HEP Phenomenology·hep-ph
21 papers—14 primary·7 cross-listed·reconstructed*
Yuval Grossman🇺🇸 · Philip Tanedo🇺🇸
We review the flavor structure of the Standard Model and the ways in which the flavor parameters are measured. This is an extended writeup of the TASI 2016 lectures on flavor physics. Earlier versions of these lectures were presented at pre-SUSY 2015 and Cornell University's Physics 7661 course in 2010.
Jose Carpio🇵🇪 · E. Massoni🇵🇪 · A.M. Gago🇵🇪
We re-examine the matter neutrino oscillation probabilities considering the decoherence phenomenon as a sub-leading effect. In this paper we point out the relevance of having the correct interpretation of the decoherence matrix in the different quantum bases, within the framework of neutrino oscillation probabilities in matter. Based on this treatment we develop an analytical formula for matter neutrino oscillation probabilities for three generations, with a range of application up to the decoherence parameter GeV. We observe that, due to decoherence, the amplitudes of the neutrino/antineutrino oscillation probabilities increase in an energy independent way. We also find that decoherence can reduce the absolute value of the CP asymmetry, relative to its value at the pure oscillation case. As a side effect we have found a degeneracy between the decoherence parameter and the CP violation phase .
Debajyoti Choudhury🇮🇳 · Divya Sachdeva🇮🇳
Recent results from direct detection experiments such as LUX, PANDAX-II and XENON100 have imposed severe constraints on the multi-GeV mass window in various dark matter (DM) models. However, many of these experiments are not sensitive to MeV scale DM as the corresponding recoil energies are, largely, lower than the detector thresholds. Re-examining the light scalar DM in a model-independent approach, we find that while the parameter space can be constrained using cosmological and astrophysical observations, a significantly large fraction is still viable. We further demonstrate that the remaining parameter space lends itself to the possibility of discovery at both direct detection experiments (such as CRESST-II) as well as in a low-energy collider such as Belle-II.
Mayumi Aoki🇯🇵 · Daiki Kaneko🇯🇵 · Jisuke Kubo🇯🇵
We discuss radiative seesaw models, in which an exact symmetry is imposed. Due to the exact symmetry, neutrino masses are generated at a two-loop level and at least two extra stable electrically neutral particles are predicted. We consider two models: one has a multi-component dark matter system and the other one has a dark radiation in addition to a dark matter. In the multi-component dark matter system, non-standard dark matter annihilation processes exist. We find that they play important roles in determining the relic abundance and also responsible for the monochromatic neutrino lines resulting from the dark matter annihilation process. In the model with the dark radiation, the structure of the Yukawa coupling is considerably constrained and gives an interesting relationship among cosmology, lepton flavor violating decay of the charged leptons and the decay of the inert Higgs bosons.
Exclusive light meson production processes possible to be measured at RHIC and LHC accelerators are briefly described. This includes Pomeron and photon induced continuum of pions and kaons as well as and resonant production. Next, GenEx, a new Monte Carlo generator recently developed in Cracow, is presented. Its purpose is to generate resonant and non-resonant pion and kaon production and diffractive Bremsstrahlung. Its future development will take into account spin (polarization) effects and simulate corrections due to absorption and re-scattering.
Alejandro Mariano · Daniel Badagnani · Cesar Barbero
In this paper we implement for the first time the use of a {\pi}N{\Delta}(1232) vertex interaction containing both first and second order derivative terms, as required by renormalization considerations. As as was previously shown both interactions present formal problems, but can be implemented pertubatively. We put an end point to the discussion of which type of interaction is the apropriate one: both the usual pi-derivative and the "spin 3/2" gauge invariant that include also a derivative in the {\Delta} field should be included in amplitude calculations. We show that when working within a tree level approach the description of total {\pi}N{\Delta} scattering in the different channels is improved.
In light of the observed Galactic center gamma-ray excess, we investigate a simplified model, for which the scalar dark matter interacts with quarks through a pseudoscalar mediator. The viable regions of the parameter space, that can also account for the relic density and evade the current searches, are identified, if the low-velocity dark matter annihilates through an -channel off-shell mediator mostly into , and/or annihilates directly into two on-shell mediators, which subsequently decay into the quark pairs. These two kinds of annihilations are wave. The projected monojet limit set by the high luminosity LHC sensitivity could constrain the favored parameter space, where the mediator's mass is larger than the dark matter mass by a factor of 2. We show that the projected sensitivity of 15-year Fermi-LAT observations of dwarf spheroidal galaxies can provide a stringent constraint on the most parameter space allowed in this model. If the on-shell mediator channel contributes to the dark matter annihilation cross sections over 50, this model with a lighter mediator can be probed in the projected PICO-500L experiment.
Guang Hua Duan🇨🇳 · Wenyu Wang🇨🇳 · Lei Wu🇨🇳 · Jin Min Yang🇨🇳 · Jun Zhao🇨🇳
Given the recent constraints from the dark matter (DM) direct detections, we examine a light GeV-scale (2-30 GeV) neutralino DM in the alignment limit of the Minimal Supersymmetric Standard Model (MSSM). In this limit without decoupling, the heavy CP-even scalar plays the role of the Standard Model (SM) Higgs boson while the other scalar can be rather light so that the DM can annihilate through the resonance or into a pair of to achieve the observed relic density. With the current collider and cosmological constraints, we find that such a light neutralino DM above 6 GeV can be excluded by the XENON-1T (2017) limits while the survivied parameter space below 6 GeV can be fully covered by the future germanium-based light dark matter detections (such as CDEX), by the Higgs coupling precison measurements or by the production process at an electron-positron collider (Higgs factory).
I show that with the discovery of the Higgs boson we have entered a new phase of our understanding of nature. This leads us towards a paradigm shift in the search for possible new physics, away from major extensions like supersymmetry towards minimalistic extensions, that largely preserve the structure of the standard model. To discover such new physics, precision may be more important than energy. Precision = Discovery! A possible path for the future is sketched.
D. Colladay🇺🇸 · J. P. Noordmans🇵🇹 · R. Potting🇵🇹
CPT and Lorentz violation in the photon sector is described within the minimal Standard-Model Extension by a dimension-3 Chern-Simons-like operator parametrized by a four-vector parameter that has been very tightly bounded by astrophysical observations. On the other hand, in the context of the electroweak gauge sector of the Standard-Model Extension, CPT and Lorentz violation is described similarly, by dimension-3 operators parametrized by four-vector parameters and . In this work, we investigate in detail the effects of the resulting CPT and Lorentz violation in the photon and -boson sectors upon electroweak-symmetry breaking. In particular, we show that for the photon sector the relevant Lorentz-violating effects are described at lowest order by the term, but that there are higher-order momentum-dependent effects due to photon- boson mixing. As bounds on CPT and Lorentz violation in the sector are relatively weak, these effects could be important phenomenologically. We investigate these effects in detail in this work.
Wolfgang Lucha🇦🇹 · Dmitri Melikhov🇦🇹 · Hagop Sazdjian🇫🇷
Scrutinizing the scattering of ordinary mesons in the limiting case of the number of colour degrees of freedom of quantum chromodynamics approaching infinity, we formulate Feynman-diagram selection criteria and from these deduce rigorous self-consistency conditions for the manifestation of a tetraquark, a two-quark-two-antiquark bound state, as a pole in the corresponding amplitudes. Our constraints bear rather far-reaching consequences: In particular, all flavour-exotic tetraquarks, composed of four (anti)quarks of disparate flavour, must come in, at least, two variants differing in (and thus readily identifiable by) the large- behaviour of their couplings to two ordinary mesons. Quite generally, irrespective of their flavour composition, all tetraquarks prove to be narrow. Their decay rates behave, for large like and thus decrease faster than those of ordinary mesons.
With the advent of very powerful particle accelerators, such as RHIC and the LHC, it becomes possible to study QCD in high energy collisions, in which the gluon content of the proton or nucleus is probed and its density becomes often large enough for nonlinear effects to play a role. This small-x regime of QCD is well described by an effective theory known as the Color Glass Condensate (CGC). In this thesis, we introduce the CGC and apply it to two different problems. First, we use the CGC to study forward heavy-quark production in pA collisions. When the quarks are nearly back-to-back, the CGC result coincides with the one in the TMD factorization approach. This allows us to extract the small-x limit of the Weizsäcker-Williams gluon distribution, as well as the dipole distribution and one extra gluon TMD. Each of these gluon TMDs is accompanied by a partner, which couples via the quark mass and which describes the linearly polarized gluon content of the unpolarized nucleus. We calculate the six resulting gluon TMDs analytically in the MV model, and evolve them in rapidity using a numerical implementation of JIMWLK. The second problem is situated within heavy-ion physics. Jets, produced in the scattering of two nuclei, travel through the Quark-Gluon Plasma (QGP) before reaching the detector, and are attenuated as a result of their interaction with this medium. This phenomenon, known as jet quenching, is one of the main probes to investigate the QGP. We focus on the transverse momentum broadening of a hard particle traveling through a nuclear medium, and employ small-x techniques to attempt to resum the leading logarithmic corrections due to soft gluon radiation. Although, ultimately, we can only solve the resulting in-medium evolution equation to DLA accuracy, we do present a concise framework for the problem, and draw a detailed comparison with the CGC and with the literature.
Michal Czakon🇩🇪 · David Heymes🇬🇧 · Alexander Mitov🇬🇧 · Davide Pagani🇩🇪 · Ioannis Tsinikos🇧🇪 · Marco Zaro🇳🇱
We provide the most up-to-date predictions for the top-quark charge asymmetry A_C at the LHC with a centre-of-mass energy of 8 TeV. Our result is accurate at the NNLO level in the strong interactions and at the complete-NLO level in both the strong and electroweak interactions. We present results for the inclusive A_C, several differential asymmetries as well as the P_{T,tt} and M_{tt} cumulative asymmetries. Similarly to the Tevatron forward-backward asymmetry A_FB, both NNLO QCD and NLO EW corrections to A_C are found to be significant. The inclusion of higher-order corrections reduces the residual scale dependence in the predicted A_C. The pattern of higher-order corrections indicates good perturbative control over these observables. We conclude that at present there is nearly uniform agreement between Standard Model predictions and LHC measurements across all A_C-related observables. All previously published differential A_FB predictions at the Tevatron are updated to the same accuracy.
Stefano Di Vita🇮🇹 · Gauthier Durieux🇩🇪 · Christophe Grojean🇩🇪 · Jiayin Gu🇨🇳 · Zhen Liu🇺🇸 · Giuliano Panico🇪🇸 · Marc Riembau🇪🇸 · Thibaud Vantalon🇩🇪
We perform a global effective-field-theory analysis to assess the precision on the determination of the Higgs trilinear self-coupling at future lepton colliders. Two main scenarios are considered, depending on whether the center-of-mass energy of the colliders is sufficient or not to access Higgs pair production processes. Low-energy machines allow for ~40% precision on the extraction of the Higgs trilinear coupling through the exploitation of next-to-leading-order effects in single Higgs measurements, provided that runs at both 240/250 GeV and 350 GeV are available with luminosities in the few attobarns range. A global fit, including possible deviations in other SM couplings, is essential in this case to obtain a robust determination of the Higgs self-coupling. High-energy machines can easily achieve a ~20% precision through Higgs pair production processes. In this case, the impact of additional coupling modifications is milder, although not completely negligible.
A.B. Balantekin (Wisconsin U., Madison)🇺🇸
Different approaches to the calculation of neutrino-nucleus cross sections are summarized. Potential impact of improving the nuclear physics input into neutrino interactions and cross section calculations on uncovering new physics is discussed using the example of reactor anomaly. Importance of a thorough understanding of neutrino interactions in astrophysics and cosmology is highlighted.
Yevgeny V. Stadnik
The exchange of a pair of low-mass neutrinos between electrons, protons and neutrons produces a "long-range" potential, which can be sought for in phenomena originating on the atomic and sub-atomic length scales. We calculate the effects of neutrino-pair exchange on transition and binding energies in atoms and nuclei. In the case of atomic s-wave states, there is a large enhancement of the induced energy shifts due to the lack of a centrifugal barrier and the highly singular nature of the neutrino-mediated potential. We derive limits on neutrino-mediated forces from measurements of the deuteron binding energy and transition energies in positronium, muonium, hydrogen and deuterium, as well as isotope-shift measurements in calcium ions. Our limits improve on existing constraints on neutrino-mediated forces from experiments that search for new macroscopic forces by 18 orders of magnitude. Future spectroscopy experiments have the potential to probe long-range forces mediated by the exchange of pairs of standard-model neutrinos and other weakly-charged particles.
Golam Sarwar🇮🇳 · Sushant K. Singh🇮🇳 · Jan-e Alam🇮🇳
The power spectrum of fluctuations in the momentum distributions of particles have been estimated with optical Glauber and Monte-Carlo Glauber initial conditions for relativistic heavy ion collisions. The evaluation procedure adopted in this work is analogous to the one used in the calculation of power spectrum in Cosmic Microwave Background Radiation (CMBR). The power spectrum due to perturbations in the phase space distribution of the particles has also been evaluated. The perturbation in phase space has been evolved through the Boltzmann transport equation in an expanding quark gluon plasma (QGP) background. The expansion of the QGP has been treated within the purview of (3+1) dimensional relativistic hydrodynamics. We observe that the non-equlibrium effects introduced as perturbations in the phase space distributions can be traced from the enhancement of the power spectrum as well as through its variation with temperature which is distinctly different from the case of vanishing perturbation. A relation has been derived between the power spectrum and the flow harmonics.
Andrés Luna🇬🇧 · Isobel Nicholson🇬🇧 · Donal O'Connell🇬🇧 · Chris D. White🇬🇧
We explain how the lowest-order classical gravitational radiation produced during the inelastic scattering of two Schwarzschild black holes in General Relativity can be obtained from a tree scattering amplitude in gauge theory coupled to scalar fields. The gauge calculation is related to gravity through the double copy. We remove unwanted scalar forces which can occur in the double copy by introducing a massless scalar in the gauge theory, which is treated as a ghost in the link to gravity. We hope these methods are a step towards a direct application of the double copy at higher orders in classical perturbation theory, with the potential to greatly streamline gravity calculations for phenomenological applications.
Tamas G. Kovacs (Debrecen, Inst. Nucl. Res.)🇭🇺
We recently obtained an estimate of the axion mass based on the hypothesis that axions make up most of the dark matter in the universe. A key ingredient for this calculation was the temperature-dependence of the topological susceptibility of full QCD. Here we summarize the calculation of the susceptibility in a range of temperatures from well below the finite temperature cross-over to around 2 GeV. The two main difficulties of the calculation are the unexpectedly slow convergence of the susceptibility to its continuum limit and the poor sampling of nonzero topological sectors at high temperature. We discuss how these problems can be solved by two new techniques, the first one with reweighting using the quark zero modes and the second one with the integration method.
A. Ayriyan🇷🇺 · N.-U. Bastian🇵🇱 · D. Blaschke🇷🇺 · H. Grigorian🇷🇺 · K. Maslov🇷🇺 · D. N. Voskresensky🇷🇺
We investigate the robustness of third family solutions for hybrid compact stars with a quark matter core that correspond to the occurrence of high-mass twin stars against a softening of the phase transition by means of a construction that mimics the effects of pasta structures in the mixed phase. We consider a class of hybrid equations of state that exploits a relativistic mean-field model for the hadronic as well as for the quark matter phase. We present parametrizations that correspond to branches of high-mass twin star pairs with maximum masses between and having radius differences between 3.2 km and 1.5 km, respectively. When compared to a Maxwell construction with a fixed value of critical pressure the effect of the mixed phase construction consists in the occurrence of a region of pressures around belonging to the coexistence of hadronic and quark matter phases between the onset pressure at and the end of the transition at . The maximum broadening which would still allow mass twin compact stars is found to be for all parametrizations within the present class of models. At least the heavier of the neutron stars of the binary merger GW170817 could have been a member of the third family of hybrid stars.
D. F. Jackson Kimball🇺🇸 · S. Afach🇩🇪 · D. Aybas🇺🇸 · J. W. Blanchard🇩🇪 · D. Budker🇩🇪 · G. Centers🇩🇪 · M. Engler🇩🇪 · N. L. Figueroa🇩🇪 · A. Garcon🇩🇪 · P. W. Graham🇺🇸 · H. Luo🇨🇳 · S. Rajendran🇺🇸 and 6 other authors
An overview of our experimental program to search for axion and axion-like-particle (ALP) dark matter using nuclear magnetic resonance (NMR) techniques is presented. An oscillating axion field can exert a time-varying torque on nuclear spins either directly or via generation of an oscillating nuclear electric dipole moment (EDM). Magnetic resonance techniques can be used to detect such an effect. The first-stage experiments explore many decades of ALP parameter space beyond the current astrophysical and laboratory bounds. It is anticipated that future versions of the experiments will be sensitive to the axions associated with quantum chromodynamics (QCD) having masses .
* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.