Tue·Mar 28, 2017Tuesday·March 28, 2017

1. 01*

   Standard Model Parton Distributions at Very High Energies

   Christian W. Bauer🇺🇸 · Nicolas Ferland🇺🇸 · Bryan R.Webber🇬🇧

   We compute the leading-order evolution of parton distribution functions for all the Standard Model fermions and bosons up to energy scales far above the electroweak scale, where electroweak symmetry is restored. Our results include the 52 PDFs of the unpolarized proton, evolving according to the SU(3), SU(2), U(1), mixed SU(2) x U(1) and Yukawa interactions. We illustrate the numerical effects on parton distributions at large energies, and show that this can lead to important corrections to parton luminosities at a future 100 TeV collider.

   hep-phhep-exJHEP(2017)·87 citations
2. 02*

   Collinear factorization violation and effective field theory

   Matthew D. Schwartz🇺🇸 · Kai Yan🇺🇸 · Hua Xing Zhu🇺🇸

   The factorization of amplitudes into hard, soft and collinear parts is known to be violated in situations where incoming particles are collinear to outgoing ones. This result was first derived by studying limits where non-collinear particles become collinear. We show that through an effective field theory framework with Glauber operators, these factorization-violating effects can be reproduced from an amplitude that is factorized before the splitting occurs. We confirm results at one-loop, through single Glauber exchange, and at two-loops, through double Glauber exchange. To approach the calculation, we begin by reviewing the importance of Glauber scaling for factorization. We show that for any situation where initial state and final state particles are not collinear, the Glauber contribution is entirely contained in the soft contribution. The contributions coming from Glauber operators are necessarily non-analytic functions of external momentum, with the non-analyticity arising from the rapidity regulator. The non-analyticity is critical so that Glauber operators can both preserve factorization when it holds and produce factorization-violating effects when they are present.

   hep-phPRD(2017)·58 citations
3. 03*

   Lepton Portal Limit of Inert Higgs Doublet Dark Matter with Radiative Neutrino Mass

   Debasish Borah🇮🇳 · Soumya Sadhukhan🇮🇳 · Shibananda Sahoo🇮🇳

   We study an extension of the Inert Higgs Doublet Model (IHDM) by three copies of right handed neutrinos and heavy charged leptons such that both the inert Higgs doublet and the heavy fermions are odd under the $Z_2$ symmetry of the model. The neutrino masses are generated at one loop in the scotogenic fashion. Assuming the neutral scalar of the inert Higgs to be the dark matter candidate, we particularly look into the region of parameter space where dark matter relic abundance is primarily governed by the inert Higgs coupling with the leptons. This corresponds to tiny Higgs portal coupling of dark matter as well as large mass splitting within different components of the inert Higgs doublet suppressing the coannihilations. Such lepton portal couplings can still produce the correct relic abundance even if the Higgs portal couplings are arbitrarily small. Such tiny Higgs portal couplings may be responsible for suppressed dark matter nucleon cross section as well as tiny invisible branching ratio of the standard model Higgs, to be probed at ongoing and future experiments. We also briefly discuss the collider implications of such a scenario.

   hep-phPLB(2017)·34 citations
4. 04*

   Reconsideration of the $B\to K^{\ast }$ Transition Form Factors within the QCD Light-Cone Sum Rules

   Wei Cheng🇨🇳 · Xing-Gang Wu🇨🇳 · Hai-Bing Fu🇨🇳

   In this paper, we study the $B\to K^{\ast }$ transition form factors (TFFs) within the QCD light-cone sum rules (LCSR) approach. Two correlators, i.e. the usual one and the right-handed one, are adopted in the LCSR calculation. The resultant LCSRs for the $B\to K^{\ast }$ TFFs are arranged according to the twist structure of the $K^{\ast }$-meson light-cone distribution amplitudes (LCDAs), whose twist-2, twist-3 and twist-4 terms behave quite differently by using different correlators. We observe that the twist-4 LCDAs, though generally small, shall have sizable contributions to the TFFs $A_{1/2}$, $V$ and $T_1$, thus the twist-4 terms should be kept for a sound prediction. We also observe that even though different choices of the correlator lead to different LCSRs with different twist contributions, the large correlation coefficients for most of the TFFs indicate that the LCSRs for different correlators are close to each order, not only for their values at the large recoil point $q^2=0$ but also for their ascending trends in whole $q^2$-region. Such a high degree of correlation is confirmed by their application to the branching fraction of the semi-leptonic decay $B\to K^{\ast }{\mu }^{+}{\mu }^{-}$. Thus, a proper choice of correlator may inversely provide a chance for probing uncertain LCDAs, i.e. the contributions from those LCDAs can be amplified to a certain degree via a proper choice of correlator, thus amplifying the sensitivity of the TFFs, and hence their related observables, to those LCDAs.

   hep-phPRD(2017)·16 citations
5. 05*

   Hidden sector behind the CKM matrix

   Shohei Okawa🇯🇵 · Yuji Omura🇯🇵

   The small quark mixing, described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix in the Standard Model, may be a clue to reveal new physics around the TeV scale. We consider a simple scenario that extra particles in a hidden sector radiatively mediate the flavor violation to the quark sector around the TeV scale and effectively realize the observed CKM matrix. The lightest particle in the hidden sector, whose contribution to the CKM matrix is expected to be dominant, is a good dark matter (DM) candidate, so we focus on the contribution, and discuss the DM physics. In this scenario, there is an explicit relation between the CKM matrix and flavor violating couplings, such as four-quark couplings, because both are radiatively induced by the particles in the hidden sector. Then, we can explicitly find the DM mass region and the size of Yukawa couplings between the DM and quarks, based on the study of flavor physics and DM physics. In conclusion, we show that DM mass in our scenario is around the TeV scale, and the Yukawa couplings are between $\mathcal{O}(0.01)$ and $\mathcal{O}(1)$. The spin-independent DM scattering cross section is estimated as $\mathcal{O}(10^{-9})$ [pb]. An extra colored particle is also predicted at the $\mathcal{O}(10)$ TeV scale.

   hep-phhep-exPRD(2017)·4 citations
6. 06*

   Looking for New Physics via Semi-leptonic and Leptonic rare decays of $D$ and $D_s$

   Xing-Dao Guo🇨🇳 · Xi-Qing Hao🇨🇳 · Hong-Wei Ke · Ming-Gang Zhao🇨🇳 · Xue-Qian Li🇨🇳

   It is well recognized that looking for new physics at lower energy colliders is a tendency which is complementary to high energy machines such as LHC. Based on large database of BESIII, we may have a unique opportunity to do a good job. In this paper we calculate the branching ratios of semi-leptonic processes $D_s^{+}\to K^{+}{e}^{-}{e}^{+}$, $D_s^{+}\to K^{+}{e}^{-}{\mu }^{+}$ and leptonic processes $D^0\to e^{-}{e}^{+}$, $D^0\to e^{-}{\mu }^{+}$ in the frames of $U(1{)}^{\prime }$ model, 2HDM and unparticle separately. It is found that both the $U(1{)}^{\prime }$ and 2HDM may influence the semi-leptonic decay rates, but only the $U(1{)}^{\prime }$ offers substantial contributions to the pure leptonic decays and the resultant branching ratio of $D^0\to e^{-}{\mu }^{+}$ can be as large as $10^{-7}\sim 10^{-8}$ which might be observed at the future super $\tau$-charm factory.

   hep-phCPC(2017)·13 citations
7. 07*

   The structure of pentaquarks ${\Omega }_c^0$ in the chiral quark model

   Gang Yang🇨🇳 · Jialun Ping🇨🇳

   Recently, the experimental results of LHCb Collaboration suggested the existence of five new excited states of ${\Omega }_c^0$, ${\Omega }_c(3000{)}^0$, ${\Omega }_c(3050{)}^0$, ${\Omega }_c(3066{)}^0$, ${\Omega }_c(3090{)}^0$ and ${\Omega }_c(3119{)}^0$, the quantum numbers of these new particles are not determined now. To understand the nature of the states, a dynamical calculation of 5-quark systems with quantum numbers $I{J}^P=0(\frac{1}{2}{)}^{-}$, $0(\frac{3}{2}{)}^{-}$ and $0(\frac{5}{2}{)}^{-}$ is performed in the framework of chiral quark model with the help of gaussian expansion method. The results show the $\Xi -\bar{D}$, ${\Xi }_c\bar{K}$ and ${\Xi }_c^{\ast }\bar{K}$ are possible the candidates of these new particles. The distances between quark pairs suggest that the nature of pentaquark states.

   hep-phhep-exPRD(2018)·73 citations
8. 08*

   Out-of-Equilibrium Chiral Magnetic Effect from Chiral Kinetic Theory

   Anping Huang🇨🇳 · Yin Jiang🇩🇪 · Shuzhe Shi🇺🇸 · Jinfeng Liao🇺🇸 · Pengfei Zhuang🇨🇳

   Recently there has been significant interest in the macroscopic manifestation of chiral anomaly in many-body systems of chiral fermions. A notable example is the Chiral Magnetic Effect (CME). Enthusiastic efforts have been made to search for the CME in the quark-gluon plasma created in heavy ion collisions. A crucial challenge is that the extremely strong magnetic field in such collisions may last only for a brief moment and the CME current may have to occur at so early a stage that the quark-gluon matter is still far from thermal equilibrium. This thus requires modeling of the CME in an out-of-equilibrium setting. With the recently developed theoretical tool of chiral kinetic theory, we make a first phenomenological study of the CME-induced charge separation during the pre-thermal stage in heavy ion collisions. The effect is found to be very sensitive to the time dependence of the magnetic field and also influenced by the initial quark momentum spectrum as well as the relaxation time of the system evolution toward thermal equilibrium. Within the present approach, such pre-thermal charge separation is found to be modest.

   hep-phhep-thPLB(2018)·49 citations
9. 09*

   Uncover Compressed Supersymmetry via Boosted Bosons from the Heavier Stop/Sbottom

   Zhaofeng Kang🇰🇷 · Jinmian Li🇰🇷 · Mengchao Zhang🇰🇷

   A light stop around the weak scale is a hopeful messenger of natural supersymmetry (SUSY), but it has not shown up at the current stage of LHC. Such a situation raises the question of the fate of natural SUSY. Actually, a relatively light stop can easily be hidden in a compressed spectra such as mild mass degeneracy between stop and neutralino plus top quark. Searching for such a stop at the LHC is a challenge. On the other hand, in terms of the argument of natural SUSY, other members in the stop sector, including a heavier stop ${\tilde{t}}_2$ and lighter sbottom ${\tilde{b}}_1$ (both assumed to be left-handed-like), are also supposed to be relatively light and therefore searching for them would provide an alternative method to probe natural SUSY with a compressed spectrum. In this paper we consider quasi-natural SUSY which tolerates relatively heavy colored partners near the TeV scale, with a moderately large mass gap between the heavier members and the lightest stop. Then $W/Z/h$ as companions of ${\tilde{t}}_2$ and ${\tilde{b}}_1$ decaying into ${\tilde{t}}_1$ generically are well boosted, and they, along with other visible particles from ${\tilde{t}}_1$ decay, are a good probe to study compressed SUSY. We find that the resulting search strategy with boosted bosons can have better sensitivity than those utilizing multi-leptons.

   hep-phhep-exEPJC(2017)·7 citations
10. 10*

    Halo-independent determination of the unmodulated WIMP signal in DAMA: the isotropic case

    Paolo Gondolo (Utah U.)🇺🇸 · Stefano Scopel (Sogang U.)🇰🇷

    We present a halo-independent determination of the unmodulated signal corresponding to the DAMA modulation if interpreted as due to dark matter weakly interacting massive particles (WIMPs). First we show how a modulated signal gives information on the WIMP velocity distribution function in the Galactic rest frame, from which the unmodulated signal descends. Then we perform a mathematically-sound profile likelihood analysis in which we profile the likelihood over a continuum of nuisance parameters (namely, the WIMP velocity distribution). As a first application of the method, which is very general and valid for any class of velocity distributions, we restrict the analysis to velocity distributions that are isotropic in the Galactic frame. In this way we obtain halo-independent maximum-likelihood estimates and confidence intervals for the DAMA unmodulated signal. We find that the estimated unmodulated signal is in line with expectations for a WIMP-induced modulation and is compatible with the DAMA background+signal rate. Specifically, for the isotropic case we find that the modulated amplitude ranges between a few percent and about 25% of the unmodulated amplitude, depending on the WIMP mass.

    hep-phastro-ph.COJCAP(2017)·28 citations
11. 11*

    Variational path-integral approach to back-reactions of composite mesons in the Nambu-Jona-Lasinio model

    D. Blaschke🇷🇺 · D. Ebert🇩🇪

    For the investigation of back-reactions of composite mesons in the NJL model, a variational path-integral treatment is formulated which yields an effective action ${\mathcal{A}}_{\mathrm{eff}}[D_{\sigma },D_{\pi };S]$, depending on the propagators $D_{\sigma }$, $D_{\pi }$ of $\sigma -$ and $\pi -$mesons and on the full quark propagator $S$. The stationarity conditions $\delta {\mathcal{A}}_{\mathrm{eff}}/\delta S=0$, $\delta {\mathcal{A}}_{\mathrm{eff}}/\delta D_{\sigma }=0$, $\delta {\mathcal{A}}_{\mathrm{eff}}/\delta D_{\pi }=0$, then lead to coupled Schwinger-Dyson (SD) equations for the quark self-energy and the meson polarization functions. These results reproduce and extend results of the so-called "$\Phi -$derivable" approach and provide a functional formulation for diagrammatic resummations of $1/N_c-$corrections in the NJL model. Finally, we perform a low-momentum estimate of the quark and meson loop contributions to the polarization function of the pion and on this basis discuss the Goldstone theorem.

    hep-phnucl-thNPB(2017)·8 citations
12. 12*

    Hillclimbing inflation

    Ryusuke Jinno🇰🇷 · Kunio Kaneta🇰🇷

    We propose a new class of inflationary models in which inflation takes place while the inflaton is climbing up a potential hill due to a coupling to gravity. We study their attractor behavior, and investigate its relation with known attractors. We also discuss a possible realization of this type of models with the natural inflation, and show that the inflationary predictions come well within the region consistent with the observation of the cosmic microwave background.

    hep-phgr-qchep-thPRD(2017)·28 citations
13. 13*

    Corona effect in AA collisions at LHC

    V.S. Pantuev🇷🇺

    Following our earlier finding based on RHIC data on the dominant jet production from nucleus corona region, we reconsider this effect in nucleus-nucleus collisions at LHC energy. Our hypothesis was based on experimental data, which raised the idea of a finite formation time for the produced medium. At RHIC energy and in low density corona region this time reaches about 2 fm/c. All observed high p_t particles are produced in the corona region and have a chance to escape during this 2 fm/c. After that, the formed high density matter absorbs all jets. Following this hypothesis, the nuclear modification factor R_{AA} should be independent on particle momentum and be flat versus p_t. At the same time, we describe the finite azimuthal anisotropy of high p_t particles, v_2. A separate prediction held that, at LHC energy, the formation time in the corona region should be two times smaller, about 1 fm/c. New data at LHC show that R_{AA} is not flat and is rising with p_t. We add to our original hypothesis an assumption that a fast parton traversing the produced medium loses the fixed portion of its energy. A shift of about 7 GeV (I would call it as a parton binding energy) from the original power law p^{-6} production cross section in pp explains well all the observed R_{AA} dependencies. The shift of about 7 GeV is also valid at RHIC energy, where the cross section follows a power law with about p^{-8} and this shift explains a very slow rise of R_{AA} seen for neutral pions with p_t above 15 GeV/c. We also show that the observed at LHC dependence of v_2 at high p_t and our previous predictions agree.

    hep-phnucl-exnucl-thJETP Lett.(2017)·0 citations
14. 14*

    Zero Points of Chiral Condensate

    V.G. Ksenzov🇷🇺 · A.I. Romanov🇷🇺

    We investigate a model with a massless fermion and a massive scalar field with the Yukawa interaction between these two fields. The model possess a discrete symmetry. The chiral condensate is calculated in one-loop approximation in $(1+1)$-dimensional spacetime. It was shown that the chiral condensate vanishes at two different values of the coupling constant. At the first of them there is a phase transition in which the discrete symmetry is restored. At the second zero of the chiral condensate it takes place a phase transition which distinguishes the positive ${\mu }^2$ from the negative ${\mu }^2$, where ${\mu }^2$ is an effective mass of the scalar field.

    hep-ph1 citation
15. 15*

    Generating a resonance-like structure in the reaction $B_c\to B_s\pi \pi$

    Xiao-Hai Liu🇩🇪 · Ulf-G. Meißner🇩🇪

    We investigate the process $B_c^{+}\to B_s^0{\pi }^{+}{\pi }^0$ via $B{\bar{K}}^{\ast }$ rescattering. The kinematic conditions for triangle singularities are perfectly satisfied in the rescattering diagrams. A resonance-like structure around the $B\bar{K}$ threshold, which we denote as $X(5777)$, is predicted to be present in the invariant mass distribution of $B_s^0{\pi }^{+}$. Because the relative weak $B\bar{K}$ $(I=1)$ interaction does not support the existence of a dynamically generated hadronic molecule, the $X(5777)$ can be identified as a pure kinematical effect due to the triangle singularity. Its observation may help to establish a non-resonance interpretation for some $XYZ$ particles.

    hep-phhep-exnucl-thEPJC(2017)·25 citations
16. 16*

    $W^{\pm }Z$ production at the LHC: fiducial cross sections and distributions in NNLO QCD

    Massimiliano Grazzini🇨🇭 · Stefan Kallweit🇨🇭 · Dirk Rathlev🇨🇭 · Marius Wiesemann🇨🇭

    We report on the first fully differential calculation for $W^{\pm }Z$ production in hadron collisions up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. Leptonic decays of the $W$ and $Z$ bosons are consistently taken into account, i.e. we include all resonant and non-resonant diagrams that contribute to the process $pp\to {\ell }^{{}^{\prime }\pm }{\nu }_{{\ell }^{{}^{\prime }}}{\ell }^{+}{\ell }^{-}+X$ both in the same-flavour (${\ell }^{\prime }=\ell$) and the different-flavour (${\ell }^{\prime }\ne \ell$) channel. Fiducial cross sections and distributions are presented in the presence of standard selection cuts applied in the experimental $W^{\pm }Z$ analyses by ATLAS and CMS at centre-of-mass energies of 8 and 13\,TeV. As previously shown for the inclusive cross section, NNLO corrections increase the NLO result by about $10\%$, thereby leading to an improved agreement with experimental data. The importance of NNLO accurate predictions is also shown in the case of new-physics scenarios, where, especially in high-$p_T$ categories, their impact can reach $\mathcal{O}(20\%)$. The availability of differential NNLO predictions will play a crucial role in the rich physics programme that is based on precision studies of $W^{\pm }Z$ signatures at the LHC.

    hep-phhep-exJHEP(2017)·130 citations
17. 17*

    Comments on "Study of $J/\psi$ production in jets"

    I. Belyaev🇷🇺 · A. V. Berezhnoy🇷🇺 · A. K. Likhoded🇷🇺 · A. V. Luchinsky🇷🇺

    Recent LHCb measurements of the $J/\psi$ meson production in jets is analyzed using fragmentation jet function formalism. It is shown that disagreement with theoretical predictions for distribution over the fraction of $J/\psi$ transverse momentum $z(J/\psi )$ in the cases of prompt production can be explained if one takes into account evolution of the fragmentation function and contributions from double parton scattering mechanism.

    hep-phhep-exMod.Phys.Lett.A(2017)·5 citations
18. 18*

    Discovery Potentials of Doubly Charmed Baryons

    Fu-Sheng Yu🇨🇳 · Hua-Yu Jiang🇨🇳 · Run-Hui Li🇨🇳 · Cai-Dian Lü🇨🇳 · Wei Wang🇨🇳 · Zhen-Xing Zhao🇨🇳

    The existence of doubly heavy flavor baryons has not been well established experimentally so far. In this Letter we systematically investigate the weak decays of the doubly charmed baryons, ${\Xi }_{cc}^{++}$ and ${\Xi }_{cc}^{+}$, which would be helpful for experimental searches for these particles. The branching fractions are studied under the factorization hypothesis for the short-distance contributions and considering the rescattering effect for the long-distance contributions which are significantly enhanced. Comparing all the decay modes, we recommend the processes of ${\Xi }_{cc}^{++}\to {\Lambda }_c^{+}{K}^{-}{\pi }^{+}{\pi }^{+}$ and ${\Xi }_c^{+}{\pi }^{+}$ as the first priority for experiments to search for the doubly heavy baryons.

    hep-phCPC(2018)·179 citations
19. 19*

    Understanding the newly observed ${\Omega }_c$ states through their decays

    Kai-Lei Wang🇨🇳 · Li-Ye Xiao🇨🇳 · Xian-Hui Zhong🇨🇳 · Qiang Zhao🇨🇳

    The strong and radiative decay properties of the low-lying ${\Omega }_c$ states are studied in a constituent quark model. We find that the newly observed ${\Omega }_c$ states by the LHCb Collaboration can fit in well the decay patterns. Thus, their spin-parity can be possibly assigned as the following: (i) The ${\Omega }_c(3000)$ has $J^P=1/2^{-}$ and corresponds to the narrow $1P$ mixed state $|1^2{P}_{\lambda }{\frac{1}{2}}^{-}{⟩}_1$, its partner $|1^2{P}_{\lambda }{\frac{1}{2}}^{-}{⟩}_2$ should be a broad state with a width of $\sim 100$ MeV. (ii) The ${\Omega }_c(3050)$ and ${\Omega }_c(3066)$ can be assigned to be two $J^P=3/2^{-}$ states, $|1^4{P}_{\lambda }{\frac{3}{2}}^{-}⟩$ and $|1^2{P}_{\lambda }{\frac{3}{2}}^{-}⟩$, respectively. (iii) The ${\Omega }_c(3090)$ can be assigned as the $|1^4{P}_{\lambda }{\frac{5}{2}}^{-}⟩$ state with $J^P=5/2^{-}$. (iv) The ${\Omega }_c(3119)$ might correspond to one of the two $2S$ states of the first radial excitations, i.e. $|2^2{S}_{\lambda \lambda }{\frac{1}{2}}^{+}⟩$ or $|2^4{S}_{\lambda \lambda }{\frac{3}{2}}^{+}⟩$.

    hep-phPRD(2017)·111 citations
20. 20*

    Dark Matter, Muon $g-2$, Electric Dipole Moments and $Z\to {\ell }_i^{+}{\ell }_j^{-}$ in a One-Loop Induced Neutrino Model

    Cheng-Wei Chiang🇹🇼 · Hiroshi Okada🇹🇼 · Eibun Senaha🇹🇼

    We study a simple one-loop induced neutrino mass model that contains both bosonic and fermionic dark matter candidates and has the capacity to explain the muon anomalous magnetic moment anomaly. We perform a comprehensive analysis by taking into account the relevant constraints of charged lepton flavor violation, electric dipole moments, and neutrino oscillation data. We examine the constraints from lepton flavor-changing $Z$ boson decays at one-loop level, particularly when the involved couplings contribute to the muon $g-2$. It is found that $\text{BR}(Z\to \mu \tau )\simeq (10^{-7}$ - $10^{-6})$ while $\text{BR}(\tau \to \mu \gamma )\lesssim 10^{-11}$ in the fermionic dark matter scenario. The former can be probed by the precision measurement of the $Z$ boson at future lepton colliders.

    hep-phPRD(2017)·36 citations
21. 21*

    Optimized velocity distributions for direct dark matter detection

    Alejandro Ibarra🇩🇪 · Andreas Rappelt🇩🇪

    We present a method to calculate, without making assumptions about the local dark matter velocity distribution, the maximal and minimal number of signal events in a direct detection experiment given a set of constraints from other direct detection experiments and/or neutrino telescopes. The method also allows to determine the velocity distribution that optimizes the signal rates. We illustrate our method with three concrete applications: i) to derive a halo-independent upper limit on the cross section from a set of null results, ii) to confront in a halo-independent way a detection claim to a set of null results and iii) to assess, in a halo-independent manner, the prospects for detection in a future experiment given a set of current null results.

    hep-phastro-ph.COJCAP(2017)·31 citations
22. 22*

    Charmed mesons with a symmetry-preserving contact interaction

    Fernando E. Serna🇧🇷 · Bruno El-Bennich🇧🇷 · Gastão Krein🇧🇷

    A symmetry-preserving treatment of a vector-vector contact interaction is used to study charmed heavy-light mesons. The contact interaction is a representation of nonperturbative kernels used in Dyson-Schwinger and Bethe-Salpeter equations of QCD. The Dyson-Schwinger equation is solved for the $u,d,s$ and $c$ quark propagators and the bound-state Bethe-Salpeter amplitudes respecting spacetime-translation invariance and the Ward-Green-Takahashi identities associated with global symmetries of QCD are obtained to calculate masses and electroweak decay constants of the pseudoscalar $\pi ,K$, $D$ and $D_s$ and vector $\rho$, $K^{\ast }$, $D^{\ast }$, and $D_s^{\ast }$ mesons. The predictions of the model are in good agreement with available experimental and lattice QCD data.

    hep-phhep-latnucl-thPRD(2017)·57 citations
23. 23*

    Status of the $B\to K^{\ast }{\mu }^{+}{\mu }^{-}$ anomaly after Moriond 2017

    Wolfgang Altmannshofer🇺🇸 · Christoph Niehoff🇩🇪 · Peter Stangl🇩🇪 · David M. Straub🇩🇪

    Motivated by recent results by the ATLAS and CMS collaborations on the angular distribution of the $B\to K^{\ast }{\mu }^{+}{\mu }^{-}$ decay, we perform a state-of-the-art analysis of rare $B$ meson decays based on the $b\to s\mu \mu$ transition. Using standard estimates of hadronic uncertainties, we confirm the presence of a sizable discrepancy between data and SM predictions. We do not find evidence for a $q^2$ or helicity dependence of the discrepancy. The data can be consistently described by new physics in the form of a four-fermion contact interaction $(\bar{s}{\gamma }_{\alpha }{P}_{L}b)(\bar{\mu }{\gamma }^{\alpha }\mu )$. Assuming that the new physics affects decays with muons but not with electrons, we make predictions for a variety of theoretically clean observables sensitive to violation of lepton flavour universality.

    hep-phhep-exEPJC(2017)·183 citations
24. 24*

    Nucleon spin structure functions at NNLO in the presence of target mass corrections and higher twist effects

    Hamzeh Khanpour🇮🇷 · Sara Taheri Monfared🇮🇷 · S. Atashbar Tehrani🇮🇷

    We extract polarized parton distribution functions (PPDFs), referred to as "KTA17," together with the highly correlated strong coupling ${\alpha }_s$ from recent and up-to-date $g_1$ and $g_2$ polarized structure functions world data at next-to-next-to-leading order in perturbative QCD. The stability and reliability of the results are ensured by including nonperturbative target mass corrections as well as higher-twist terms which are particularly important at the large-$x$ region at low Q${}^2$. Their role in extracting the PPDFs in the nucleon is studied. Sum rules are discussed and compared with other results from the literature. This analysis is made by means of the Jacobi polynomials expansion technique to the DGLAP evolution. The uncertainties on the observables and on the PPDFs throughout this paper are computed using standard Hessian error propagation which served to provide a more realistic estimate of the PPDFs uncertainties.

    hep-phPRD(2017)·42 citations
25. 25*

    Simultaneous Explanation of $R(D^{(\ast )})$ and $b\to s{\mu }^{+}{\mu }^{-}$: The Last Scalar Leptoquarks Standing

    Andreas Crivellin🇨🇭 · Dario Müller🇨🇭 · Toshihiko Ota🇪🇨

    Over the past years, experiments accumulated intriguing hints for new physics (NP) in flavor observables, namely in the anomalous magnetic moment of the muon ($a_{\mu }$), in $R(D^{(\ast )})=\mathrm{Br}(B\to D^{(\ast )}\tau \nu )/\mathrm{Br}(B\to D^{(\ast )}\ell \nu )$ and in $b\to s{\mu }^{+}{\mu }^{-}$ transitions, which are all at the $3-4\sigma$ level. In this article we point out that one can explain the $R(D^{(\ast )})$ anomaly using two scalar leptoquarks (LQs) with the same mass and coupling to fermions related via a discrete symmetry: an $SU(2)$ singlet and an $SU(2)$ triplet, both with hypercharge $Y=-2/3$. In this way, potentially dangerous contributions to $b\to s\nu \nu$ are avoided and non-CKM suppressed effects in $R(D^{(\ast )})$ can be generated. This allows for smaller overall couplings to fermions weakening the direct LHC bounds. In our model, $R(D^{(\ast )})$ is directly correlated to $b\to s{\tau }^{+}{\tau }^{-}$ transitions where an enhancement by orders of magnitude compared to the standard model (SM) is predicted, such that these decay modes are in the reach of LHCb and BELLE II. Furthermore, one can also naturally explain the $b\to s{\mu }^{+}{\mu }^{-}$ anomalies (including $R(K)$) by a $C_9=-C_{10}$ like contribution without spoiling $\mu -e$ universality in charged current decays. In this case sizable effects in $b\to s\tau \mu$ transitions are predicted which are again well within the experimental reach. One can even address the longstanding anomaly in $a_{\mu }$, generating a sizable decay rate for $\tau \to \mu \gamma$. However, we find that out of the three anomalies $R(D^{(\ast )})$, $b\to s{\mu }^{+}{\mu }^{-}$ and $a_{\mu }$ only two (but any two) can be explained simultaneously.

    hep-phhep-exJHEP(2017)·404 citations
26. 26*

    Generic calculation of two-body partial decay widths at the full one-loop level

    Mark D. Goodsell🇫🇷 · Stefan Liebler🇩🇪 · Florian Staub🇩🇪

    We describe a fully generic implementation of two-body partial decay widths at the full one-loop level in the SARAH and SPheno framework compatible with most supported models. It incorporates fermionic decays to a fermion and a scalar or a gauge boson as well as scalar decays into two fermions, two gauge bosons, two scalars or a scalar and a gauge boson. We present the relevant generic expressions for virtual and real corrections. Whereas wavefunction corrections are determined from on-shell conditions, the parameters of the underlying model are by default renormalised in a DR (or MS) scheme. However, the user can also define model-specific counter-terms. As an example we discuss the renormalisation of the electric charge in the Thomson limit for top-quark decays in the standard model. One-loop induced decays are also supported. The framework additionally allows the addition of mass and mixing corrections induced at higher orders for the involved external states. We explain our procedure to cancel infra-red divergences for such cases, which is achieved through an infra-red counter-term taking into account corrected Goldstone boson vertices. We compare our results for sfermion, gluino and Higgs decays in the minimal supersymmetric standard model (MSSM) against the public codes SFOLD, FVSFOLD and HFOLD and explain observed differences. Radiative induced gluino and neutralino decays are compared against the original implementation in SPheno in the MSSM. We exactly reproduce the results of the code CNNDecays for decays of neutralinos and charginos in R-parity violating models. The new version SARAH 4.11.0 by default includes the calculation of two-body decay widths at the full one-loop level. Current limitations for certain model classes are described.

    hep-phEPJC(2017)·80 citations
27. 27*

    The study of the extended Higgs boson sector within 2HDM model

    T.V. Obikhod🇺🇦 · E.A. Petrenko🇺🇦

    Consideration of the latest experimental data on the searches for extended sector of Higgs bosons produced at the LHC at a center-of-mass energy of 13 TeV, allows for computer modeling of the properties of supersymmetric particles within 2HDM model. The experimental restrictions on model parameters accounted in FeynHiggs code that is implemented in SusHi program, gave us the possibility to calculate the cross sections and branching fractions for three mechanisms of production and decay of Higgs bosons: 1) pp$\to H\to \tau \tau$, 2) pp$\to A\to Zh\to llbb$, 3) pp$\to H\to hh\to bb\tau \tau$ at a center-of-mass energy of 14 TeV. The considered computer modelling make it possible to draw conclusions about the need to take into account the b-associated production process of Higgs bosons for fermionic decay channel at large values of tan$\beta$. Differential cross sections with respect to the Higgs transverse momentum $p_t$ and pseudorapidity $\eta$ are calculated and the peculiarities of the kinematics of the Higgs boson decay products are recognized.

    hep-phProb.Atomic Sci.Technol.(2017)·2 citations
28. 28*

    Higher-Order Scheme-Independent Series Expansions of ${\gamma }_{\bar{\psi }\psi ,IR}$ and ${\beta }_{IR}^{\prime }$ in Conformal Field Theories

    Thomas A. Ryttov🇩🇰 · Robert Shrock🇺🇸

    We study a vectorial asymptotically free gauge theory, with gauge group $G$ and $N_f$ massless fermions in a representation $R$ of this group, that exhibits an infrared (IR) zero in its beta function, $\beta$, at the coupling $\alpha ={\alpha }_{IR}$ in the non-Abelian Coulomb phase. For general $G$ and $R$, we calculate the scheme-independent series expansions of (i) the anomalous dimension of the fermion bilinear, ${\gamma }_{\bar{\psi }\psi ,IR}$, to $O({\Delta }_f^4)$ and (ii) the derivative ${\beta }^{\prime }=d\beta /d\alpha$, to $O({\Delta }_f^5)$, both evaluated at ${\alpha }_{IR}$, where ${\Delta }_f$ is an $N_f$-dependent expansion variable. These are the highest orders to which these expansions have been calculated. We apply these general results to theories with $G=\mathrm{SU}(N_c)$ and $R$ equal to the fundamental, adjoint, and symmetric and antisymmetric rank-2 tensor representations. It is shown that for all of these representations, ${\gamma }_{\bar{\psi }\psi ,IR}$, calculated to the order ${\Delta }_f^p$, with $1\le p\le 4$, increases monotonically with decreasing $N_f$ and, for fixed $N_f$, is a monotonically increasing function of $p$. Comparisons of our scheme-independent calculations of ${\gamma }_{\bar{\psi }\psi ,IR}$ and ${\beta }_{IR}^{\prime }$ are made with our earlier higher $n$-loop values of these quantities, and with lattice measurements. For $R=F$, we present results for the limit $N_c\to \infty$ and $N_f\to \infty$ with $N_f/N_c$ fixed. We also present expansions for ${\alpha }_{IR}$ calculated to $O({\Delta }_f^4)$.

    ↳ hep-thhep-lathep-phPRD(2017)·61 citations
29. 29*

    Detection prospects for the Cosmic Neutrino Background using laser interferometers

    Valerie Domcke🇫🇷 · Martin Spinrath🇹🇼

    The cosmic neutrino background is a key prediction of Big Bang cosmology which has not been observed yet. The movement of the earth through this neutrino bath creates a force on a pendulum, as if it was exposed to a cosmic wind. We revise here estimates for the resulting pendulum acceleration and compare it to the theoretical sensitivity of an experimental setup where the pendulum position is measured using current laser interferometer technology as employed in gravitational wave detectors. We discuss how a significant improvement of this setup can be envisaged in a micro gravity environment. The proposed setup could simultaneously function as a dark matter detector in the sub-MeV range, which currently eludes direct detection constraints.

    ↳ astro-ph.COhep-exhep-phJCAP(2017)·63 citations
30. 30*

    Matching issue in quasi parton distribution approach

    Tomomi Ishikawa🇨🇳 · Yan-Qing Ma🇨🇳 · Jian-Wei Qiu🇺🇸 · Shinsuke Yoshida🇺🇸

    In recent years, the quasi parton distribution has been introduced for extracting the parton distribution functions from lattice QCD simulations. The quasi and standard distribution share the same perturbative collinear singularity and the renormalized quasi distribution can be factorized into the standard distribution with a perturbative matching factor. The quasi parton distribution is known to have power-law UV divergences, which do not exist in the standard distribution. We discuss in this talk the nonperturbative renormalization scheme for the power divergence. We also demonstrate the perturbative matching of the quasi quark distribution between continuum and lattice at the one-loop.

    ↳ hep-lathep-phnucl-thPoS(2016)·4 citations
31. 31*

    Relativistic magnetohydrodynamics

    Juan Hernandez🇨🇦 · Pavel Kovtun🇨🇦

    We present the equations of relativistic hydrodynamics coupled to dynamical electromagnetic fields, including the effects of polarization, electric fields, and the derivative expansion. We enumerate the transport coefficients at leading order in derivatives, including electrical conductivities, viscosities, and thermodynamic coefficients. We find the constraints on transport coefficients due to the positivity of entropy production, and derive the corresponding Kubo formulas. For the neutral state in a magnetic field, small fluctuations include Alfven waves, magnetosonic waves, and the dissipative modes. For the state with a non-zero dynamical charge density in a magnetic field, plasma oscillations gap out all propagating modes, except for Alfven-like waves with a quadratic dispersion relation. We relate the transport coefficients in the "conventional" magnetohydrodynamics (formulated using Maxwell's equations in matter) to those in the "dual" version of magnetohydrodynamics (formulated using the conserved magnetic flux).

    ↳ hep-thhep-phnucl-thJHEP(2017)·172 citations
32. 32*

    Nucleon scalar and tensor charges using lattice QCD simulations at the physical value of the pion mass

    C. Alexandrou (1, 2)🇨🇾 · M. Constantinou (3)🇺🇸 · P. Dimopoulos (4)🇮🇹 · R. Frezzotti (Rome Tor Vergata)🇮🇹 · K. Hadjiyiannakou (2)🇨🇾 · K. Jansen (5)🇩🇪 · C. Kallidonis (2)🇨🇾 · B. Kostrzewa (6)🇩🇪 · G. Koutsou (2)🇨🇾 · M. Mangin-Brinet (7)🇫🇷 · A. Vaquero Avilès-Casco (8)🇺🇸 · U. Wenger (9) ((1) Univ. of Cyprus, (2) The Cyprus Inst., (3) Temple Univ., (4) Centro Fermi & Rome Tor Vergata, (5) DESY-Zeuthen, (6) Bonn Univ., (7) Grenoble, (8) Univ. of Utah, (9) Univ. of Bern)🇨🇭

    We present results on the light, strange and charm nucleon scalar and tensor charges from lattice QCD, using simulations with $N_f=2$ flavors of twisted mass Clover-improved fermions with a physical value of the pion mass. Both connected and disconnected contributions are included, enabling us to extract the isoscalar, strange and charm charges for the first time directly at the physical point. Furthermore, the renormalization is computed non-perturbatively for both isovector and isoscalar quantities. We investigate excited state effects by analyzing several sink-source time separations and by employing a set of methods to probe ground state dominance. Our final results for the scalar charges are $g_S^u=5.20(42)(15)(12)$, $g_S^d=4.27(26)(15)(12)$, $g_S^s=0.33(7)(1)(4)$, $g_S^c=0.062(13)(3)(5)$ and for the tensor charges $g_T^u=0.782(16)(2)(13)$, $g_T^d=-0.219(10)(2)(13)$, $g_T^s=-0.00319(69)(2)(22)$, $g_T^c=-0.00263(269)(2)(37)$ in the $\overline{\mathrm{MS}}$ scheme at 2~GeV. The first error is statistical, the second is the systematic error due to the renormalization and the third the systematic arising from possible contamination due to the excited states.

    ↳ hep-lathep-phnucl-exnucl-thPRD(2017)·78 citations
33. 33*

    Light axion-like dark matter must be present during inflation

    Luca Visinelli🇸🇪

    Axion-like particles (ALPs) might constitute the totality of the cold dark matter (CDM) observed. The parameter space of ALPs depends on the mass of the particle $m$ and on the energy scale of inflation $H_I$ , the latter being bound by the non-detection of primordial gravitational waves. We show that the bound on HI implies the existence of a mass scale $m_{\chi }=10\mathrm{neV}÷0.5\mathrm{peV}$, depending on the ALP susceptibility $\chi$, such that the energy density of ALPs of mass smaller than $m_{\chi }$ is too low to explain the present CDM budget, if the ALP field has originated after the end of inflation. This bound affects Ultra-Light Axions (ULAs), which have recently regained popularity as CDM candidates. Light ($m<m_{\chi }$) ALPs can then be CDM candidates only if the ALP field has already originated during the inflationary period, in which case the parameter space is constrained by the non-detection of axion isocurvature fluctuations. We comment on the effects on these bounds from additional physics beyond the Standard Model, besides ALPs.

    ↳ astro-ph.COhep-phPRD(2017)·74 citations
34. 34*

    Gross-Neveu-Yukawa model at three loops and Ising critical behavior of Dirac systems

    Luminita N. Mihaila🇩🇪 · Nikolai Zerf🇩🇪 · Bernhard Ihrig🇩🇪 · Igor F. Herbut🇨🇦 · Michael M. Scherer🇩🇪

    Dirac and Weyl fermions appear as quasi-particle excitations in many different condensed-matter systems. They display various quantum transitions which represent unconventional universality classes related to the variants of the Gross-Neveu model. In this work we study the bosonized version of the standard Gross-Neveu model -- the Gross-Neveu-Yukawa theory -- at three-loop order, and compute critical exponents in $4-ϵ$ dimensions for general number of fermion flavors. Our results fully encompass the previously known two-loop calculations, and agree with the known three-loop results in the purely bosonic limit of the theory. We also find the exponents to satisfy the emergent super-scaling relations in the limit of a single-component fermion, order by order up to three loops. Finally, we apply the computed series for the exponents and their Padé approximants to several phase transitions of current interest: metal-insulator transitions of spin-1/2 and spinless fermions on the honeycomb lattice, emergent supersymmetric surface field theory in topological phases, as well as the disorder-induced quantum transition in Weyl semimetals. Comparison with the results of other analytical and numerical methods is discussed.

    ↳ cond-mat.str-elhep-phhep-thPRB(2017)·93 citations
35. 35*

    Nuclear physics insights for new-physics searches using nuclei: Neutrinoless $\beta \beta$ decay and dark matter direct detection

    Javier Menéndez🇯🇵

    Experiments using nuclei to probe new physics beyond the Standard Model, such as neutrinoless $\beta \beta$ decay searches testing whether neutrinos are their own antiparticle, and direct detection experiments aiming to identify the nature of dark matter, require accurate nuclear physics input for optimizing their discovery potential and for a correct interpretation of their results. This demands a detailed knowledge of the nuclear structure relevant for these processes. For instance, neutrinoless $\beta \beta$ decay nuclear matrix elements are very sensitive to the nuclear correlations in the initial and final nuclei, and the spin-dependent nuclear structure factors of dark matter scattering depend on the subtle distribution of the nuclear spin among all nucleons. In addition, nucleons are composite and strongly interacting, which implies that many-nucleon processes are necessary for a correct description of nuclei and their interactions. It is thus crucial that theoretical studies and experimental analyses consider $\beta$ decays and dark matter interactions with a coupling to two nucleons, called two-nucleon currents.

    ↳ nucl-thastro-ph.COhep-exhep-ph+1EPJ Web Conf.(2017)·4 citations
36. 36*

    Asymptotic safety of higher derivative quantum gravity non-minimally coupled with a matter system

    Yuta Hamada🇯🇵 · Masatoshi Yamada🇩🇪

    We study asymptotic safety of models of the higher derivative quantum gravity with and without matter. The beta functions are derived by utilizing the functional renormalization group, and non-trivial fixed points are found. It turns out that all couplings in gravity sector, namely the cosmological constant, the Newton constant, and the $R^2$ and $R_{\mu \nu }^2$ coupling constants, are relevant in case of higher derivative pure gravity. For the Higgs-Yukawa model non-minimal coupled with higher derivative gravity, we find a stable fixed point at which the scalar-quartic and the Yukawa coupling constants become relevant. The relevant Yukawa coupling is crucial to realize the finite value of the Yukawa coupling constants in the standard model.

    ↳ hep-thgr-qchep-phJHEP(2017)·126 citations
37. 37*

    Cumulants of event-by-event net-strangeness distributions in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$=7.7-200 GeV from UrQMD model

    Chang Zhou🇨🇳 · Ji Xu🇨🇳 · Xiaofeng Luo🇨🇳 · Feng Liu🇨🇳

    Fluctuations of conserved quantities, such as baryon, electric charge and strangeness number, are sensitive observables in heavy-ion collisions to search for the QCD phase transition and critical point. In this paper, we performed a systematical analysis on the various cumulants and cumulant ratios of event-by-event net-strangeness distributions in Au+Au collisions at $\sqrt{s_{NN}}$=7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV from UrQMD model. We performed a systematical study on the contributions from various strange baryons and mesons to the net-strangeness fluctuations. The results demonstrate that the cumulants and cumulant ratios of net-strangeness distributions extracted from different strange particles show very different centrality and energy dependence behavior. By comparing with the net-kaon fluctuations, we found that the strange baryons play an important role in the fluctuations of net-strangeness. This study can provide useful baselines to study the QCD phase transition and search for the QCD critical point by using the fluctuations of net-strangeness in heavy-ion collisions experiment. It can help us to understand non-critical physics contributions to the fluctuations of net-strangeness.

    ↳ nucl-exhep-exhep-phnucl-thPRC(2017)·28 citations
38. 38*

    Black Holes in Loop Quantum Gravity

    Alejandro Perez🇫🇷

    This is a review of the results on black hole physics in the framework of loop quantum gravity. The key feature underlying the results is the discreteness of geometric quantities at the Planck scale predicted by this approach to quantum gravity. Quantum discreteness follows directly from the canonical quantization prescription when applied to the action of general relativity that is suitable for the coupling of gravity with gauge fields and specially with fermions. Planckian discreteness and causal considerations provide the basic structure for the understanding of the thermal properties of black holes close to equilibrium. Discreteness also provides a fresh new look at more (at the moment) speculative issues such as those concerning the fate of information in black hole evaporation. The hypothesis of discreteness leads also to interesting phenomenology with possible observational consequences. The theory of loop quantum gravity is a developing program. This review reports its achievements and open questions in a pedagogical manner with an emphasis on quantum aspects of black hole physics.

    ↳ gr-qchep-phhep-thRept.Prog.Phys.(2017)·196 citations
39. 39*

    Approaching Confinement Structure for Light Quarks in a Holographic Soft Wall QCD Model

    Meng-Wei Li🇹🇼 · Yi Yang🇹🇼 · Pei-Hung Yuan🇹🇼

    We study confinement-deconfinement phase transition in a holographic soft-wall QCD model. By solving the Einstein-Maxwell-scalar system analytically, we obtain the phase structure of the black hole backgrounds. We then impose probe open strings in such background to investigate the confinement-deconfinement phase transition from different open string configurations under various temperatures and chemical potentials. Furthermore, we study the Wilson loop by calculating the minimal surface of the probing open string world-sheet and obtain the Cornell potential in confinement phase analytically.

    ↳ hep-thhep-phPRD(2017)·56 citations
40. 40*

    Dynamically assisted Sauter-Schwinger effect - non-perturbative versus perturbative aspects

    Greger Torgrimsson🇩🇪 · Christian Schneider🇩🇪 · Johannes Oertel🇩🇪 · Ralf Schützhold🇩🇪

    The Sauter-Schwinger effect predicts the creation of electron-positron pairs out of the quantum vacuum by a strong and slowly varying electric field. This effect can be dynamically assisted by an additional weaker time-dependent field, which may drastically enhance the pair-creation probability. In previous studies, it has been found that the enhancement may crucially depend on the temporal shape of this weaker pulse, e.g., a Gaussian profile $\exp \{-(\omega t{)}^2\}$ or a Sauter pulse $1/{\cosh }^2(\omega t)$ behave quite differently. In order to understand this difference, we make a perturbative expansion in terms of the weaker field while treating the strong electric field non-perturbatively. For a large class of profiles including the Sauter pulse, already the sum of the zeroth-order and the first-order amplitudes of this perturbative expansion yields good agreement. For other cases, such as a Gaussian or sinusoidal profile, this is not true in general and higher orders can yield the dominant contribution - where the dominant order depends on the chosen parameters. Our findings are confirmed by numerical simulations and help us to sort previous results into a bigger picture.

    ↳ hep-thhep-phJHEP(2017)·68 citations
41. 41*

    Calculable mass hierarchies and a light dilaton from gravity duals

    Daniel Elander🇪🇸 · Maurizio Piai🇬🇧

    In the context of gauge/gravity dualities, we calculate the scalar and tensor mass spectrum of the boundary theory defined by a special 8-scalar sigma-model in five dimensions, the background solutions of which include the 1-parameter family dual to the baryonic branch of the Klebanov-Strassler field theory. This provides an example of a strongly-coupled, multi-scale system that yields a parametrically light mass for one of the composite scalar particles: the dilaton. We briefly discuss the implications of these findings towards identifying a satisfactory solution to both the big and little hierarchy problems of the electro-weak theory.

    ↳ hep-thhep-phPLB(2017)·37 citations
42. 42*

    Correlation femtoscopy study at NICA and STAR energies within a viscous hydrodynamic plus cascade model

    P. Batyuk🇷🇺 · Iu. Karpenko🇮🇹 · R.Lednicky🇷🇺 · L.Malinina🇷🇺 · K.Mikhaylov🇷🇺 · O. Rogachevsky🇷🇺 · D.Wielanek🇵🇱

    Correlation femtoscopy allows one to measure the space-time characteristics of particle production in relativistic heavy-ion collisions due to the effects of quantum statistics (QS) and final state interactions (FSI). The main features of the femtoscopy measurements at top RHIC and LHC energies are considered as a manifestation of strong collective flow and are well interpreted within hydrodynamic models employing equation of state (EoS) with a crossover type transition between Quark-Gluon Plasma (QGP) and hadron gas phases. The femtoscopy at lower energies was intensively studied at AGS and SPS accelerators and is being studied now in the Beam Energy Scan program (BES) at the BNL Relativistic Heavy Ion Collider in the context of exploration of the QCD phase diagram. In this article we present femtoscopic observables calculated for Au-Au collisions at $\sqrt{s_{NN}}=7.7-62.4$ GeV in a viscous hydro + cascade model vHLLE+UrQMD and their dependence on the EoS of thermalized matter.

    ↳ nucl-thhep-exhep-phPRC(2017)·21 citations
43. 43*

    Experimental Evidence of Quantum Radiation Reaction in Aligned Crystals

    Tobias N. Wistisen🇩🇰 · Antonino Di Piazza🇩🇪 · Helge V. Knudsen🇩🇰 · Ulrik I. Uggerhøj🇩🇰

    Radiation reaction is the influence of the electromagnetic field emitted by a charged particle on the dynamics of the particle itself. Here we report experimental radiation emission spectra from ultrarelativistic positrons in silicon in a regime where both quantum and radiation-reaction effects dominate the dynamics of the positrons. We found that each positron emits multiple photons with energy comparable to its own energy, revealing the importance of quantum photon recoil. Moreover, the shape of the emission spectra indicates that photon emissions occur in a nonlinear regime where positrons absorb several quanta from the crystal field. Our theoretical analysis shows that only a full quantum theory of radiation reaction is capable of explaining the experimental results, with radiation-reaction effects arising from the recoils undergone by the positrons during multiple photon emissions. This experiment is the first fundamental test of quantum electrodynamics in a new regime where the dynamics of charged particles is determined not only by the external electromagnetic fields but also by the radiation-field generated by the charges themselves. Future experiments carried out in the same line will be able to, in principle, also shed light on the fundamental question about the structure of the electromagnetic field close to elementary charges.

    ↳ hep-exhep-phphysics.plasm-phNature Commun.(2018)·105 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.