Their intrinsic ground-state wave functions are constructed in the so-called fixed center-of-mass approximation, starting with mean-field Slater determinants modified by some correlator (e.g., after Jastrow or Villars). We develop the formalism based upon the Cartesian or boson representation, in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators for oscillatory quanta in the three different space directions, and get the own “Tassie-Barker” factors for each distribution and point out other model-independent results. After this separation of the center-of-mass motion effects we propose additional analytic means in order to simplify the subsequent calculations (e.g., within the Jastrow approach or the unitary correlation operator method). The charge form factors, densities and momentum distributions of 4He and 16O evaluated by using the well-known cluster expansions are compared with data, our exact (numerical) results and microscopic calculations.

Self-energy of a scalar charge near higher-dimensional black holes

We study the problem of self-energy of charges in higher-dimensional static spacetimes. Application of regularization methods of quantum field theory to calculation of the classical self-energy of charges leads to model-independent results. The correction to the self-energy of a scalar charge due to the gravitational field of black holes of the higher-dimensional Majumdar-Papapetrou spacetime is calculated exactly. It proves to be zero in even dimensions, but it acquires nonzero value in odd-dimensional spacetimes. The origin of the self-energy correction in odd dimensions is similar to the origin of the conformal anomalies in quantum field theory in even-dimensional spacetimes.

Addressing the multi-channel inverse problem at high energy colliders: a model-independent approach to the search for new physics with trileptons

We describe a method for interpreting trilepton searches at high energy colliders in a model-independent fashion and apply it to the recent searches at the Tevatron. The key step is to recognize that the trilepton signature is comprised of four experimentally very different channels defined by the number of τ leptons in the trilepton state. Contributions from these multiple channels to the overall experimental sensitivity (cross-section times branching ratio) are model-independent and can be parametrized in terms of relevant new particle masses. Given the trileptonic branching ratios of a specific model, these experimentally obtained multi-channel sensitivities can be combined to obtain a cross-section measurement that can be used to confront the model with data. Our model-independent results are more widely applicable than the current Tevatron trilepton results which are stated exclusively in terms of mSUGRA parameters of supersymmetry. The technique presented here can be expanded beyond trilepton searches to the more general ‘inverse problem’ of experimentally discriminating between competing models that seek to explain new physics discovered in multiple channels.

Color dipole picture of low-xDIS: Model-independent and model-dependent results

We present a detailed examination of the color-dipole picture (CDP) of low-$x$ deep inelastic scattering. We discriminate model-independent results, not depending on a specific parameterization of the dipole cross section, from model-dependent ones. The model-independent results include the ratio of the longitudinal to the transverse photoabsorption cross section at large $Q^2$, or equivalently the ratio of the longitudinal to the unpolarized proton structure function, $F_L (x,Q^2)=0.27 F_2 (x, Q^2)$, as well as the low-$x$ scaling behavior of the total photoabsorption cross section $\sigma_{\gamma^*p} (W^2, Q^2)=\sigma_{\gamma^*p} (\eta (W^2, Q^2))$ as $\log (1 / \eta (W^2, Q^2))$ for $\eta (W^2, Q^2) <1$, and as $1/\eta (W^2, Q^2)$ for $\eta (W^2, Q^2) \gg 1$. Here, $\eta (W^2, Q^2)$ denotes the low-$x$ scaling variable, $\eta (W^2, Q^2)=(Q^2 + m^2_0) / \Lambda^2_{sat} (W^2)$ with $\Lambda^2_{sat} (W^2)$ being the saturation scale. The model-independent analysis also implies $\lim\limits_{W^2\rightarrow\infty, Q^2 {\rm fixed}} \sigma_{\gamma^*p} (W^2, Q^2) / \sigma_{\gamma p} (W^2) \rightarrow 1$ at any $Q^2$ for asymptotically large energy, $W$. Consistency with pQCD evolution determines the underlying gluon distribution and the numerical value of $C_2 = 0.29$ in the expression for the saturation scale, $\Lambda^2 (W^2) \sim (W^2)^{C_2}$. In the model-dependent analysis, by restricting the mass of the actively contributing $q \bar q$ fluctuations by an energy-dependent upper bound, we extend the validity of the color-dipole picture to $x \cong Q^2 / W^2 \le 0.1$. The theoretical results agree with the world data on DIS for $0.036 {\rm GeV}^2 \le Q^2 \le 316 {\rm GeV}^2$.

Total nucleon-nucleon cross sections in largeNcQCD

We use contracted spin-flavor symmetry which emerges in the large ${N}_{c}$ limit of QCD to obtain relations between proton-proton and proton-neutron total cross sections for both polarized and unpolarized scattering. The formalism used is valid in the semiclassical regime in which the relative momentum of the incident nucleons is much larger than the inverse size of the nucleon, provided that certain technical assumptions are met. The relations should be phenomenologically useful provided that ${N}_{c}=3$ is sufficiently large so that the large ${N}_{c}$ results have at least semiquantitative predictive power. The relations are model independent in the sense that they depend on properties of large ${N}_{c}$ QCD only and not on any particular model-dependent details of the nucleon-nucleon interaction. We compare these model-independent results to the experimental data. We find the relation for spin-unpolarized scattering works well empirically. For the case of polarized scattering, the data are consistent with the relations, but the cross sections are too small to make sharp predictions.

B′s with direct decays: Tevatron and LHC discovery prospects in thebb¯+E̸Tchannel

We explore the discovery prospects for B'\bar{B}' pair production followed by direct decays B'->bX, where B' is a new quark and X is a long-lived neutral particle. We develop optimized cuts in the (m_B', m_X) plane and show that the 7 TeV LHC with an integrated luminosity of 1 (10) fb^-1 may exclude masses up to m_B' ~ 620 (800) GeV, completely covering the mass range allowed for new quarks that get mass from electroweak symmetry breaking. This analysis is applicable to other models with b\bar{b}+MET signals, including supersymmetric models with bottom squarks decaying directly to neutralinos, and models with exotic quarks decaying directly to GeV-scale dark matter. To accommodate these and other interpretations, we also present model-independent results for the b\bar{b}+MET cross section required for exclusion and discovery.

Model-independent data reductions of elastic proton–proton scattering

New developments in empirical analyses of the proton–proton differential cross section data at high energies are reported. Making use of an unconstrained model-independent parametrization for the scattering amplitude and two different fit procedures, all the experimental data in the center-of-mass energy interval 19.4–62.5 GeV are quite well described (optical point and data above the region of Coulomb-nuclear interference). The contributions from the real and imaginary parts of the amplitude beyond the forward direction are discussed and compared with the results from previous analyses and phenomenological models. Extracted overlap functions (impact parameter space) are outlined and a critical discussion on model-independent analyses and results are also presented.

Theoretical view of SPS and RHIC dilepton measurements

In this contribution I present a review on the actual status of dilepton measurements at SPS and RHIC energies and the current theoretical interpretations. Model independent results will be pointed out for both energies. Due to partially conflicting theoretical concepts I will highlight the open questions that may be solved by extended theoretical as well as experimental studies.

Measurement ofW-Boson Polarization in Top-Quark Decay inpp¯Collisions ats=1.96 TeV

We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb^-1 of ppbar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c^2, three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f_0) and right-handed (f_+) W bosons yields the model-independent results f_0 = 0.88 \pm 0.11 (stat) \pm 0.06 (syst) and f_+ = -0.15 \pm 0.07 (stat) \pm 0.06 (syst) with a correlation coefficient of -0.59. A measurement of f_0 (f_+) constraining f_+ (f_0) to its standard model value of 0.0 (0.7) yields f_0 = 0.70 \pm 0.07 (stat) \pm 0.04 (syst) (f_+ = -0.01 \pm 0.02 (stat) \pm 0.05 (syst)). All these results are consistent with standard model expectations.

Direct method for imaging elemental distribution profiles with long-period x-ray standing waves

A model-independent Fourier-inversion method for imaging elemental profiles from multilayer and total-external reflection x-ray standing wave (XSW) data is developed for the purpose of understanding the assembly of atoms, ions, and molecules at well-defined interfaces in complex environments. The direct-method formalism is derived for the case of a long-period XSW generated by low-angle specular reflection in an attenuating overlayer medium. It is validated through comparison with simulated and experimental data to directly obtain an elemental distribution contained within the overlayer. We demonstrate this formalism by extracting the one-dimensional profile of Ti normal to the surface for a ${\text{TiO}}_{2}/\text{Si}/\text{Mo}$ trilayer deposited on a Si substrate using the $\text{Ti}\text{ }K\ensuremath{\alpha}$ fluorescence yield measured in air and under an aqueous electrolyte. The model-independent results demonstrate reduced coherent fractions for the in situ results associated with an incoherency of the x-ray beam (which are attributed to fluorescence excitation by diffusely or incoherently scattered x-rays). The uniqueness and limitations of the approach are discussed.

High-order time expansion path integral ground state

The feasibility of path integral Monte Carlo ground state calculations with very few beads using a high-order short-time Green's function expansion is discussed. An explicit expression of the evolution operator which provides dramatic enhancements in the quality of ground-state wave functions is examined. The efficiency of the method makes possible to remove the trial wave function and thus obtain completely model-independent results still with a very small number of beads. If a single iteration of the method is used to improve a given model wave function, the result is invariably a shadow-type wave function, whose precise content is provided by the high-order algorithm employed.

Wave-train-induced termination of weakly anchored vortices in excitable media

A free vortex in excitable media can be displaced and removed by a wave train. However, simple physical arguments suggest that vortices anchored to large inexcitable obstacles cannot be removed similarly. We show that unpinning of vortices attached to obstacles smaller than the core radius of the free vortex is possible through pacing. The wave-train frequency necessary for unpinning increases with the obstacle size and we present a geometric explanation of this dependence. Our model-independent results suggest that decreasing excitability of the medium can facilitate pacing-induced removal of vortices in cardiac tissue.

FORWARD PHYSICS AT THE LHC: ELASTIC SCATTERING

The following effects in the nearly forward ("soft") region of the LHC are proposed to be investigated: • At small |t| the fine structure of the cone (Pomeron) should be scrutinized: (a) a break of the cone near t ≈ -0.1 GeV 2, due to the two-pion threshold, and required by t-channel unitarity, and (b) possible small-period oscillations between t = 0 and the dip region. • In measuring the elastic pp scattering and total pp cross-section at the LHC, the experimentalists are urged to treat the total cross-section σt, the ratio ρ of real to imaginary part of the forward scattering amplitude, the forward slope B and the luminosity [Formula: see text] as free parameters, and to publish model-independent results on dN/dt. • Of extreme interest are the details of the expected diffraction minimum in the differential cross-section. Its position, expected in the interval 0.4 &lt; -t &lt; 1 GeV 2 at the level of about 10-2 mb · GeV -2–10-1 mb · GeV -2, cannot be predicted unambiguously, and its depth, i.e. the ratio of dσ/dt at the minimum to that at the subsequent maximum (about -t = 5 GeV 2, which is about 5) is of great importance. • The expected slow-down with increasing |t| of the shrinkage of the second cone (beyond the dip-bump), together with the transition from an exponential to a power decrease in -t, will be indicative of the transition from "soft" to "hard" physics. Explicit models are proposed to help in quantifying this transition. • In a number of papers a limiting behavior, or saturation of the black disk limit (BDL), was predicted. This controversial phenomenon shows that the BDL may not be the ultimate limit, instead a transition from shadow to antishadow scattering may by typical of the LHC energy scale.

Generic features of the spectrum of trapped polarized fermions

We show that bimodal radio frequency spectra universally arise at intermediate temperatures in models of strongly interacting trapped Fermi gases. The bimodality is independent of superfluidity or pseudogap physics, depending only on the functional form of the equation of state---which is constrained by dimensional analysis at low temperatures and the virial expansion at high temperatures. In addition to these model independent results, we present a simple calculation of the radio frequency line shape of a highly polarized Fermi gas which uses energetic considerations to include final state interactions. While this model only qualitatively captures the line shapes observed in the experiments, it provides a conceptually clean and powerful technique for estimating the energy scales and how they vary with experimental parameters.

Cosmography off(R)gravity

It is nowadays accepted that the universe is undergoing a phase of accelerated expansion as tested by the Hubble diagram of type Ia supernovae (SNeIa) and several large scale structure observations. Future SNeIa surveys and other probes will make it possible to better characterize the dynamical state of the universe, renewing the interest in cosmography which allows a model independent analysis of the distance-redshift relation. On the other hand, fourth order theories of gravity, also referred to as $f(R)$ gravity, have attracted a lot of interest since they could be able to explain the accelerated expansion without any dark energy. We show here how it is possible to relate the cosmographic parameters (namely, the deceleration ${q}_{0}$, the jerk ${j}_{0}$, the snap ${s}_{0}$, and the lerk ${l}_{0}$ parameters) to the present-day values of $f(R)$ and its derivatives ${f}^{(n)}(R)={d}^{n}f/d{R}^{n}$ (with $n=1$, 2, 3), thus offering a new tool to constrain such higher order models. Our analysis thus offers the possibility to relate the model independent results coming from cosmography to the theoretically motivated assumptions of $f(R)$ cosmology.