Thu·Apr 20, 2017Thursday·April 20, 2017

1. 01*

   Constraints on top quark non-standard interactions from Higgs and $t\bar{t}$ production cross sections

   D. Barducci🇮🇹 · M. Fabbrichesi🇮🇹 · A. Tonero🇧🇷

   We identify the differential cross sections for $t\bar{t}$ production and the total cross section for Higgs production through gluon fusion as the processes in which the two effective operators describing the leading non-standard interactions of the top quark with the gluon can be disentangled and studied in an independent fashion. Current data on the Higgs production and the $\mathrm{d}\sigma /\mathrm{d}{p}_T^t$ differential cross section provide limits comparable, but not more stringent, than those from the total $t\bar{t}$ cross sections measurements at the LHC and Tevatron, where however the two operators enter on the same footing and can only be constrained together. Given the present uncertainties, we find that the most stringent bounds are provided by a combination of data on the $t\bar{t}$ total cross sections together with those from the Higgs production. We conclude by stating the (modest) reduction in the uncertainties necessary to provide more stringent limits by means of the Higgs production and $t\bar{t}$ differential cross section observables at the LHC with the future luminosity of 300 and 3000 fb${}^{-1}$.

   hep-phPRD(2017)·14 citations
2. 02*

   Charge asymmetry from CP-violating fermion scattering off bubble walls during the electroweak phase transition

   Alejandro Ayala🇲🇽 · L. A. Hernández🇲🇽 · Jordi Salinas🇲🇽

   We compute the net electric current generated during a first order electroweak phase transition when fermions transit from the false to the true vacuum. This current is generated by the CP-violating fermion interaction with the Higgs during the phase transition and is quantified in terms of a CP-violating phase in the bubble wall separating the symmetric from the symmetry-broken phases. We comment on the seed magnetic field that this current is able to generate and it is possible implications for magnetogenesis in the early universe during the electroweak phase transition.

   hep-phPRD(2017)·4 citations
3. 03*

   Dynamical vs. equilibrium properties of the QCD phase transition: a holographic perspective

   Romulo Rougemont (IIP, Brazil)🇧🇷 · Renato Critelli (Sao Paulo U.)🇧🇷 · Jacquelyn Noronha-Hostler (Houston U.)🇺🇸 · Jorge Noronha (Sao Paulo U.)🇧🇷 · Claudia Ratti (Houston U.)🇺🇸

   We employ an Einstein-Maxwell-Dilaton (EMD) holographic model, which is known to be in good agreement with lattice results for the QCD equation of state with $(2+1)$ flavors and physical quark masses, to investigate the temperature and baryon chemical potential dependence of the susceptibilities, conductivities, and diffusion coefficients associated with baryon, electric, and strangeness conserved charges. We also determine how the bulk and shear viscosities of the plasma vary in the plane of temperature and baryon chemical potential. The diffusion of conserved charges and the hydrodynamic viscosities in a baryon rich quark-gluon plasma are found to be suppressed with respect to the zero net baryon case. The transition temperatures associated with equilibrium and non-equilibrium quantities are determined as a function of the baryon chemical potential for the first time. Because of the crossover nature of the QCD phase transition even at moderately large values of the chemical potential, we find that the transition temperatures associated with different quantities are spread in the interval between $130-200$ MeV and they all decrease with increasing baryon chemical potential.

   hep-phhep-thnucl-exnucl-thPRD(2017)·119 citations
4. 04*

   Naturalness, dark matter, and the muon anomalous magnetic moment in supersymmetric extensions of the standard model with a pseudo-Dirac gluino

   Chuang Li🇨🇳 · Bin Zhu🇨🇳 · Tianjun Li🇨🇳

   We study the naturalness, dark matter, and muon anomalous magnetic moment in the Supersymmetric Standard Models (SSMs) with a pseudo-Dirac gluino (PDGSSMs) from hybrid $F-$ and $D-$term supersymmetry (SUSY) breakings. To obtain the observed dark matter relic density and explain the muon anomalous magnetic moment, we find that the low energy fine-tuning measures are larger than about 30 due to strong constraints from the LUX and PANDAX experiments. Thus, to study the natural PDGSSMs, we consider multi-component dark matter and then the relic density of the lighest supersymmetric particle (LSP) neutralino is smaller than the correct value. We classify our models into six kinds: (i) Case A is a general case, which has small low energy fine-tuning measure and can explain the anomalous magnetic moment of the muon; (ii) Case B with the LSP neutralino and light stau coannihilation; (iii) Case C with Higgs funnel; (iv) Case D with Higgsino LSP; (v) Case E with light stau coannihilation and Higgsino LSP; (vi) Case F with Higgs funnel and Higgsino LSP. We study these Cases in details, and show that our models can be natural and consistent with the LUX and PANDAX experiments, as well as explain the muon anomalous magnetic moment. In particular, all these cases except the stau coannihilation can even have low energy fine-tuning measures around 10.

   hep-phNPB(2018)·10 citations
5. 05*

   Gauge-invariant implications of the LHCb measurements on Lepton-Flavour Non-Universality

   Alejandro Celis🇩🇪 · Javier Fuentes-Martin🇪🇸 · Avelino Vicente🇪🇸 · Javier Virto🇨🇭

   We study the implications of the recent measurements of $R_K$ and $R_{K^{\ast }}$ by the LHCb collaboration. We do that by adopting a model-independent approach based on the Standard Model Effective Field Theory (SMEFT), in which the dominant new physics effects are encoded in the coefficients of dimension-six operators respecting the full Standard Model (SM) gauge symmetry. After providing simplified expressions for $R_K$ and $R_{K^{\ast }}$, we determine the implications of the recent LHCb results for these observables on the coefficients of the SMEFT operators at low and high energies. We also take into account all $b\to s\ell \ell$ data, which combined lead to effective New Physics (NP) scenarios with SM pulls in excess of 5~$\sigma$. Thus the operators discussed in this paper would be the first dimension-six terms in the SM Lagrangian to be detected experimentally. Indirect constraints on these operators are also discussed. The results of this paper transcend the singularity of the present situation, and set a standard for future analyses in $b\to s$ transitions when the NP is assumed to lie above the electroweak scale.

   hep-phPRD(2017)·127 citations
6. 06*

   Higgs boson pair production at NNLO in QCD including dimension 6 operators

   Daniel de Florian🇦🇷 · Ignacio Fabre🇦🇷 · Javier Mazzitelli🇨🇭

   In this paper, we present the computation of the Higgs boson pair production cross section, both inclusive as well as differential on the invariant mass distribution, at next-to-next-to-leading order (NNLO) in QCD including effects of new physics beyond the standard model. We parametrize the effects of new physics with the relevant dimension 6 operators in a standard model effective field theory (EFT) approach and examine their phenomenology. The dependence of the NNLO $K$-factor on the EFT couplings is analysed, finding that, while rather flat for a number of EFT coefficients, it can considerably differ from the standard model value in some particular regions of the parameter space. We present explicit examples of (almost) degeneracy in the NNLO cross-section with respect to the anomalous couplings, showing that the invariant mass distribution has a much larger sensitivity to phenomena beyond the standard model and can be used as a tool to discriminate their effect.

   hep-phJHEP(2017)·52 citations
7. 07*

   Role of the $N^{\ast }(1535)$ in the ${\Lambda }_c^{+}\to {\bar{K}}^0\eta p$ decay

   Ju-Jun Xie🇨🇳 · Li-Sheng Geng🇨🇳

   The nonleptonic weak decay of ${\Lambda }_c^{+}\to {\bar{K}}^0\eta p$ is analyzed from the viewpoint of probing the $N^{\ast }(1535)$ resonance, which has a big decay branching ratio to $\eta N$. Up to an arbitrary normalization, the invariant mass distribution of $\eta p$ is calculated with both the chiral unitary approach and an effective Lagrangian model. Within the chiral unitary approach, the $N^{\ast }(1535)$ resonance is dynamically generated from the final state interaction of mesons and baryons in the strangeness zero sector. For the effective Lagrangian model, we take a Breit-Wigner formula to describe the distribution of the $N^{\ast }(1535)$ resonance. It is found that the behavior of the $N^{\ast }(1535)$ resonance in the ${\Lambda }_c^{+}\to {\bar{K}}^0{N}^{\ast }(1535)\to {\bar{K}}^0\eta p$ decay within the two approaches is different. The proposed ${\Lambda }_c^{+}$ decay mechanism can provide valuable information on the properties of the $N^{\ast }(1535)$ and can in principle be tested by facilities such as BEPC II and SuperKEKB.

   hep-phPRD(2017)·25 citations
8. 08*

   Breit-Wigner distribution, quantum beats and GSI Anomaly

   M. S. Hosseini🇮🇷 · S. A. Alavi🇮🇷

   The relationship between Breit-Wigner distribution as an underlying basis for decaying unstable quantum systems and GSI experiment (anomaly) has not been addressed properly in the literatures. We show that quantum beats can be obtained using a superposition of two Breit-Wigner distributions. This modified distribution can explain the GSI time anomaly with quantum beats resulting from the existence of two energy levels of the decaying ion.

   hep-phnucl-thquant-phAnnals Phys.(2019)·1 citation
9. 09*

   On the large-Q^2 behavior of the pion transition form factor

   Gernot Eichmann🇩🇪 · Christian S. Fischer🇩🇪 · Esther Weil🇩🇪 · Richard Williams🇩🇪

   We study the transition of non-perturbative to perturbative QCD in situations with possible violations of scaling limits. To this end we consider the singly- and doubly-virtual pion transition form factor ${\pi }^0\to \gamma \gamma$ at all momentum scales of symmetric and asymmetric photon momenta within the Dyson-Schwinger/Bethe-Salpeter approach. For the doubly virtual form factor we find good agreement with perturbative asymptotic scaling laws. For the singly-virtual form factor our results agree with the Belle data. At very large off-shell photon momenta we identify a mechanism that introduces quantitative modifications to Efremov-Radyushkin-Brodsky-Lepage scaling.

   hep-phhep-latnucl-thPLB(2017)·49 citations
10. 10*

    Automation of NLO QCD and EW corrections with Sherpa and Recola

    Benedikt Biedermann🇩🇪 · Stephan Bräuer🇩🇪 · Ansgar Denner🇩🇪 · Mathieu Pellen🇩🇪 · Steffen Schumann🇩🇪 · Jennifer M. Thompson🇩🇪

    This publication presents the combination of the one-loop matrix-element generator Recola with the multipurpose Monte Carlo program Sherpa. Since both programs are highly automated, the resulting Sherpa+Recola framework allows for the computation of -in principle- any Standard Model process at both NLO QCD and EW accuracy. To illustrate this, three representative LHC processes have been computed at NLO QCD and EW: vector-boson production in association with jets, off-shell Z-boson pair production, and the production of a top-quark pair in association with a Higgs boson. In addition to fixed-order computations, when considering QCD corrections, all functionalities of Sherpa, i.e. particle decays, QCD parton showers, hadronisation, underlying events, etc. can be used in combination with Recola. This is demonstrated by the merging and matching of one-loop QCD matrix elements for Drell-Yan production in association with jets to the parton shower. The implementation is fully automatised, thus making it a perfect tool for both experimentalists and theorists who want to use state-of-the-art predictions at NLO accuracy.

    hep-phhep-exEPJC(2017)·92 citations
11. 11*

    Tests for CPT sum rule and U-spin violation in Time-dependent CP violation of $B_s^0\to K^{+}{K}^{-}$ and $B_d^0\to {\pi }^{+}{\pi }^{-}$

    Xiao-Gang He🇨🇳 · Siao-Fong Li🇹🇼 · Bo Ren🇨🇳 · Xing-Bo Yuan🇹🇼

    Recent LHCb data for time-dependent CP violation in $B_d^0\to {\pi }^{+}{\pi }^{-}$ and $B_s^0\to K^{+}{K}^{-}$ show deviations from theoretical predictions. Besides their central values for ${\mathcal{C}}_{K^{+}{K}^{-}}$, ${\mathcal{S}}_{K^{+}{K}^{-}}$ and ${\mathcal{A}}_{K^{+}{K}^{-}}^{\Delta \Gamma }$ violate quantum mechanic CPT invariant sum rule (CPT sum rule) prediction of $|{\mathcal{C}}_{K^{+}{K}^{-}}{|}^2+|{\mathcal{S}}_{K^{+}{K}^{-}}{|}^2+|{\mathcal{A}}_{K^{+}{K}^{-}}^{\Delta \Gamma }{|}^2=1$ (LHCb data imply the sum to be $0.67\pm 0.20$.), their values for ${\mathcal{C}}_{K^{+}{K}^{-}}=0.24\pm 0.06\pm 0.02$ and ${\mathcal{C}}_{{\pi }^{+}{\pi }^{-}}=-0.24\pm 0.07\pm 0.01$ also show large violation of SU(3) or its U-spin sub-group symmetry (SU(3)/U) relation ${\mathcal{C}}_{K^{+}{K}^{-}}/{\mathcal{C}}_{{\pi }^{-}{\pi }^{+}}=-\mathcal{B}(B_d^0\to {\pi }^{-}{\pi }^{+}){\tau }_{B_s^0}/\mathcal{B}(B_s^0\to K^{+}{K}^{-}){\tau }_{B_d^0}$ (LHCb data imply the ratio of left-side to right-side to be $4.67\pm 1.88$.) . The LHCb results need to be further confirmed to be taken seriously. We suggest to use time-dependent CP violation in $B_s\to K^0{\bar{K}}^0,{\pi }^{+}{\pi }^{-},{\pi }^0{\pi }^0$ to further test the CPT sum rule. Assuming that the sum rule holds, we propose that violation of the SU(3)/U relation may indicate a large FSI phase difference in the ${\pi }^{+}{\pi }^{-}$ and $K^{+}{K}^{-}$ re-scattering. We suggest several other U-spin pairs of $B\to PP$ decays to further test SU(3)/U relations.

    hep-phhep-exPRD(2017)·7 citations
12. 12*

    Finite temperature QCD four-point function in the presence of a weak magnetic field within the hard thermal loop approximation

    Najmul Haque🇩🇪

    We compute the weak magnetic field correction to the four-point quark-gluon vertex at finite temperature and chemical potential within the hard thermal loop approximation. The resulting four-point quark-gluon vertex satisfies the Ward identity with the three-point quark-gluon vertex.

    hep-phPRD(2017)·12 citations
13. 13*

    A leptoquark model to accommodate $R_K^{\exp }<R_K^{\mathrm{SM}}$ and $R_{K^{\ast }}^{\exp }<R_{K^{\ast }}^{\mathrm{SM}}$

    Damir Bečirević🇫🇷 · Olcyr Sumensari🇫🇷

    We show that a modification of the model with a low energy scalar leptoquark state carrying hypercharge $Y=7/6$ allows to accommodate both $R_K<1$ and $R_{K^{\ast }}<1$, through loop effects, consistent with recent observations made at LHCb. We describe details of the model, compute the relevant Wilson coefficient and, after discussing a number of constraints, we examine the phenomenological consequences of the model. The bounds on the lepton flavor violating decay rates, induced by this model, include $\mathcal{B}(Z\to \mu \tau )\lesssim \mathcal{O}(10^{-7})$, and $\mathcal{B}(B\to K\mu \tau )\lesssim \mathcal{O}(10^{-9})$. We also comment on the interpretation of the bounds on the leptoquark mass obtained from the direct searches at LHC.

    hep-phJHEP(2017)·168 citations
14. 14*

    Jet Substructure Studies with CMS Open Data

    Aashish Tripathee🇺🇸 · Wei Xue🇺🇸 · Andrew Larkoski🇺🇸 · Simone Marzani🇺🇸 · Jesse Thaler🇺🇸

    We use public data from the CMS experiment to study the 2-prong substructure of jets. The CMS Open Data is based on 31.8/pb of 7 TeV proton-proton collisions recorded at the Large Hadron Collider in 2010, yielding a sample of 768,687 events containing a high-quality central jet with transverse momentum larger than 85 GeV. Using CMS's particle flow reconstruction algorithm to obtain jet constituents, we extract the 2-prong substructure of the leading jet using soft drop declustering. We find good agreement between results obtained from the CMS Open Data and those obtained from parton shower generators, and we also compare to analytic jet substructure calculations performed to modified leading-logarithmic accuracy. Although the 2010 CMS Open Data does not include simulated data to help estimate systematic uncertainties, we use track-only observables to validate these substructure studies.

    hep-phhep-exPRD(2017)·77 citations
15. 15*

    Non-resonant Collider Signatures of a Singlet-Driven Electroweak Phase Transition

    Chien-Yi Chen🇨🇦 · Jonathan Kozaczuk🇺🇸 · Ian M. Lewis🇺🇸

    We analyze the collider signatures of the real singlet extension of the Standard Model in regions consistent with a strong first-order electroweak phase transition and a singlet-like scalar heavier than the Standard Model-like Higgs. A definitive correlation exists between the strength of the phase transition and the trilinear coupling of the Higgs to two singlet-like scalars, and hence between the phase transition and non-resonant scalar pair production involving the singlet at colliders. We study the prospects for observing these processes at the LHC and a future 100 TeV $pp$ collider, focusing particularly on double singlet production. We also discuss correlations between the strength of the electroweak phase transition and other observables at hadron and future lepton colliders. Searches for non-resonant singlet-like scalar pair production at 100 TeV would provide a sensitive probe of the electroweak phase transition in this model, complementing resonant di-Higgs searches and precision measurements. Our study illustrates a strategy for systematically exploring the phenomenologically viable parameter space of this model, which we hope will be useful for future work.

    hep-phhep-exJHEP(2017)·119 citations
16. 16*

    Reconsidering the One Leptoquark solution: flavor anomalies and neutrino mass

    Yi Cai🇦🇺 · John Gargalionis🇦🇺 · Michael A. Schmidt🇦🇺 · Raymond R. Volkas🇦🇺

    We reconsider a model introducing a scalar leptoquark $\varphi \sim (3,1,-1/3)$ to explain recent deviations from the standard model in semileptonic $B$ decays. The leptoquark can accommodate the persistent tension in the decays $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$ as long as its mass is lower than approximately $10\text{ TeV}$, and we show that a sizeable Yukawa coupling to the right-chiral tau lepton is necessary for an acceptable explanation. Agreement with the measured $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$ rates is mildly compromised for parameter choices addressing the tensions in $b\to s\mu \mu$, where the model can significantly reduce the discrepancies in angular observables, branching ratios and the lepton-flavor-universality observables $R_K$ and $R_{K^{\ast }}$. The leptoquark can also reconcile the predicted and measured value of the anomalous magnetic moment of the muon and appears naturally in models of radiative neutrino mass derived from lepton-number violating effective operators. As a representative example, we incorporate the particle into an existing two-loop neutrino mass scenario derived from a dimension-nine operator. In this specific model, the structure of the neutrino mass matrix provides enough freedom to explain the small masses of the neutrinos in the region of parameter space dictated by agreement with the anomalies in $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$, but not the $b\to s$ transition. This is achieved without excessive fine-tuning in the parameters important for neutrino mass.

    hep-phJHEP(2017)·197 citations
17. 17*

    Cosmological Horizons, Uncertainty Principle and Maximum Length Quantum Mechanics

    L. Perivolaropoulos🇬🇷

    The cosmological particle horizon is the maximum measurable length in the Universe. The existence of such a maximum observable length scale implies a modification of the quantum uncertainty principle. Thus due to non-locality of quantum mechanics, the global properties of the Universe could produce a signature on the behaviour of local quantum systems. A Generalized Uncertainty Principle (GUP) that is consistent with the existence of such a maximum observable length scale $l_{max}$ is $\Delta x\Delta p\ge \frac{\hslash }{2}\frac{1}{1-\alpha \Delta x^2}$ where $\alpha =l_{max}^{-2}\simeq (H_0/c{)}^2$ ($H_0$ is the Hubble parameter and $c$ is the speed of light). In addition to the existence of a maximum measurable length $l_{max}=\frac{1}{\sqrt{\alpha }}$, this form of GUP implies also the existence of a minimum measurable momentum $p_{min}=\frac{3\sqrt{3}}{4}\hslash \sqrt{\alpha }$. Using appropriate representation of the position and momentum quantum operators we show that the spectrum of the one dimensional harmonic oscillator becomes ${\bar{\mathcal{E}}}_n=2n+1+{\lambda }_n\bar{\alpha }$ where ${\bar{\mathcal{E}}}_n\equiv 2E_n/\hslash \omega$ is the dimensionless properly normalized $n^{th}$ energy level, $\bar{\alpha }$ is a dimensionless parameter with $\bar{\alpha }\equiv \alpha \hslash /m\omega$ and ${\lambda }_n\sim n^2$ for $n\gg 1$ (we show the full form of ${\lambda }_n$ in the text). For a typical vibrating diatomic molecule and $l_{max}=c/H_0$ we find $\bar{\alpha }\sim 10^{-77}$ and therefore for such a system, this effect is beyond reach of current experiments. However, this effect could be more important in the early universe and could produce signatures in the primordial perturbation spectrum induced by quantum fluctuations of the inflaton field.

    ↳ gr-qcastro-ph.COhep-phhep-th+1PRD(2017)·58 citations
18. 18*

    From 4d Yang-Mills to 2d ${\mathbb{CP}}^{N-1}$ model: IR problem and confinement at weak coupling

    Masahito Yamazaki🇯🇵 · Kazuya Yonekura🇯🇵

    We study four-dimensional $\mathrm{SU}(N)$ Yang-Mills theory on $\mathbb{R}\times {\mathbb{T}}^3=\mathbb{R}\times S_A^1\times S_B^1\times S_C^1$, with a twisted boundary condition by a ${\mathbb{Z}}_N$ center symmetry imposed on $S_B^1\times S_C^1$. This setup has no IR zero modes and hence is free from IR divergences which could spoil trans-series expansion for physical observables. Moreover, we show that the center symmetry is preserved at weak coupling regime. This is shown by first reducing the theory on ${\mathbb{T}}^2=S_A\times S_B$, to connect the model to the two-dimensional ${\mathbb{CP}}^{N-1}$-model. Then, we prove that the twisted boundary condition by the center symmetry for the Yang-Mills is reduced to the twisted boundary condition by the ${\mathbb{Z}}_N$ global symmetry of ${\mathbb{CP}}^{N-1}$. There are $N$ classical vacua, and fractional instantons connecting those $N$ vacua dynamically restore the center symmetry. We also point out the presence of singularities on the Borel plane which depend on the shape of the compactification manifold, and comment on its implications.

    ↳ hep-thhep-lathep-phJHEP(2017)·70 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.