Fri·Dec 18, 2020Friday·December 18, 2020

1. 01*

   Flavor changing top decays to charm and Higgs with $\tau \tau$ at the LHC

   Phillip Gutierrez🇺🇸 · Rishabh Jain🇺🇸 · Chung Kao🇺🇸

   We investigate the prospects of discovering the top quark decay into a charm quark and a Higgs boson ($t\to c{h}^0$) in top quark pair production at the CERN Large Hadron Collider (LHC). A general two Higgs doublet model is adopted to study flavor changing neutral Higgs (FCNH) interactions. We perform a parton level analysis as well as Monte Carlo simulations using \textsc{Pythia}~8 and \textsc{Delphes} to study the flavor changing top quark decay $t\to c{h}^0$, followed by the Higgs decaying into ${\tau }^{+}{\tau }^{-}$, with the other top quark decaying to a bottom quark ($b$) and two light jets ($t\to bW\to bjj$). To reduce the physics background to the Higgs signal, only the leptonic decays of tau leptons are used, ${\tau }^{+}{\tau }^{-}\to e^{\pm }{\mu }^{\mp }+\text{slashed}{E}_T$, where $\text{slashed}{E}_T$ represents the missing transverse energy from the neutrinos. In order to reconstruct the Higgs boson and top quark masses as well as to effectively remove the physics background, the collinear approximation for the highly boosted tau decays is employed. Our analysis suggests that a high energy LHC at $\sqrt{s}=27$ TeV will be able to discover this FCNH signal with an integrated luminosity $\mathcal{L}=3$ ab${}^{-1}$ for a branching fraction $\mathcal{B}(t\to c{h}^0)\text{agt}1.4\times 10^{-4}$ that corresponds to a FCNH coupling $|{\lambda }_{tch}|\text{agt}0.023$. This FCNH coupling is significantly below the current ATLAS combined upper limit of $|{\lambda }_{tch}|=0.064$.

   hep-phPRD(2021)·9 citations
2. 02*

   Disentangling observable dependence in SCETI and SCETII anomalous dimensions: angularities at two loops

   Christian W. Bauer🇺🇸 · Aneesh V. Manohar🇺🇸 · Pier Francesco Monni🇨🇭

   The resummation of radiative corrections to collider jet observables using soft collinear effective theory is encoded in differential renormalization group equations (RGEs), with anomalous dimensions depending on the observable under consideration. This observable dependence arises from the ultraviolet (UV) singular structure of real phase space integrals in the effective field theory. We show that the observable dependence of anomalous dimensions in SCETI problems can be disentangled by introducing a suitable UV regulator in real radiation integrals. Resummation in the presence of the new regulator can be performed by solving a two-dimensional system of RGEs in the collinear and soft sectors, and resembles many features of resummation in SCETII theories by means of the rapidity renormalization group. We study the properties of SCETI with the additional regulator and explore the connection with the system of RGEs in SCETII theories, highlighting some universal patterns that can be exploited in perturbative calculations. As an application, we compute the two-loop soft and jet anomalous dimensions for a family of recoil-free angularities and give new analytic results. This allows us to study the relations between the SCETI and SCETII limits for these observables. We also discuss how the extra UV regulator can be exploited to calculate anomalous dimensions numerically, and the prospects for numerical resummation.

   hep-phJHEP(2021)·14 citations
3. 03*

   Search for Light Exotic Fermions in Double-Beta Decays

   Matteo Agostini🇬🇧 · Elisabetta Bossio🇩🇪 · Alejandro Ibarra🇩🇪 · Xabier Marcano🇩🇪

   The Standard Model of Particle Physics predicts the double-$\beta$ decay of certain nuclei with the emission of two active neutrinos. In this letter, we argue that double-$\beta$ decay experiments could be used to probe models with light exotic fermions through the search for spectral distortions in the electron spectrum with respect to the Standard Model expectations. We consider two concrete examples: models with light sterile neutrinos, singly produced in the double-$\beta$ decay, and models with a light $Z_2$-odd fermion, pair produced due to a $Z_2$ symmetry. We estimate the discovery potential of a selection of double-$\beta$ decay experiments and find that future searches will test for the first time a new part of the parameter space of interest at the MeV-mass scale.

   hep-phhep-exnucl-exPLB(2021)·22 citations
4. 04*

   KKMC-hh for Precision Electroweak Phenomenology at the LHC

   Scott A. Yost🇺🇸 · Matthew Dittrich🇺🇸 · Stanislaw Jadach🇵🇱 · B.F.L. Ward🇺🇸 · Zbigniew Wąs🇵🇱

   We describe the program KKMC-hh, which calculates Z boson processes in hadronic collisions using coherent exclusive exponentiation (CEEX) with exact second-order photonic corrections at next-to-leading log and first-order weak vertex corrections, including initial and final state photonic radiation and initial-final interference. We describe current applications to precision forward-backward asymmetry calculations for the measurement of the electroweak mixing angle at the LHC.

   hep-phPoS(2021)·4 citations
5. 05*

   Trace anomaly contribution to hydrogen atom mass

   Bao-dong Sun🇨🇳 · Ze-hao Sun🇨🇳 · Jian Zhou🇨🇳

   We compute trace anomaly contribution to hydrogen atom mass, which turns out to be related to the part of the Lamb shift. This finding might shed new light on our understandings of the mass structure of QCD bound states, such as, proton.

   hep-phPRD(2021)·14 citations
6. 06*

   Review on Dark Matter Tools

   Chiara Arina🇧🇪

   Whilst the need for dark matter was established almost a century ago, only its gravitational interaction has been confirmed so far, allowing for plethora of models for dark matter. The Weakly Interacting Massive Particles (WIMPs) category has received by far the biggest attention, however despite the enormous experimental efforts, these particles remain elusive. The attention of the community has hence moved on to investigate the dark matter landscape over a much larger number of models with varying degrees of resemblances and differences in their predictions. This calls for the need to organise the various facets of dark matter models and their signatures, in order to maximise the experimental sensitivity and to select the models which are compatible with existing data. In this paper, I provide a short review of the most widespread public codes capable of computing dark matter observables. In particular, I discuss what is the status of each numerical tool in terms of: (i) capturing the WIMP phenomenology and (ii) accounting for new trend dark sector models that might be weakly coupled to ordinary matter and/or be strongly self-interacting. This short review has the aim of guiding the user towards selecting the best suited public code to confront his/her model with the largest variety of theoretical predictions and experimental data in order to determine the parameter space consistent with observations for his/her favourite dark matter model.

   hep-phastro-ph.COPoS(2021)·9 citations
7. 07*

   Composite Higgs revealed in Higgs pair photo-production at future colliders

   A. Bharucha🇫🇷 · G. Cacciapaglia🇫🇷 · A. Deandrea🇫🇷 · N. Gaur🇮🇳 · D. Harada🇯🇵 · F. Mahmoudi🇫🇷 · K. Sridhar🇮🇳

   The next generation electron-positron colliders are designed for precision studies of the Standard Model and its extensions, in particular in the Higgs sector. We consider the potential for discovery of composite Higgs models in Higgs pair production through photon collisions. This process is loop-generated, thus it provides access to all Higgs couplings and can show new physics effects in polarized and unpolarized cross-sections starting at relatively low collider energies. It is, therefore, relevant for all electron-positron colliders planned or in preparation. Sizeable deviations from the Standard Model predictions are present in a general class of composite Higgs models, as couplings of one or more Higgs bosons to fermions, or fermionic and scalar resonances, modify the destructive interference present in the Standard Model. In particular, large effects are due to the new quartic coupling of the Higgs to tops and to the presence of a light scalar resonance.

   hep-phJHEP(2021)·6 citations
8. 08*

   Dispersion of neutrinos in a medium

   Ki-Young Choi🇰🇷 · Eung Jin Chun🇰🇷 · Jongkuk Kim🇰🇷

   We analyze the dispersion relations of Weyl or Majorana, and Dirac neutrinos in a complex scalar medium which interacts with the neutrinos through Yukawa couplings. They are solved by perturbative calculation in various limits representing different physical situations, some of which allow the medium-induced neutrino oscillation to occur. Remarkably, peculiar dispersion relations arise differently for Majorana or Dirac neutrinos in the non-relativistic limit. This provides an unpleasant restriction on the cosmological scenario of a scalar dark matter coupling to neutrinos. At present, the model parameter space is constrained by the neutrino scattering with dark matter through astrophysical neutrino observations.

   hep-ph19 citations
9. 09*

   Nonleptonic $K\to 2\pi$ decay dynamics

   Hector Gisbert🇩🇪

   Using Chiral Perturbation Theory to properly account for the dynamics of nonleptonic $K\to 2\pi$ decays, we found the Standard Model prediction for the CP violating ratio $\text{mbox}Re\left({\epsilon }^{\prime }/\epsilon \right)=\left(14\pm 5\right)\times 10^{-4}$, where isospin breaking effects are included, in perfect agreement with the current experimental world average. Similar results have been reported by a recent release of improved lattice data.

   hep-phhep-exhep-latNucl.Part.Phys.Proc.(2021)·7 citations
10. 10*

    Origin of Strong Linear Polarization from Fast Radio Bursts

    Runna Wang🇨🇳 · Siming Liu🇨🇳 · Anda Xiong🇬🇧 · Qi-Hui Chen🇨🇳 · Fengrong Zhu🇨🇳

    The detection of almost 100% linearly polarized emission from the fast radio burst source FRB 121102 implies coherent emission of relativistic electrons moving in perpendicular to the ambient magnetic field. The origin of such a particle distribution is very intriguing. Given that FRB 121102 is likely driven by a neutron star, we explored orbits of charged particles trapped in a dipole magnetic field (the Störmer problem). Most previous studies focused on particles with relatively low energies so that the guiding center approximation may be applied. High energy particles usually have chaotic orbits except those on a periodic orbit or near stable periodic orbits. Via evaluation of the maximum Lyapunov exponent of orbits of particles launched from the equatorial plane with an axial velocity (the angular velocity sets the length and energy scales of the system), we found prominent regions of quasi-periodic orbits around stable periodic orbits in the equatorial plane at high-energies. Particles in these orbits oscillate around the equatorial plane and their radial distance from the dipole can vary by a factor of/,2. Relativistic electrons in such orbits may be responsible for the almost 100% polarized emission from FRB 121102.

    hep-phApJ(2021)·2 citations
11. 11*

    Leading-order QED radiative corrections to timelike Compton scattering on the proton

    Matthias Heller🇩🇪 · Niklas Keil🇩🇪 · Marc Vanderhaeghen🇩🇪

    We evaluate the leading-order QED radiative corrections to the timelike Compton scattering (TCS) process $\gamma p\to l^{-}{l}^{+}p$. We study these corrections in two energy regimes using different models for the TCS amplitude. In the low-energy regime we calculate the contribution due to the proton and its lowest-energy excitation, the $\Delta (1232)$ resonance. In the high-energy near-forward kinematical regime we calculate the TCS amplitude in a handbag approach in terms of Generalized Parton Distributions (GPDs). On the level of cross sections we find the QED radiative corrections to be in the $5-10\%$ range in the low-energy regime and around $20\%$ in the high-energy regime. We show that in both the di-lepton forward-backward asymmetry as well as in the photon beam helicity asymmetry these corrections nearly cancel out, making them gold-plated observables to extract the real and imaginary parts of the TCS amplitude. We demonstrate in particular the sensitivity of these asymmetries on GPD parameterizations for a recent CLAS12@JLab TCS experiment.

    hep-phnucl-thPRD(2021)·6 citations
12. 12*

    Soft-drop grooming for hadronic event shapes

    Jeremy Baron🇺🇸 · Daniel Reichelt🇩🇪 · Steffen Schumann🇩🇪 · Niklas Schwanemann🇩🇪 · Vincent Theeuwes🇩🇪

    Soft-drop grooming of hadron-collision final states has the potential to significantly reduce the impact of non-perturbative corrections, and in particular the underlying-event contribution. This eventually will enable a more direct comparison of accurate perturbative predictions with experimental measurements. In this study we consider soft-drop groomed dijet event shapes. We derive general results needed to perform the resummation of suitable event-shape variables to next-to-leading logarithmic (NLL) accuracy matched to exact next-to-leading order (NLO) QCD matrix elements. We compile predictions for the transverse-thrust shape accurate to NLO+NLL' using the implementation of the CAESAR formalism in the Sherpa event generator framework. We complement this by state-of-the-art parton- and hadron-level predictions based on NLO QCD matrix elements matched with parton showers. We explore the potential to mitigate non-perturbative corrections for particle-level and track-based measurements of transverse thrust by considering a wide range of soft-drop parameters. We find that soft-drop grooming indeed is very efficient in removing the underlying event. This motivates future experimental measurements to be compared to precise QCD predictions and employed to constrain non-perturbative models in Monte-Carlo simulations.

    hep-phhep-exJHEP(2021)·34 citations
13. 13*

    Quantum interference effects in Higgs boson pair-production beyond the Standard Model

    Biswaranjan Das🇷🇼 · Stefano Moretti🇬🇧 · Shoaib Munir🇷🇼 · Poulose Poulose🇮🇳

    New physics frameworks like the Next-to-Minimal Supersymmetric Standard Model and the Next-to-2-Higgs-doublet Model contain three neutral CP-even Higgs bosons. It is possible for the heavier two of these states to have masses identical to each other, which can result in a sizeable quantum interference between their propagators in processes they mediate. For both these models, we study the impact of such interference on the pair-production of the lightest of the three scalars, which we identify with the observed 125 GeV Higgs boson, in the gluon-fusion channel at the Large Hadron Collider (LHC). We find that the inclusion of these effects can substantially alter the cross section, compared to its value when they are ignored, for this process. Our results illustrate the importance of taking possible quantum interference effects into account not only when investigating the phenomenology of extended Higgs sectors at the future Run(s) of the LHC, but also when imposing its current exclusion bounds on the parameter spaces of these models.

    hep-phEPJC(2021)·6 citations
14. 14*

    Bargmann Invariants, Geometric Phases and Recursive Parametrization with Majorana Fermions

    Rohan Pramanick🇮🇳 · Swarup Sangiri🇮🇳 · Utpal Sarkar🇮🇳

    A generalized connection between the quantum mechanical Bargmann invariants and the geometric phases was established for the Dirac fermions. We extend that formalism for the Majorana fermions by defining proper quantum mechanical ray and Hilbert spaces. We then relate both the Dirac and Majorana type Bargmann invariants to the rephasing invariant measures of CP violation with the Majorana neutrinos, assuming that the neutrinos have lepton number violating Majorana masses. We then generalize the recursive parametrization for studying any unitary matrices to include the Majorana fermions, which could be useful for studying the neutrino mixing matrix.

    hep-phNPB(2021)·1 citation
15. 15*

    Multiperipheral final states in crowded twin-jet events at the LHC

    N. Bethencourt de León🇪🇸 · G. Chachamis🇵🇹 · A. Sabio Vera🇪🇸

    The 13 TeV run of the LHC has provided a unique opportunity to explore multi-jet final states with unprecedented accuracy. An interesting region for study is that of events where one jet is tagged in the forward direction and another one in the backward direction and a plethora of low energy mini-jets populate the possibly large rapidity span in between them. Since the number of these events is very high, it is possible to introduce stringent constraints on the transverse momentum of the two leading jets which can be kept in small windows not very different from each other, defining what we call "twin jets". The associated "crowd" of mini-jets can also have a restricted span in transverse momentum. The study of these events for a fixed multiplicity is an ideal playground to investigate different models of multi-particle production in hadron-hadron collisions. We set up an exploratory analysis by using an ancient model of Chew and Pignotti to describe the gross features one can expect for the structure of single and double differential-in-rapidity cross sections and for particle-particle rapidity correlations when the longitudinal phase space completely decouples from the transverse degrees of freedom.

    hep-phNPB(2021)·10 citations
16. 16*

    Unitarity in KK-graviton production: A case study in warped extra-dimensions

    A. de Giorgi🇩🇪 · S. Vogl🇩🇪

    The Kaluza-Klein (KK) decomposition of higher-dimensional gravity gives rise to a tower of KK-gravitons in the effective four-dimensional (4D) theory. Such massive spin-2 fields are known to be connected with unitarity issues and easily lead to a breakdown of the effective theory well below the naive scale of the interaction. However, the breakdown of the effective 4D theory is expected to be controlled by the parameters of the 5D theory. Working in a simplified Randall-Sundrum model we study the matrix elements for matter annihilations into massive gravitons. We find that truncating the KK-tower leads to an early breakdown of perturbative unitarity. However, by considering the full tower we obtain a set of sum rules for the couplings between the different KK-fields that restore unitarity up to the scale of the 5D theory. We prove analytically that these are fulfilled in the model under consideration and present numerical tests of their convergence. This work complements earlier studies that focused on graviton self-interactions and yields additional sum rules that are required if matter fields are incorporated into warped extra-dimensions.

    hep-phJHEP(2021)·19 citations
17. 17*

    A Near-Conformal Composite Higgs Model

    Thomas Appelquist🇺🇸 · James Ingoldby🇮🇹 · Maurizio Piai🇬🇧

    We analyze a composite Higgs model based on the confining $SU(3)$ gauge theory with $N_f=8$ Dirac fermions in the fundamental representation. This gauge theory has been studied on the lattice and shown to be well described by a dilaton effective field theory (EFT). Here we modify the EFT by assigning standard-model quantum numbers such that four of the composite pseudo-Nambu-Goldstone boson (pNGB) fields form the standard-model Higgs doublet, by coupling it to the top quark, and by adding to the potential a term that triggers electroweak symmetry breaking. The model contains a pNGB Higgs boson, a set of heavier pNGBs, and an approximate dilaton in the same mass range. We study the phenomenology of the model, and discuss the amount of tuning required to insure consistency with current direct and indirect bounds on new physics, highlighting the role of the dilaton field.

    hep-phhep-latPRL(2021)·53 citations
18. 18*

    Unified Emergence of Energy Scales and Cosmic Inflation

    Jisuke Kubo🇩🇪 · Jeffrey Kuntz🇩🇪 · Manfred Lindner🇩🇪 · Jonas Rezacek🇩🇪 · Philipp Saake🇩🇪 · Andreas Trautner🇩🇪

    In the quest for unification of the Standard Model with gravity, classical scale invariance can be utilized to dynamically generate the Planck mass $M_{\mathrm{Pl}}$. Then, the relation of Planck scale physics to the scale of electroweak symmetry breaking ${\mu }_H$ requires further explanation. In this paper, we propose a model that uses the spontaneous breaking of scale invariance in the scalar sector as a unified origin for dynamical generation of both scales. Using the Gildener-Weinberg approximation, only one scalar acquires a vacuum expectation value of $v_S\sim (10^{16-17})\mathrm{GeV}$, thus radiatively generating $M_{\mathrm{Pl}}\approx {\beta }_S^{1/2}{v}_S$ and ${\mu }_H$ via the neutrino option with right handed neutrino masses $m_N=y_M{v}_S\sim 10^7\mathrm{GeV}$. Consequently, active SM neutrinos are given a mass with the inclusion of a type-I seesaw mechanism. Furthermore, we adopt an unbroken $Z_2$ symmetry and a $Z_2$-odd set of right-handed Majorana neutrinos $\chi$ that do not take part in the neutrino option and are able to produce the correct dark matter relic abundance (dominantly) via inflaton decay. The model also describes cosmic inflation and the inflationary CMB observables are predicted to interpolate between those of $R^2$ and linear chaotic inflationary model and are thus well within the strongest experimental constraints.

    hep-phastro-ph.COgr-qcJHEP(2021)·30 citations
19. 19*

    Flavoured Warped Axion

    Quentin Bonnefoy🇩🇪 · Peter Cox🇦🇺 · Emilian Dudas🇫🇷 · Tony Gherghetta🇺🇸 · Minh D. Nguyen🇺🇸

    We consider a 5D extension of the DFSZ axion model that addresses both the axion quality and fermion mass hierarchy problems, and predicts flavour-dependent, off-diagonal axion-fermion couplings. The axion is part of a 5D complex scalar field charged under a U(1)${}_{PQ}$ symmetry that is spontaneously broken in the bulk, and is insensitive to explicit PQ breaking on the UV boundary. Bulk Standard Model fermions interact with two Higgs doublets that can be localized on the UV boundary or propagate in the bulk to explain the fermion masses and mixings. When the Higgs doublets are localized on the UV boundary, they induce flavour diagonal couplings between the fermions and the axion. However, when the Higgs doublets propagate in the bulk, the overlap of the axion and fermion profiles generates flavour off-diagonal couplings. The effective scale of these off-diagonal couplings in both the quark and lepton sectors can be as small as $10^{11}$ GeV, and therefore will be probed in future precision flavour experiments.

    hep-phhep-thJHEP(2021)·31 citations
20. 20*

    New Strong Bounds on sub-GeV Dark Matter from Boosted and Migdal Effects

    Victor V. Flambaum🇦🇺 · Liangliang Su🇨🇳 · Lei Wu🇨🇳 · Bin Zhu🇨🇳

    Due to the low nuclear recoils, sub-GeV dark matter (DM) is usually beyond the sensitivity of the conventional DM direct detection experiments. The boosted and Migdal scattering mechanisms have been proposed as two new complementary avenues to search for light DM. In this work, we consider the momentum-transfer effect in the DM-nucleus scattering to derive the new bounds on sub-GeV DM for these two scenarios. We show that such an effect is sizable so that the existing bounds on the DM-nucleus scattering cross section can be improved significantly.

    hep-phastro-ph.COSCPMA(2023)·60 citations
21. 21*

    Electroweak Phase Transition with an SU(2) Dark Sector

    Tathagata Ghosh🇧🇷 · Huai-Ke Guo🇺🇸 · Tao Han🇺🇸 · Hongkai Liu🇺🇸

    We consider a non-Abelian dark SU(2)${}_{\mathrm{D}}$ model where the dark sector couples to the Standard Model (SM) through a Higgs portal. We investigate two different scenarios of the dark sector scalars with $Z_2$ symmetry, with Higgs portal interactions that can introduce mixing between the SM Higgs boson and the SM singlet scalars in the dark sector. We utilize the existing collider results of the Higgs signal rate, direct heavy Higgs searches, and electroweak precision observables to constrain the model parameters. The ${\text{SU(2)}}_{\text{D}}$ partially breaks into ${\text{U(1)}}_{\text{D}}$ gauge group by the scalar sector. The resulting two stable massive dark gauge bosons and pseudo-Goldstone bosons can be viable cold dark matter candidates, while the massless gauge boson from the unbroken ${\text{U(1)}}_{\text{D}}$ subgroup is a dark radiation and can introduce long-range attractive dark matter (DM) self-interaction, which can alleviate the small-scale structure issues. We study in detail the pattern of strong first-order phase transition and gravitational wave (GW) production triggered by the dark sector symmetry breaking, and further evaluate the signal-to-noise ratio for several proposed space interferometer missions. We conclude that the rich physics in the dark sector may be observable with the current and future measurements at colliders, DM experiments, and GW interferometers.

    hep-phastro-ph.COJHEP(2021)·50 citations
22. 22*

    Predicting the ${\bar{D}}_s^{(\ast )}{D}_s^{(\ast )}$ bound states as the partners of $X(3872)$

    Lu Meng🇩🇪 · Bo Wang🇨🇳 · Shi-Lin Zhu🇨🇳

    In this work, we investigate the SU(3) flavor symmetry, heavy quark spin symmetry and their breaking effects in the di-meson systems. We prove the existence of the $[{\bar{D}}_s^{\ast }{D}_s^{\ast }{]}^{0^{++}}$, $[{\bar{D}}_s^{\ast }{D}_s/{\bar{D}}_s^{}{D}_s^{\ast }{]}^{1^{+-}}$, and $[{\bar{D}}_s^{\ast }{D}_s^{\ast }{]}^{1^{+-}}$ bound states as the consequence of two prerequisites in the SU(3) flavor symmetry and heavy quark spin symmetry. The first prerequisite, the $X(3872)$ as the weakly ${\bar{D}}^{\ast }D/\bar{D}{D}^{\ast }$ bound state is supported by its mass and decay branching ratios. The second prerequisite, the existence of the $[{\bar{D}}_s{D}_s{]}^{0^{++}}$ bound state is supported by the lattice QCD calculation [arXiv:2011.02542(hep-lat)] and the observation of ${\chi }_{c0}(3930)$ by the LHCb Collaboration[Phys.Rev.Lett.125,242001, Phys.Rev.D102,112003]. We hope the future experimental analyses can search for these bound states in the $B\to D_{(s)}^{(\ast )}{\bar{D}}_{(s)}^{(\ast )}h$ processes ($h$ denotes the light hadrons). The $[{\bar{D}}_s^{\ast }{D}_s^{\ast }{]}^{0^{++}}$ bound state is also expected to be reconstructed in the $J/\psi \varphi$ final state in the $B\to J/\psi \varphi K$ decay.

    hep-phhep-exhep-latSci.Bull.(2021)·39 citations
23. 23*

    Searching for Lepton Flavour (Universality) Violation and Collider Signals from a Singly-Charged Scalar Singlet

    Andreas Crivellin🇨🇭 · Fiona Kirk🇨🇭 · Claudio Andrea Manzari🇨🇭 · Luca Panizzi🇸🇪

    In recent years, evidence for lepton flavour universality violation beyond the Standard Model has been accumulated. In this context, a singly charged $SU(2{)}_L$ singlet scalar (${\varphi }^{\pm }$) is very interesting, as it can only have flavour off-diagonal couplings to neutrinos and charged leptons, therefore necessarily violating lepton flavour (universality). In fact, it gives a (necessarily constructive) tree-level effect in $\ell \to {\ell }^{\prime }\nu \nu$ processes, while contributing to charged lepton flavour violating only at the loop-level. Therefore, it can provide a common explanation of the hints for new physics in $\tau \to \mu \nu \nu /\tau (\mu )\to e\nu \nu$ and of the Cabibbo Angle Anomaly. Such an explanation predicts $\mathrm{Br}[\tau \to e\gamma ]$ to be of the order of a few times $10^{-11}$ while $\mathrm{Br}[\tau \to e\mu \mu ]$ can be of the order of $10^{-9}$ for order one couplings and therefore in the reach of forthcoming experiments. Furthermore, we derive a {novel} coupling-independent lower limit on the scalar mass of $\approx 200$GeV by recasting LHC slepton searches. In the scenario preferred by low energy precision data, the lower limit is even strengthened to $\approx 300$GeV, showing the complementary between LHC searches and flavour observables. Furthermore, we point out that this model can be tested by reinterpreting DM mono-photon searches at future $e^{+}{e}^{-}$ colliders.

    hep-phhep-exnucl-exnucl-thPRD(2021)·66 citations
24. 24*

    Cosmological and astrophysical probes of dark baryons

    David McKeen🇨🇦 · Maxim Pospelov🇺🇸 · Nirmal Raj🇨🇦

    We examine the cosmological and astrophysical signatures of a "dark baryon," a neutral fermion that mixes with the neutron. As the mixing is through a higher-dimensional operator at the quark level, production of the dark baryon at high energies is enhanced so that its abundance in the early universe may be significant. Treating its initial abundance as a free parameter, we derive new, powerful limits on the properties of the dark baryon. Primordial nucleosynthesis and the cosmic microwave background provide strong constraints due to the inter-conversion of neutrons to dark baryons through their induced transition dipole, and due to late decays of the dark baryon. Additionally, neutrons in a neutron star could decay slowly to dark baryons, providing a novel source of heat that is constrained by measurements of pulsar temperatures. Taking all the constraints into account, we identify parameter space where the dark baryon can be a viable dark matter candidate and discuss promising avenues for probing it.

    hep-phastro-ph.COastro-ph.HEhep-exPRD(2021)·46 citations
25. 25*

    Bounds on warm dark matter from Schwarzschild primordial black holes

    Jérémy Auffinger🇫🇷 · Isabella Masina🇮🇹 · Giorgio Orlando🇳🇱

    We consider light dark matter candidates originated from the evaporation of Schwarzschild primordial black holes, with masses in the range $10^{-5}-10^9$ g. These candidates are beyond Standard Model particles with negligible couplings to the other particles, so that they interact only gravitationally. Belonging to the category of warm dark matter, they nevertheless spoil structure formation, with a softer impact for increasing values of the candidate spin. Requiring such candidates to fully account for the observed dark matter, we find that the scenario of black hole domination is ruled out for all spin values up to 2. For the scenario of radiation domination, we derive upper limits on the parameter $\beta$ (the primordial black hole energy density at formation over the radiation one), which are less stringent the higher the candidate spin is.

    hep-phastro-ph.COastro-ph.HEhep-thEur.Phys.J.Plus(2021)·66 citations
26. 26*

    New Physics effects in leptonic and semileptonic decays

    Damir Bečirević🇫🇷 · Florentin Jaffredo🇫🇷 · Ana Peñuelas🇩🇪 · Olcyr Sumensari🇨🇭

    We discuss the possibilities of extracting the constraints on New Physics by using the current data on the leptonic and semileptonic decays of pseudoscalar mesons. In doing so we use a general low energy Lagrangian that besides the vector and axial operators also includes the (pseudo-)scalar and tensor ones. In obtaining constraints on New Physics couplings we combine the experimental information concerning several decay modes with the accurate lattice QCD results for the hadronic matrix elements. We propose to study new observables that can be extracted from the angular analysis of the semileptonic decays and discuss their values both in the Standard Model and in some specific scenarios of physics beyond the Standard Model.

    hep-phJHEP(2021)·57 citations
27. 27*

    Measuring QCD Splittings with Invertible Networks

    Sebastian Bieringer🇩🇪 · Anja Butter🇩🇪 · Theo Heimel🇩🇪 · Stefan Höche🇺🇸 · Ullrich Köthe🇩🇪 · Tilman Plehn🇩🇪 · Stefan T. Radev🇩🇪

    QCD splittings are among the most fundamental theory concepts at the LHC. We show how they can be studied systematically with the help of invertible neural networks. These networks work with sub-jet information to extract fundamental parameters from jet samples. Our approach expands the LEP measurements of QCD Casimirs to a systematic test of QCD properties based on low-level jet observables. Starting with an toy example we study the effect of the full shower, hadronization, and detector effects in detail.

    hep-phSciPost Phys.(2021)·47 citations
28. 28*

    Simple and statistically sound recommendations for analysing physical theories

    Shehu S. AbdusSalam🇮🇷 · Fruzsina J. Agocs🇬🇧 · Benjamin C. Allanach🇬🇧 · Peter Athron🇦🇺 · Csaba Balázs🇦🇺 · Emanuele Bagnaschi🇨🇭 · Philip Bechtle🇩🇪 · Oliver Buchmueller🇬🇧 · Ankit Beniwal🇧🇪 · Jihyun Bhom🇵🇱 · Sanjay Bloor🇬🇧 · Torsten Bringmann🇳🇴 and 63 other authors

    Physical theories that depend on many parameters or are tested against data from many different experiments pose unique challenges to statistical inference. Many models in particle physics, astrophysics and cosmology fall into one or both of these categories. These issues are often sidestepped with statistically unsound ad hoc methods, involving intersection of parameter intervals estimated by multiple experiments, and random or grid sampling of model parameters. Whilst these methods are easy to apply, they exhibit pathologies even in low-dimensional parameter spaces, and quickly become problematic to use and interpret in higher dimensions. In this article we give clear guidance for going beyond these procedures, suggesting where possible simple methods for performing statistically sound inference, and recommendations of readily-available software tools and standards that can assist in doing so. Our aim is to provide any physicists lacking comprehensive statistical training with recommendations for reaching correct scientific conclusions, with only a modest increase in analysis burden. Our examples can be reproduced with the code publicly available at https://doi.org/10.5281/zenodo.4322283.

    hep-phastro-ph.COhep-exphysics.data-anRept.Prog.Phys.(2022)·35 citations
29. 29*

    Matter-antimatter asymmetry and non-inertial effects

    V. M. G. Silveira🇧🇷 · C. A. Z. Vasconcellos🇧🇷 · E. G. S. Luna🇧🇷 · D. Hadjimichef🇧🇷

    We investigate non-inertial effects on $CP$-violating processes using a model, based on the framework of quantum field theory in curved spacetimes, devised to account for the decay of accelerated particles. We show that the $CP$ violation parameter for the decay of accelerated kaons into two pions decreases very slightly as very high accelerations are achieved, implying decreased asymmetry between matter and antimatter in this regime. We discuss the relationship between these results and cosmological processes surrounding matter-antimatter asymmetry and argue that, due to the connection between non-inertial and thermal phenomena established by the Unruh effect, this kind of computation may prove useful in furthering the understanding of thermodynamical effects in curved spacetimes.

    ↳ gr-qchep-phJHEP(2020)·1 citation
30. 30*

    Determining the range of validity of quasar X-ray and UV flux measurements for constraining cosmological model parameters

    Narayan Khadka🇺🇸 · Bharat Ratra🇺🇸

    We use six different cosmological models to study the recently-released compilation of X-ray and UV flux measurements of 2038 quasars (QSOs) which span the redshift range $0.009\le z\le 7.5413$. We find, for the full QSO data set, that the parameters of the X-ray and UV luminosities $L_X-L_{UV}$ relation used to standardized these QSOs depend on the cosmological model used to determine these parameters, i.e, it appears that the full QSO data set include QSOs that are not standardized and so cannot be used for the purpose of constraining cosmological parameters. Subsets of the QSO data, restricted to redshifts $z\lesssim 1.5-1.7$ obey the $L_X-L_{UV}$ relation in a cosmological-model-independent manner, and so can be used to constrain cosmological parameters. The cosmological constraints from these lower-$z$, smaller QSO data subsets are mostly consistent with, but significantly weaker than, those that follow from baryon acoustic oscillation and Hubble parameter measurements.

    ↳ astro-ph.COgr-qchep-phhep-thMNRAS(2021)·90 citations
31. 31*

    Propagation of quantum gravity-modified gravitational waves on a classical FLRW spacetime

    Angel Garcia-Chung🇲🇽 · James B. Mertens🇺🇸 · Saeed Rastgoo🇨🇦 · Yaser Tavakoli🇮🇷 · Paulo Vargas Moniz🇵🇹

    The linearized Einstein field equations provide a low-energy wave equation for the propagation of gravitational fields which may originate from a high energy source. Motivated by loop quantum gravity, we propose the polymer quantization scheme to derive the effective propagation of such waves on a classical Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime. To overcome the challenge of polymer quantizing a time-dependent Hamiltonian, we rewrite such a Hamiltonian in a time-independent manner in the extended phase space, polymerize it, and then transform it back to the usual phase space. In this way we obtain a time-dependent polymer Hamiltonian for the gravitational waves. We then derive the effective equations of motion and show that (i) the form of the waves is modified, (ii) the speed of the waves depends on their frequencies, and (iii) quantum effects become more apparent as waves traverse longer distances.

    ↳ gr-qcastro-ph.HEhep-phhep-thPRD(2021)·23 citations
32. 32*

    Siegel modular flavor group and CP from string theory

    Alexander Baur🇩🇪 · Moritz Kade🇩🇪 · Hans Peter Nilles🇩🇪 · Saul Ramos-Sanchez🇲🇽 · Patrick K.S. Vaudrevange🇩🇪

    We derive the potential modular symmetries of heterotic string theory. For a toroidal compactification with Wilson line modulus, we obtain the Siegel modular group $\mathrm{Sp}(4,\mathbb{Z})$ that includes the modular symmetries $\mathrm{SL}(2,\mathbb{Z}{)}_T$ and $\mathrm{SL}(2,\mathbb{Z}{)}_U$ (of the "geometric" moduli $T$ and $U$) as well as mirror symmetry. In addition, string theory provides a candidate for a CP-like symmetry that enhances the Siegel modular group to $\mathrm{GSp}(4,\mathbb{Z})$.

    ↳ hep-thhep-phPLB(2021)·51 citations
33. 33*

    Regulator dependence of inhomogeneous phases in the 2+1-dimensional Gross-Neveu model

    Michael Buballa🇩🇪 · Lennart Kurth🇩🇪 · Marc Wagner🇩🇪 · Marc Winstel🇩🇪

    The phase diagram of the Gross-Neveu model in $2+1$ space-time dimensions at non-zero temperature and chemical potential is studied in the limit of infinitely many flavors, focusing on the possible existence of inhomogeneous phases, where the order parameter $\sigma$ is non-uniform in space. To this end, we analyze the stability of the energetically favored homogeneous configuration $\sigma (\text{x})=\bar{\sigma }=\text{const}$ with respect to small inhomogeneous fluctuations, employing lattice field theory with two different lattice discretizations as well as a continuum approach with Pauli-Villars regularization. Within lattice field theory, we also perform a full minimization of the effective action, allowing for arbitrary 1-dimensional modulations of the order parameter. For all methods special attention is paid to the role of cutoff effects. For one of the two lattice discretizations, no inhomogeneous phase was found. For the other lattice discretization and within the continuum approach with a finite Pauli-Villars cutoff parameter $\Lambda$, we find a region in the phase diagram where an inhomogeneous order parameter is favored. This inhomogeneous region shrinks, however, when $a$ is decreased or $\Lambda$ is increased, and finally diappears for all non-zero temperatures when the cutoff is removed completely. For vanishing temperature, we find hints for a degeneracy of homogeneous and inhomogeneous solutions, in agreement with earlier findings.

    ↳ hep-lathep-phPRD(2021)·38 citations
34. 34*

    Probing sub-eV Dark Matter decays with PTOLEMY

    Kyrylo Bondarenko🇨🇭 · Alexey Boyarsky🇳🇱 · Marco Nikolic🇦🇹 · Josef Pradler🇦🇹 · Anastasia Sokolenko🇦🇹

    When the Dark Matter mass is below the eV-scale, its cosmological occupation number exceeds the ones of photons from the cosmic microwave background as well as of relic neutrinos. If such Dark Matter decays to pairs of neutrinos, it implies that experiments that seek the detection of the cosmic neutrino background may as well be sensitive to this additional form of "dark radiation". Here we study the prospects for detection taking into account various options for the forecasted performance of the future PTOLEMY experiment. From a detailed profile likelihood analysis we find that Dark Matter decays with lifetime as large as $10^4$ Gyr or a sub-% Dark Matter fraction decaying today can be discovered. The prospects are facilitated by the distinct spectral event shape that is introduced from galactic and cosmological neutrino dark radiation fluxes. In the process we also clarify the importance of Pauli-blocking in the Dark Matter decay. The scenarios presented in this work can be considered early physics targets in the development of these instruments with relaxed demands on performance and energy resolution.

    ↳ astro-ph.COhep-phJCAP(2021)·11 citations
35. 35*

    Image-Based Jet Analysis

    Michael Kagan🇺🇸

    Image-based jet analysis is built upon the jet image representation of jets that enables a direct connection between high energy physics and the fields of computer vision and deep learning. Through this connection, a wide array of new jet analysis techniques have emerged. In this text, we survey jet image based classification models, built primarily on the use of convolutional neural networks, examine the methods to understand what these models have learned and what is their sensitivity to uncertainties, and review the recent successes in moving these models from phenomenological studies to real world application on experiments at the LHC. Beyond jet classification, several other applications of jet image based techniques, including energy estimation, pileup noise reduction, data generation, and anomaly detection, are discussed.

    ↳ physics.data-ancs.CVcs.LGhep-ex+113 citations
36. 36*

    Scattering of Goldstone Bosons and resonance production in a Composite Higgs model on the lattice

    Vincent Drach🇬🇧 · Tadeusz Janowski🇬🇧 · Claudio Pica🇩🇰 · Sasa Prelovsek🇸🇮

    We calculate the coupling between a vector resonance and two Goldstone bosons in $SU(2)$ gauge theory with $N_f=2$ Dirac fermions in the fundamental representation. The considered theory can be used to construct a minimal Composite Higgs models. The coupling is related to the width of the vector resonance and we determine it by simulating the scattering of two Goldstone bosons where the resonance is produced. The resulting coupling is $g_{\mathrm{VPP}}=7.8\pm 0.6$, not far from $g_{\rho \pi \pi }\simeq 6$ in QCD. This is the first lattice calculation of the resonance properties for a minimal UV completion. This coupling controls the production cross section of the lightest expected resonance at the LHC and enters into other tests of the Standard Model, from Vector Boson Fusion to electroweak precision tests. Our prediction is crucial to constrain the model using lattice input and for understanding the behavior of the vector meson production cross section as a function of the underlying gauge theory. We also extract the coupling $g_{\mathrm{VPP}}^{\mathrm{KSRF}}=9.4\pm 0.6$ assuming the vector-dominance and find that this phenomenological estimate slightly overestimates the value of the coupling.

    ↳ hep-lathep-phJHEP(2021)·28 citations
37. 37*

    Black Hole S-matrix for a scalar field

    Panos Betzios🇫🇷 · Nava Gaddam🇳🇱 · Olga Papadoulaki🇮🇹

    We describe a unitary scattering process, as observed from spatial infinity, of massless scalar particles on an asymptotically flat Schwarzschild black hole background. In order to do so, we split the problem in two different regimes governing the dynamics of the scattering process. The first describes the evolution of the modes in the region away from the horizon and can be analysed in terms of the effective Regge-Wheeler potential. In the near horizon region, where the Regge-Wheeler potential becomes insignificant, the WKB geometric optics approximation of Hawking's is replaced by the near-horizon gravitational scattering matrix that captures non-perturbative soft graviton exchanges near the horizon. We perform an appropriate matching for the scattering solutions of these two dynamical problems and compute the resulting Bogoliubov relations, that combines both dynamics. This allows us to formulate an S-matrix for the scattering process that is manifestly unitary. We discuss the analogue of the (quasi)-normal modes in this setup and the emergence of gravitational echoes that follow an original burst of radiation as the excited black hole relaxes to equilibrium.

    ↳ hep-thgr-qchep-phJHEP(2021)·26 citations
38. 38*

    Probing Small-Scale Power Spectra with Pulsar Timing Arrays

    Vincent S. H. Lee🇺🇸 · Andrea Mitridate🇺🇸 · Tanner Trickle🇺🇸 · Kathryn M. Zurek🇺🇸

    Models of Dark Matter (DM) can leave unique imprints on the Universe's small scale structure by boosting density perturbations on small scales. We study the capability of Pulsar Timing Arrays to search for, and constrain, subhalos from such models. The models of DM we consider are ordinary adiabatic perturbations in $\Lambda$CDM, QCD axion miniclusters, models with early matter domination, and vector DM produced during inflation. We show that $\Lambda$CDM, largely due to tidal stripping effects in the Milky Way, is out of reach for PTAs (as well as every other probe proposed to detect DM small scale structure). Axion miniclusters may be within reach, although this depends crucially on whether the axion relic density is dominated by the misalignment or string contribution. Models where there is matter domination with a reheat temperature below 1 GeV may be observed with future PTAs. Lastly, vector DM produced during inflation can be detected if it is lighter than $10^{-16}\mathrm{GeV}$. We also make publicly available a Python Monte Carlo tool for generating the PTA time delay signal from any model of DM substructure.

    ↳ astro-ph.COhep-phJHEP(2021)·87 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.