Mon·Jan 14, 2019Monday·January 14, 2019

1. 01*

   Interference Effects in $t\bar{t}$ Production at the LHC as a Window on New Physics

   Abdelhak Djouadi🇫🇷 · John Ellis🇬🇧 · Andrey Popov🇫🇷 · Jérémie Quevillon🇫🇷

   Many extensions of the Standard Model contain (pseudo)scalar bosons with masses in the TeV range. At hadron colliders, such particles would predominantly be produced in gluon fusion and would decay into top quark pair final sates, a signal that interferes with the large QCD background $gg\to t\bar{t}$. This phenomenon is of interest for searches for by the LHC experiments. Here, we consider the signal and background interference in this process and study it in various benchmark scenarios, including models with extra singlet (pseudo)scalar resonances, two-Higgs doublet models, and the minimal supersymmetric extension of the SM with parameters chosen to obtain the measured light Higgs mass (the hMSSM). We allow for the possible exchanges of beyond the SM vector-like particles as well as scalar quarks. We calculate the possible interference effects including realistic estimates of the attainable detection efficiency and mass resolution. Studies of our benchmark scenarios indicate that searches with an LHC detector could permit the observation of the $t\bar{t}$ final states or constrain significantly large regions of the parameter spaces of the benchmark scenarios.

   hep-phhep-exJHEP(2019)·50 citations
2. 02*

   The QCD NLO fragmentation functions for $c$ or $\bar{b}$ quark to $B_c$ or $B_c^{\ast }$ meson and their application

   Xu-Chang Zheng🇨🇳 · Chao-Hsi Chang🇨🇳 · Tai-Fu Feng🇨🇳 · Xing-Gang Wu🇨🇳

   The fragmentation functions for $c$ or $\bar{b}$ quark to $B_c$ or $B_c^{\ast }$ meson are derived up to QCD next-to-leading order (NLO). They are further computed numerically and presented in figures precisely. In order to reach a higher accuracy, we have also tried properly to apply them to estimating the $B_c$ and $B_c^{\ast }$ production at a $Z$-factory (an $e^{+}{e}^{-}$ collider running at the energy of the $Z$-boson pole).

   hep-phPRD(2019)·56 citations
3. 03*

   Effects of strong magnetic field on the formation of wakes in thermal QCD

   Mujeeb Hasan🇮🇳 · Binoy Krishna Patra🇮🇳

   We have investigated how the wakes in the induced charge density and in the potential due to the passage of highly energetic partons through a thermal QCD medium get affected by the presence of strong magnetic field. For that purpose, we wish to analyze first the dielectric responses of the medium both in presence and absence of strong magnetic field. We found that for slow moving partons, the real part of dielectric function is not affected by the magnetic field whereas for fast moving partons, for small $|\text{k}|$, it becomes very large and approaches towards its counterpart at $B=0$, for large $|\text{k}|$. On the other hand the imaginary part is decreased for both slow and fast moving partons, due to the fact that the imaginary contribution due to quark-loop vanishes. With these ingredients, we found that the oscillation in the (scaled) induced charge density, due to the very fast partons becomes less pronounced in the presence of strong magnetic field whereas for smaller parton velocity, no significant change is observed. For the (scaled) wake potential along the motion of fast moving partons (which is of Lennard-Jones (LJ) type), the depth of negative minimum in the backward region gets reduced drastically, resulting in the reduction of the amplitude of oscillation. On the other hand in the forward region, it remains as the screened Coulomb one, except the screening now becomes much stronger for higher parton velocity. Similarly for the wake potential transverse to the motion of partons in both forward and backward regions, the depth of LJ potential for fast moving partons gets decreased severely, but still retains the forward-backward symmetry. However, for lower parton velocity, the magnetic field does not affect it significantly.

   hep-phnucl-thInt.J.Mod.Phys.A(2021)·2 citations
4. 04*

   BasisGen: automatic generation of operator bases

   Juan Carlos Criado🇪🇸

   BasisGen is a Python package for the automatic generation of bases of operators in effective field theories. It accepts any semisimple symmetry group and fields in any of its finite dimensional irreducible representations. It takes into account integration by parts redundancy and, optionally, the use of equations of motion. The implementation is based in well-known methods to generate and decompose representations using roots and weights, which allow for fast calculations, even with large numbers of fields and high-dimensional operators. BasisGen can also be used to do some representation-theoretic operations, such as finding the weight system of an irreducible representation from its highest weight or decomposing a tensor product of representations.

   hep-phEPJC(2019)·60 citations
5. 05*

   Study of Unflavored Light Mesons with $J^{PC}=2^{--}$

   Dan Guo🇨🇳 · Cheng-Qun Pang🇨🇳 · Zhan-Wei Liu🇨🇳 · Xiang Liu🇨🇳

   The unflavored light meson families, namely ${\omega }_2$, ${\rho }_2$, and ${\varphi }_2$, are studied systematically by investigating the spectrum and the two-body strong decays allowed by Okubo-Zweig-Iizuka rule. Including the four experimentally observed states and other predicted states, phenomenological analysis of the partial decay widths can verify the corresponding assignments of these states into the families. Moreover, we provide typical branching ratios of the dominant decay channels, especially for missing ground states, which is helpful to search for or confirm them and explore more properties of these families at experiment.

   hep-phPRD(2019)·21 citations
6. 06*

   Pentaquarks with anticharm or beauty revisited

   J.-M. Richard🇫🇷 · A. Valcarce🇪🇸 · J. Vijande🇪🇸

   We use a constituent model to analyze the stability of pentaquark $\bar{Q}qqqq$ configurations with a heavy antiquark $\bar{c}$ or $\bar{b}$, and four light quarks $uuds$, $ddsu$ or $ssud$. The interplay between chromoelectric and chromomagnetic effects is not favorable, and, as a consequence, no bound state is found below the lowest dissociation threshold.

   hep-phPLB(2019)·17 citations
7. 07*

   Progress and challenges in the study of direct CP violation and $\gamma$ determinations: summary of CKM 2018 working group V

   K. Keri Vos🇩🇪 · Martin Sevior🇦🇺 · Stefano Perazzini🇨🇭

   In the study of CP violation within and beyond the Standard Model of particle physics, pure hadronic B decays are the key players. Improving the determination of the CKM angle $\gamma$ is one of the important tasks in this endeavour. Besides, the full description of pure hadronic decays due to their strong interaction dynamics remains one of the challenges. In this summary, we discuss the recent results and progress on $\gamma$ determinations and direct CP violation in pure hadronic B decays as presented at CKM 2018.

   hep-phhep-ex1 citation
8. 08*

   The Lightest Higgs Boson Mass of the MSSM at Three-Loop Accuracy

   E. A. Reyes R.🇨🇴 · A. R. Fazio🇨🇴

   In this article we provide explicit computations of the quantum corrections to the lightest CP-even Higgs Boson mass in the real version of the Minimal Supersymmetric Standard Model. We compute the contributions coming from the SUSY-QCD sector with a precision of three loops at order $O({\alpha }_t{\alpha }_s^2)$. The renormalization procedure adopted is based on the dimensional reduction scheme in order to preserve supersymmetry to all perturbative orders. The calculation extends the region of validity of previous studies to the whole supersymmetric parameter space. The involved master integrals have been computed by exploiting new proposed approaches based on the dispersion relation techniques for the numerical calculation of three-loop vacuum integrals with arbitrary mass scales.

   hep-phNPB(2019)·21 citations
9. 09*

   Towards Quasi-Transverse Momentum Dependent PDFs Computable on the Lattice

   Markus A. Ebert🇺🇸 · Iain W. Stewart🇺🇸 · Yong Zhao🇺🇸

   Transverse momentum dependent parton distributions (TMDPDFs) which appear in factorized cross sections involve infinite Wilson lines with edges on or close to the light-cone. Since these TMDPDFs are not directly calculable with a Euclidean path integral in lattice QCD, we study the construction of quasi-TMDPDFs with finite-length spacelike Wilson lines that are amenable to such calculations. We define an infrared consistency test to determine which quasi-TMDPDF definitions are related to the TMDPDF, by carrying out a one-loop study of infrared logarithms of transverse position $b_T\sim {\Lambda }_{\mathrm{QCD}}^{-1}$, which must agree between them. This agreement is a necessary condition for the two quantities to be related by perturbative matching. TMDPDFs necessarily involve combining a hadron matrix element, which nominally depends on a single light-cone direction, with soft matrix elements that necessarily depend on two light-cone directions. We show at one loop that the simplest definitions of the quasi hadron matrix element, the quasi soft matrix element, and the resulting quasi-TMDPDF all fail the infrared consistency test. Ratios of impact parameter quasi-TMDPDFs still provide nontrivial information about the TMDPDFs, and are more robust since the soft matrix elements cancel. We show at one loop that such quasi ratios can be matched to ratios of the corresponding TMDPDFs. We also introduce a modified "bent" quasi soft matrix element which yields a quasi-TMDPDF that passes the consistency test with the TMDPDF at one loop, and discuss potential issues at higher orders.

   hep-phJHEP(2019)·135 citations
10. 10*

    Matter dependence of the four-loop cusp anomalous dimension

    Johannes M. Henn🇩🇪 · Tiziano Peraro🇨🇭 · Maximilian Stahlhofen🇩🇪 · Pascal Wasser🇩🇪

    We compute analytically the matter-dependent contributions to the quartic Casimir term of the four-loop light-like cusp anomalous dimension in QCD, with $n_f$ fermion and $n_s$ scalar flavours. The result is extracted from the double pole of a scalar form factor. We adopt a new strategy for the choice of master integrals with simple analytic and infrared properties, which significantly simplifies our calculation. To this end we first identify a set of integrals whose integrands have a dlog form, and are hence expected to have uniform transcendental weight. We then perform a systematic analysis of the soft and collinear regions of loop integration and build linear combinations of integrals with a simpler infrared pole structure. In this way, only integrals with ten or fewer propagators are needed for obtaining the cusp anomalous dimension. These integrals are then computed via the method of differential equations through the addition of an auxiliary scale. Combining our result with that of a parallel paper, we obtain the complete $n_f$ dependence of the four-loop cusp anomalous dimension in QCD. Finally, using known numerical results for the gluonic contributions, we obtain an improved numerical prediction for the cusp anomalous dimension in $\mathcal{N}=4$ super Yang-Mills theory.

    hep-phhep-thPRL(2019)·100 citations
11. 11*

    Hunting for Vectorlike Quarks

    Radovan Dermisek🇺🇸 · Enrico Lunghi🇺🇸 · Seodong Shin🇺🇸

    We analyze decays of vectorlike quarks in extensions of the standard model and a two Higgs doublet model. We identify several typical patterns of branching ratios of the lightest new up-type quark, $t_4$, and down-type quark, $b_4$, depending on the structure of Yukawa couplings that mix the vectorlike and standard model quarks (we assume only mixing with the third generation) and also on their doublet or singlet nature. We find that decays into heavy neutral or charged Higgs bosons, when kinematically open, can easily dominate and even be close to 100\%: $b_4\to Hb$ at medium to large $\tan \beta$, $t_4\to Ht$ at small $\tan \beta$ and $b_4\to H^{\pm }t$, $t_4\to H^{\pm }b$ at both large and small $\tan \beta$. The pair production of vectorlike quarks leads to $6t$, $4t2b$, $2t4b$ and $6b$ final states. The decay modes into $W$, $Z$ and $h$ follow the pattern expected from the Goldstone boson equivalence limit that we generalize to scenarios with all possible couplings. We also discuss in detail the structure of Yukawa couplings required to significantly deviate from the pattern characteristic of the Goldstone boson equivalence limit that can result in essentially arbitrary branching ratios.

    hep-phJHEP(2019)·43 citations
12. 12*

    BubbleProfiler: finding the field profile and action for cosmological phase transitions

    Peter Athron (Monash U.)🇦🇺 · Csaba Balázs (Monash U.)🇦🇺 · Michael Bardsley (Monash U.)🇦🇺 · Andrew Fowlie (Nanjing Normal U. and Monash U.)🇦🇺 · Dylan Harries (Charles U. and Adelaide U.)🇦🇺 · Graham White (TRIUMF and Monash U.)🇨🇦

    We present BubbleProfiler, a C++ software package for finding field profiles in bubble walls and calculating the bounce action during phase transitions involving multiple scalar fields. Our code uses a recently proposed perturbative method for potentials with multiple fields and a shooting method for single field cases. BubbleProfiler is constructed with modularity, flexibility and practicality in mind. These principles extend from the input of an arbitrary potential with multiple scalar fields in various forms, through the code structure, to the testing suite. After reviewing the physics context, we describe how the methods are implemented in BubbleProfiler, provide an overview of the code structure and detail usage scenarios. We present a number of examples that serve as test cases of BubbleProfiler and comparisons to existing public codes with similar functionality. We also show a physics application of BubbleProfiler in the scalar singlet extension of the Standard Model of particle physics by calculating the action as a function of model parameters during the electroweak phase transition. BubbleProfiler completes an important link in the toolchain for studying the properties of the thermal phase transition driving baryogenesis and properties of gravitational waves in models with multiple scalar fields. The code can be obtained from: https://github.com/bubbleprofiler/bubbleprofiler

    hep-phastro-ph.COComput.Phys.Commun.(2019)·84 citations
13. 13*

    Dual MeV Gamma-Ray and Dark Matter Observatory -- GRAMS Project

    Tsuguo Aramaki🇺🇸 · Per Hansson Adrian🇺🇸 · Georgia Karagiorgi🇺🇸 · Hirokazu Odaka🇯🇵

    GRAMS (Gamma-Ray and AntiMatter Survey) is a novel project that can simultaneously target both astrophysical observations with MeV gamma rays and an indirect dark matter search with antimatter. The GRAMS instrument is designed with a cost-effective, large-scale LArTPC (Liquid Argon Time Projection Chamber) detector surrounded by plastic scintillators. The astrophysical observations at MeV energies have not yet been well-explored (the so-called "MeV-gap") and GRAMS can improve the sensitivity by more than an order of magnitude compared to previous experiments. While primarily focusing on MeV gamma-ray observations, GRAMS is also optimized for cosmic ray antimatter surveys to indirectly search for dark matter. In particular, low-energy antideuterons will provide an essentially background-free dark matter signature. GRAMS will be a next generation experiment beyond the current GAPS (General AntiParticle Spectrometer) project for antimatter survey.

    ↳ astro-ph.HEhep-exhep-phAstropart.Phys.(2020)·122 citations
14. 14*

    Statistical properties of the repeating fast radio burst source FRB 121102

    Bing Li🇨🇳 · Long-Biao Li🇨🇳 · Zhi-Bin Zhang🇨🇳 · Jin-Jun Geng🇨🇳 · Li-Ming Song🇨🇳 · Yong-Feng Huang🇨🇳 · Yuan-Pei Yang🇨🇳

    Currently, FRB 121102 is the only fast radio burst source that was observed to give out bursts repeatedly. It shows a high repeating rate, with more than one hundred bursts being spotted, but with no obvious periodicity in the activities. Thanks to its repetition, the source was well localized with a subarcsecond accuracy, leading to a redshift measurement of about 0.2. FRB 121102 is a unique source that can help us understand the enigmatic nature of fast radio bursts. In this study, we analyze the characteristics of the waiting times between bursts from FRB 121102. It is found that there is a clear bimodal distribution for the waiting times. While most waiting times cluster at several hundred seconds, a small portion of the waiting times are strikingly in the range of 2--40 millisecond. More interestingly, it is found that the waiting time does not correlate with the burst intensity, either for the preceding burst or for the subsequent burst. It strongly indicates that the repeating bursts should be generated by some external mechanisms, but not internal mechanisms. As a result, the models involving collisions between small bodies and neutron stars could be competitive mechanisms for this interesting source.

    ↳ astro-ph.HEhep-phInt J Cosmol Astron Astrophys. 2019; 1(1)…·21 citations
15. 15*

    Importance of the Volume Fluctuation Correction on Higher Order Cumulants

    Tetsuro Sugiura🇯🇵

    Initial volume fluctuation (VF) caused by participant fluctuation would be the background which should be subtracted from experimentally measured higher-order cumulants. STAR experiment has been applied Centrality Bin Width Correction (CBWC) to suppress VF. However, CBWC is not perfect method, there might be thus residual fractions of VF backgrounds. Recently, Volume Fluctuation Correction (VFC) was developed under the assumption of the independent particle production (IPP) model. In this talk, the importance of subtracting VF and validity of the VFC are studied by using simple toy models assuming IPP as well as UrQMD model. The results showed that VFC worked well in toy model but did not work well in UrQMD which imply that IPP model could be broken in UrQMD.

    ↳ nucl-exhep-exhep-phJPS Conf.Proc.(2019)·0 citations
16. 16*

    Dark Disk Substructure and Superfluid Dark Matter

    Stephon Alexander🇺🇸 · Jason J. Bramburger🇺🇸 · Evan McDonough🇺🇸

    Dark matter substructure has the potential to discriminate between broad classes of dark matter models. With this in mind, we construct novel solutions to the equations of motion governing condensate dark matter candidates, namely axion Bose-Einstein condensates and superfluids. These solutions are highly compressed along one axis and thus have a disk-like geometry. We discuss linear stability of these solutions, consider the astrophysical implications as a large-scale dark disk or as small scale substructure, and find a characteristic signal in strong gravitational lensing. This adds to the growing body of work that indicates that the morphology of dark matter substructure is a powerful probe of the nature of dark matter.

    ↳ astro-ph.COastro-ph.GAgr-qchep-ph+1PLB(2019)·33 citations
17. 17*

    FASER: ForwArd Search ExpeRiment at the LHC

    FASER Collaboration: Akitaka Ariga🇨🇭 · Tomoko Ariga🇨🇭 · Jamie Boyd🇨🇭 · Franck Cadoux🇨🇭 · David W. Casper🇺🇸 · Yannick Favre🇨🇭 · Jonathan L. Feng🇺🇸 · Didier Ferrere🇨🇭 · Iftah Galon🇺🇸 · Sergio Gonzalez-Sevilla🇨🇭 · Shih-Chieh Hsu🇺🇸 · Giuseppe Iacobucci🇨🇭 and 15 other authors

    FASER, the ForwArd Search ExpeRiment, is a proposed experiment dedicated to searching for light, extremely weakly-interacting particles at the LHC. Such particles may be produced in the LHC's high-energy collisions in large numbers in the far-forward region and then travel long distances through concrete and rock without interacting. They may then decay to visible particles in FASER, which is placed 480 m downstream of the ATLAS interaction point. In this work, we describe the FASER program. In its first stage, FASER is an extremely compact and inexpensive detector, sensitive to decays in a cylindrical region of radius R = 10 cm and length L = 1.5 m. FASER is planned to be constructed and installed in Long Shutdown 2 and will collect data during Run 3 of the 14 TeV LHC from 2021-23. If FASER is successful, FASER 2, a much larger successor with roughly R ~ 1 m and L ~ 5 m, could be constructed in Long Shutdown 3 and collect data during the HL-LHC era from 2026-35. FASER and FASER 2 have the potential to discover dark photons, dark Higgs bosons, heavy neutral leptons, axion-like particles, and many other long-lived particles, as well as provide new information about neutrinos, with potentially far-ranging implications for particle physics and cosmology. We describe the current status, anticipated challenges, and discovery prospects of the FASER program.

    ↳ hep-exhep-phphysics.ins-det162 citations

* 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.