Showing papers in "International Journal of Modern Physics A in 2015"

LHCb detector performance

Abstract: The LHCb detector is a forward spectrometer at the Large Hadron Collider (LHC) at CERN. The experiment is designed for precision measurements of CP violation and rare decays of beauty and charm hadrons. In this paper the performance of the various LHCb sub-detectors and the trigger system are described, using data taken from 2010 to 2012. It is shown that the design criteria of the experiment have been met. The excellent performance of the detector has allowed the LHCb collaboration to publish a wide range of physics results, demonstrating LHCb's unique role, both as a heavy flavour experiment and as a general purpose detector in the forward region.

Neutrinoless double-beta decay: A probe of physics beyond the Standard Model

Abstract: In the Standard Model the total lepton number is conserved. Thus, neutrinoless double-β decay, in which the total lepton number is violated by two units, is a probe of physics beyond the Standard Model. In this review we consider the basic mechanism of neutrinoless double-β decay induced by light Majorana neutrino masses. After a brief summary of the present status of our knowledge of neutrino masses and mixing and an introduction to the seesaw mechanism for the generation of light Majorana neutrino masses, in this review we discuss the theory and phenomenology of neutrinoless double-β decay. We present the basic elements of the theory of neutrinoless double-β decay, our view of the present status of the challenging problem of the calculation of the nuclear matrix element of the process and a summary of the experimental results.

Four-quark hadrons: An updated review

Abstract: The past decade witnessed a remarkable proliferation of exotic charmonium-like resonances discovered at accelerators. In particular, the recently observed charged states are clearly not interpretable as mesons. Notwithstanding the considerable advances on the experimental side, conflicting theoretical descriptions do not seem to provide a definitive picture about the nature of the so-called XYZ particles. We present here a comprehensive review about this intriguing topic, discussing both those experimental and theoretical aspects which we consider relevant to make further progress in the field. At this state of progress, XYZ phenomenology speaks in favor of the existence of compact four-quark particles (tetraquarks) and we believe that realizing this instructs us in the quest for a firm theoretical framework.

GUP-Corrected Thermodynamics for all Black Objects and the Existence of Remnants

Abstract: Based on the universality of the entropy-area relation of a black hole, and the fact that the generalized uncertainty principle (GUP) adds a logarithmic correction term to the entropy in accordance with most approaches to quantum gravity, we argue that the GUP-corrected entropy-area relation is universal for all black objects. This correction to the entropy produces corrections to the thermodynamics. We explicitly calculate these corrections for three types of black holes: Reissner–Nordstrom, Kerr and charged AdS black holes, in addition to spinning black rings. In all cases, we find that they produce a remnant. Even though the GUP-corrected entropy-area relation produces the logarithmic term in the series expansion, we need to use the full form of the GUP-corrected entropy-area relation to get remnants for these black holes.

Lifetimes and heavy quark expansion

Abstract: Kolya Uraltsev was one of the inventors of the Heavy Quark Expansion (HQE), that describes inclusive weak decays of hadrons containing heavy quarks and in particular lifetimes. Besides giving a pedagogic introduction to the subject, we review the development and the current status of the HQE, which just recently passed several non-trivial experimental tests with an unprecedented precision. In view of many new experimental results for lifetimes of heavy hadrons, we also update several theory predictions: , τ(Bs)/τ(Bd) = 1.001 ±0.002, τ(Λb)/τ(Bd) = 0.935 ±0.054 and . The theoretical precision is currently strongly limited by the unknown size of the non-perturbative matrix elements of four-quark operators, which could be determined with lattice simulations.

Analysis of the Zc(4200) as axial-vector molecule-like state

Abstract: In this paper, we assume the Zc(4200) as the color octet–octet type axial-vector molecule-like state, and construct the color octet–octet type axial-vector current to study its mass and width with the QCD sum rules. The numerical values MZc(4200) = 4.19 ± 0.08GeV and ΓZc(4200) ≈ 334MeV are consistent with the experimental data MZc(4200) = 4196−29+31 −13+17MeV and ΓZc(4200) = 370−70+70 −132+70MeV, and support assigning the Zc(4200) to be the color octet–octet type molecule-like state with JPC = 1+−. Furthermore, we discuss the possible assignments of the Zc(3900), Zc(4200) and Z(4430) as the diquark–antidiquark type tetraquark states with JPC = 1+−.

Tetraquark state candidates: $Y$(4140), $Y$(4274) and $X$(4350)

Abstract: In this paper, we tentatively assign the Y(4140), Y(4274) and X(4350) to be the scalar and tensor tetraquark states, respectively, and study them with the QCD sum rules. In the operator product expansion, we take into account the vacuum condensates up to dimension-10. In calculations, we use the formula to determine the energy scales of the QCD spectral densities. The numerical results favor assigning the Y(4140) to be the JPC = 2++ diquark–antidiquark type tetraquark state, and disfavor assigning the Y(4274) and X(4350) to be the 0++ or 2++ tetraquark states.

Nonstrange and strange pentaquarks with hidden charm

Abstract: Nonstrange and strange pentaquarks with hidden charm are considered as diquark–diquark–antiquark composite systems. Spin and isospin content of such exotic states is discussed and masses are evaluated.

Elastic scattering and diffractive dissociation in the light of LHC data

Abstract: We study the behavior of elastic and diffractive proton dissociation cross sections at high energy First, we describe what would be expected to be observed at the Large Hadron Collider (LHC) based on conventional Regge theory We emphasize the tension between these expectations and the recent LHC measurements, and we discuss the possibilty to modify the classic Reggeon Field Theory (RFT) in a physically-motivated way so as to accommodate the tendencies observed at the LHC As a result, we show that we are able to achieve a "global" description of the wide variety of high energy elastic and diffractive data that are presently available, particularly from the LHC experiments The model is based on only one pomeron pole, but includes multi-pomeron interactions and, significantly, includes the transverse momentum dependence of intermediate partons as a function of their rapidity, which provides the rapidity dependence of the multi-pomeron vertices We give predictions for diffractive observables at LHC, and higher, energies

Corrections to entropy and thermodynamics of charged black hole using generalized uncertainty principle

Abstract: Recently, there has been much attention devoted to resolving the quantum corrections to the Bekenstein–Hawking (black hole) entropy, which relates the entropy to the cross-sectional area of the black hole horizon. Using generalized uncertainty principle (GUP), corrections to the geometric entropy and thermodynamics of black hole will be introduced. The impact of GUP on the entropy near the horizon of three types of black holes: Schwarzschild, Garfinkle–Horowitz–Strominger and Reissner–Nordstrom is determined. It is found that the logarithmic divergence in the entropy-area relation turns to be positive. The entropy S, which is assumed to be related to horizon's two-dimensional area, gets an additional terms, for instance , where α is the GUP parameter.

Phenomenological Description of the Interior of the Schwarzschild Black Hole

Abstract: We discuss a sufficiently large four-dimensional Schwarzschild black hole which is in equilibrium with a heat bath. In other words, we consider a black hole which has grown up from a small one in the heat bath adiabatically. We express the metric of the interior of the black hole in terms of two functions: One is the intensity of the Hawking radiation, and the other is the ratio between the radiation energy and the pressure in the radial direction. Especially in the case of conformal matters we check that it is a self-consistent solution of the semiclassical Einstein equation, Gμν = 8πG〈Tμν〉. It is shown that the strength of the Hawking radiation is proportional to the c-coefficient, that is, the coefficient of the square of the Weyl tensor in the four-dimensional Weyl anomaly.

Luminosity goals for a 100-TeV pp collider

Abstract: We consider diverse examples of science goals that provide a framework to assess luminosity goals for a future 100-TeV proton-proton collider.

Searching for Elko dark matter spinors at the CERN LHC

Abstract: The aim of this paper is to explore the possibility of discovering a fermionic field with mass dimension one, the Elko field, in the Large Hadron Collider. Due to its mass dimension, an Elko can only interact either with Standard Model spinors and gauge fields at one-loop order or at tree level through a quartic interaction with the Higgs field. In this Higgs portal scenario, the Elko is a viable candidate to a dark matter constituent which has been shown to be compatible with relic abundance measurements from WMAP and direct dark matter searches. We propose a search strategy for this dark matter candidate in the channel at the LHC. We show the LHC potential to discover the Elko considering a triple Higgs–Elkos coupling as small as ~0.5 after 1 ab-1 of integrated luminosity. Some phenomenological consequences of this new particle and its collider signatures are also discussed.

A comprehensive model of soft interactions in the LHC era

Abstract: In this review we present our model which is an example of the self-consistent approach that incorporates our theoretical understanding of long distance physics, based both on N = 4 SYM for strong coupling and on the matching with the perturbative QCD approach. We demonstrate how important and decisive the LHC data were on strong interactions which led us to a set of the phenomenological parameters that fully confirmed our theoretical expectations, and produced a new picture of the strong interaction at high energy. We also show how far we have come towards creating a framework for the description of minimal bias events for high energy scattering without generating Monte Carlo codes.

Improved fD(s)∗, fB(s)∗ and fBc from QCD Laplace sum rules

Abstract: Anticipating future precise measurements of the D- and B-like (semi)leptonic and hadronic decays for alternative determinations of the CKM mixing angles, we pursue our program on the D- and B-like mesons by improving the estimates of fD(s)∗ and fB(s)∗ (analogue to fπ) by using the well-established (inverse) Laplace sum rules (LSR) and/or their suitable ratios less affected by the systematics, which are known to N2LO pQCD and where the complete d = 6 nonperturbative condensate contributions are included. The convergence of the PT series is analyzed by an estimate of the N3LO terms based on geometric growth of the coefficients. In addition to the standard LSR variable τ and the QCD continuum threshold tc stability criteria, we extract our optimal results by also requiring stability on the variation of the arbitrary QCD subtraction point μ which reduces the errors in the analysis. We complete the study of the open bottom states by an estimate of fBc. Our results summarized in Tables 3 and 4 are compared with some other recent sum rules and lattice estimates.

Colored knot polynomials: HOMFLY in representation [2, 1]

Abstract: This paper starts a systematic description of colored knot polynomials, beginning from the first non-(anti)symmetric representation R = [2, 1]. The project involves several steps: (i)parametrization of big families of knots a la [A. Mironov and A. Morozov, arXiv:1506.00339],(ii)evaluating Racah/mixing matrices for various numbers of strands in various representations a la [A. Mironov, A. Morozov and An. Morozov, J. High Energy Phys. 03, 034 (2012), arXiv:1112.2654],(iii)tabulating and collecting the results at http://www.knotebook.org. In this paper, we discuss only the representation R = [2, 1] and construct all necessary ingredients that allow one to evaluate knot/links represented by three-strand closed parallel braids with inserted double-fat fingers. In particular, it is used to evaluate knots from a 7-parametric family. This family contains over 80% of knots with up to 10 intersections, but does not include mutants.

Neutrino mixing with nonzero θ13 and CP violation in the 3-3-1 model based on S4 flavor symmetry

Abstract: We propose a 3-3-1 model with neutral fermions based on A4 flavor symmetry responsible for fermion masses and mixings with nonzero θ13. To get realistic neutrino mixing, we just add a new SU(3)L triplet being in 3 under A4. The neutrinos get small masses from two SU(3)L antisextets and one SU(3)L triplet. The model can fit the present data on neutrino masses and mixing as well as the effective mass governing neutrinoless double beta decay. Our results show that the neutrino masses are naturally small and a little deviation from the tri-bimaximal neutrino mixing form can be realized. The Dirac CP violation phase δ is predicted to either 5.41∘ or 354.59∘ with θ23≠π 4.

A stochasticity threshold in holography and the instability of AdS

Abstract: We give strong numerical evidence that a self-interacting probe scalar field in AdS, with only a few modes turned on initially, will undergo fast thermalization only if it is above a certain energetic threshold. Below the threshold the energy stays close to constant in a few modes for a very long time instead of cascading quickly. This indicates the existence of a Strong Stochasticity Threshold (SST) in holography. The idea of SST is familiar from certain statistical mechanical systems, and we suggest that it exists also in AdS gravity. This would naturally reconcile the generic nonlinear instability of AdS observed by Bizon and Rostworowski, with the Fermi–Pasta–Ulam–Tsingou-like quasiperiodicity noticed recently for some classes of initial conditions. We show that our simple setup captures many of the relevant features of the full gravity-scalar system.

Tolman–Oppenheimer–Volkoff equations in nonlocal $f(R)$ gravity

Abstract: Nonlocal f(R) gravity was proposed as a powerful alternative to general relativity (GR). This theory has potentially adverse implications for infrared (IR) regime as well as ultraviolet (UV) early epochs. However, there are a lot of powerful features, making it really user-friendly. A scalar–tensor frame comprising two auxiliary scalar fields is used to reduce complex action. However, this is not the case for the modification complex which plays a distinct role in modified theories for gravity. In this work, we study the dynamics of a static, spherically symmetric object. The interior region of space–time had rapidly filled the perfect fluid. However, it is possible to derive a physically based model which relates interior metric to nonlocal f(R). The Tolman–Oppenheimer–Volkoff (TOV) equations would be a set of first-order differential equations from which we can deduce all mathematical (physical) truths and derive all dynamical objects. This set of dynamical equations govern pressure p, density ρ, mass m and auxiliary fields {ψ, ξ}. The full conditional solutions are evaluated and inverted numerically to obtain exact forms of the compact stars Her X-1, SAX J 1808.4-3658 and 4U 1820-30 for nonlocal Starobinsky model of f(◻-1 R) = ◻-1 R+α(◻-1 R)2. The program solves the differential equations numerically using adaptive Gaussian quadrature. An ascription of correctness is supposed to be an empirical equation of state for star which is informative in so far as it excludes an alternative nonlocal approach to compact star formation. This model is most suited for astrophysical observation.

String cosmology — Large-field inflation in string theory

Abstract: This is a short review of string cosmology. We wish to connect string-scale physics as closely as possible to observables accessible to current or near-future experiments. Our possible best hope to do so is a description of inflation in string theory. The energy scale of inflation can be as high as that of Grand Unification (GUT). If this is the case, this is the closest we can possibly get in energy scales to string-scale physics. Hence, GUT-scale inflation may be our best candidate phenomenon to preserve traces of string-scale dynamics. Our chance to look for such traces is the primordial gravitational wave, or tensor mode signal produced during inflation. For GUT-scale inflation this is strong enough to be potentially visible as a B-mode polarization of the cosmic microwave background (CMB). Moreover, a GUT-scale inflation model has a trans-Planckian excursion of the inflaton scalar field during the observable amount of inflation. Such large-field models of inflation have a clear need for symmetry protection against quantum corrections. This makes them ideal candidates for a description in a candidate fundamental theory like string theory. At the same time the need of large-field inflation models for UV completion makes them particularly susceptible to preserve imprints of their string-scale dynamics in the inflationary observables, the spectral index ns and the fractional tensor mode power r. Hence, we will focus this review on axion monodromy inflation as a mechanism of large-field inflation in string theory.

A holographic description of the Schwinger effect in a confining gauge theory

Abstract: This is a review of the recent progress on a holographic description of the Schwinger effect. In 2011, Semenoff and Zarembo proposed a scenario to study the Schwinger effect in the context of the AdS/CFT correspondence. The production rate of quark–antiquark pairs was computed in the Coulomb phase. In particular, it provided the critical value of external electric field, above which particles are freely created and the vacuum decays catastrophically. Then the potential analysis in the holographic approach was invented and it enabled us to study the Schwinger effect in the confining phase as well. A remarkable feature of the Schwinger effect in the confining phase is to exhibit another kind of the critical value, below which the pair production cannot occur and the vacuum of the system is nonperturbatively stable. The critical value is tantamount to the confining string tension. We computed the pair production rate numerically and introduced new exponents associated with the critical electric fields.

New and Old about Renormalons: in Memoriam Kolya Uraltsev

Abstract: I summarize what we know of renormalons from the 1970s and 80s: their uses and theoretical status. It is emphasized that renormalons in QCD are closely related to the Wilsonean operator product expansion (OPE) — a setup ideally suited for dealing with the factorially divergent series reflecting infrared dynamics. I discuss a breakthrough proposal due to Uraltsev et al. to use renormalons to evaluate nonperturbative (power) corrections in the processes without OPE. Some fresh ideas which were put forward recently are briefly discussed too, with emphasis on a possible relationship between resurgence via trans-series and OPE. This article is devoted to the memory of my friend Kolya Uraltsev. I should emphasize that these are my personal recollections. Other people who closely knew Kolya may or may not agree with my opinions.

Field-dependent BRST-anti-BRST Lagrangian transformations

Abstract: We continue our study of finite BRST–anti-BRST transformations for general gauge theories in Lagrangian formalism, initiated in [arXiv:1405.0790 [hep-th] and arXiv:1406.0179 [hep-th]], with a doublet λa, a = 1, 2, of anticommuting Grassmann parameters, and prove the correctness of the explicit Jacobian in the partition function announced in [arXiv:1406.0179 [hep-th]], which corresponds to a change of variables with functionally dependent parameters λa = UaΛ induced by a finite Bosonic functional Λ(ϕ, π, λ) and by the anticommuting generators Ua of BRST–anti-BRST transformations in the space of fields ϕ and auxiliary variables πa, λ. We obtain a Ward identity depending on the field-dependent parameters λa and study the problem of gauge dependence, including the case of Yang–Mills theories. We examine a formulation with BRST–anti-BRST symmetry breaking terms, additively introduced into the quantum action constructed by the Sp(2)-covariant Lagrangian rules, obtain the Ward identity and investigate the gauge independence of the corresponding generating functional of Green's functions. A formulation with BRST symmetry breaking terms is developed. It is argued that the gauge independence of the above generating functionals is fulfilled in the BRST and BRST–anti-BRST settings. These concepts are applied to the average effective action in Yang–Mills theories within the functional renormalization group approach.

Geometric phases modified by a Lorentz-symmetry violation background

Abstract: We analyze the nonrelativistic quantum dynamics of a single neutral spin-half particle, with nonzero magnetic and electric dipole moments, moving in an external electromagnetic field in the presence of a Lorentz-symmetry violating background. We also study the geometric phase for this model taking in account the influence of the parameter that breaks the Lorentz-symmetry. These geometric phases are used to impose an upper bound on the background magnitude.

The Past and Future of Light Dark Matter Direct Detection

Abstract: We review the status and future of direct searches for light dark matter. We start by answering the question: "Whatever happened to the light dark matter anomalies?" i.e. the fate of the potential dark matter signals observed by the CoGeNT, CRESST-II, CDMS-Si and DAMA/LIBRA experiments. We discuss how the excess events in the first two of these experiments have been explained by previously underestimated backgrounds. For DAMA, we summarize the progress and future of mundane explanations for the annual modulation reported in its event rate. Concerning the future of direct detection, we focus on the irreducible background from solar neutrinos. We explain broadly how it will affect future searches and summarize efforts to mitigate its effects.

Probing Dark Energy Models with Neutrons

Abstract: There is a deep connection between cosmology - the science of the infinitely large - and particle physics - the science of the infinitely small. This connection is particularly manifest in neutron particle physics. Basic properties of the neutron { its Electric Dipole Moment and its lifetime { are intertwined with baryogenesis and nucleosynthesis in the early Universe. I will cover this topic in the first part, that will also serve as an introduction (or rather a quick recap) of neutron physics and Big Bang cosmology. Then, the rest of the manuscript will be devoted to a new idea: using neutrons to probe models of Dark Energy. In the second part, I will present the chameleon theory: a light scalar field accounting for the late accelerated expansion of the Universe, which interacts with matter in such a way that it does not mediate a fifth force between macroscopic bodies. However, neutrons can alleviate the chameleon mechanism and reveal the presence of the scalar field with properly designed experiments. In the third part, I will describe a recent experiment performed with a neutron interferometer at the Institut Laue Langevin that sets already interesting constraints on the chameleon theory. Last, the chameleon field can be probed by measuring the quantum states of neutrons bouncing over a mirror. In the fourth part I will present the status and prospects of the GRANIT experiment at the ILL.

Nonlocal quantum field theory without acausality and nonunitarity at quantum level: Is SUSY the key?

Abstract: The realization of a nonlocal quantum field theory without losing unitarity, gauge invariance and causality is investigated. It is commonly retained that such a formulation is possible at tree level, but at quantum level acausality is expected to reappear at one loop. We suggest that the problem of acausality is, in a broad sense, similar to the one about anomalies in quantum field theory. By virtue of this analogy, we suggest that acausal diagrams resulting from the fermionic sector and the bosonic one might cancel each other, with a suitable content of fields and suitable symmetries. As a simple example, we show how supersymmetry can alleviate this problem in a simple and elegant way, i.e. by leading to exact cancellations of harmful diagrams, to all orders of perturbation theory. An infinite number of divergent diagrams cancel each other by virtue of the nonrenormalization theorem of supersymmetry. However, supersymmetry is not enough to protect a theory from all acausal divergences. For instance, acausal contributions to supersymmetric corrections to D-terms are not protected by supersymmetry. On the other hand, we show in detail how supersymmetry also helps in dealing with D-terms: divergences are not canceled but they become softer than in the nonsupersymmetric case. The supergraphs' formalism turns out to be a powerful tool to reduce the complexity of perturbative calculations.

Inconstant Planck’s constant

Abstract: Motivated by the Dirac idea that fundamental constants are dynamical variables and by conjectures on quantum structure of space–time at small distances, we consider the possibility that Planck constant ℏ is a time depending quantity, undergoing random Gaussian fluctuations around its measured constant mean value, with variance σ2 and a typical correlation timescale Δt. We consider the case of propagation of a free particle and a one-dimensional harmonic oscillator coherent state, and show that the time evolution in both cases is different from the standard behavior. Finally, we discuss how interferometric experiments or exploiting coherent electromagnetic fields in a cavity may put effective bounds on the value of τ = σ2Δt.

Exotic mesons with hidden charm as diquark–antidiquark states

Abstract: Exotic mesons with hidden strange (ss) and heavy quark pairs (QQ), where Q = c, b, are considered as diquark–antidiquark systems, (Qs) ⋅ (Qs) Taking into account that these states can recombinate into two-meson ones, we study the interplay of these states in terms of the dispersion relation D-function technique The classification of exotic mesons is discussed, coefficients for decay modes are given, predictions for new states are presented The nonet structure for (Qq) ⋅ (Qq), (Qs) ⋅ (Qs), (Qq) ⋅ (Qs)-states (q = u,d) is suggested