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CERN Document Server latest documents in Theoretical Physics (TH)enTue, 02 Jun 2015 11:29:08 GMTInvenio 1.1.3.1106-62468cds.support@cern.ch36013975125http://cds.cern.ch/img/site_logo_rss.pngCERN Document Server
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Aspects of Quadratic Gravity
http://cds.cern.ch/record/2020526
We discuss quadratic gravity where terms quadratic in the curvature tensor are included in the action. After reviewing the corresponding field equations, we analyze in detail the physical propagating modes in some specific backgrounds. First we confirm that the pure $R^2$ theory is indeed ghost free. Then we point out that for flat backgrounds the pure $R^2$ theory propagates only a scalar massless mode and no spin-two tensor mode. However, the latter emerges either by expanding the theory around curved backgrounds like de Sitter or anti-de Sitter, or by changing the long-distance dynamics by introducing the standard Einstein term. In both cases, the theory is modified in the infrared and a propagating graviton is recovered. Hence we recognize a subtle interplay between the UV and IR properties of higher order gravity. We also calculate the corresponding Newton's law for general quadratic curvature theories. Finally, we discuss how quadratic actions may be obtained from a fundamental theory like string- or M-theory. We demonstrate that string theory on non-compact $CY_3$ manifolds, like a line bundle over $\mathbb{CP}^2$, may indeed lead to gravity dynamics determined by a higher curvature action.Alvarez-Gaume, LuisKehagias, AlexKounnas, CostasLust, DieterRiotto, AntonioSat, 30 May 2015 07:36:56 GMT28 May 2015arXiv:1505.07657http://cds.cern.ch/record/2020526GMSB with Light Stops
http://cds.cern.ch/record/2020510
Gauge mediated supersymmetry breaking (GMSB) is an elegant mechanism to transmit supersymmetry breaking from the hidden to the MSSM observable sector, which solves the supersymmetric flavor problem. However the smallness of the generated stop mixing requires superheavy stops to reproduce the experimental value of the Higgs mass. Two possible ways out are: i) To extend GMSB by direct superpotential messenger-MSSM Yukawa couplings to generate sizeable mixing, thus reintroducing the flavor problem; ii) To extend the MSSM Higgs sector with singlets and/or triplets providing extra tree-level corrections to the Higgs mass. Singlets will not get any soft mass from GMSB and triplets will contribute to the $\rho$ parameter which could be an issue. In this paper we explore the second way by introducing extra supersymmetric triplets with hypercharges $Y=(0,\pm 1)$, with a tree-level custodial $SU(2)_L\otimes SU(2)_R$ global symmetry in the Higgs sector protecting the $\rho$ parameter: a supersymmetric generalization of the Georgi-Machacek model, dubbed as supersymmetric custodial triplet model (SCTM). The renormalization group running from the messenger to the electroweak scale mildly breaks the custodial symmetry. We will present realistic low-scale scenarios (with the NLSP being a Bino-like neutralino or the right-handed stau) based on general (non-minimal) gauge mediation and consistent with all present experimental data. Their main features are: i) Light ($\sim 1$ TeV) stops; ii) Exotic couplings ($H^\pm W^\mp Z$ and $H^{\pm\pm} W^\mp W^\mp$) absent in the MSSM and proportional to the triplets VEV, $v_\Delta$; and, iii) A possible (measurable) universality breaking of the Higgs couplings $\lambda_{WZ}=r_{WW}/r_{ZZ}\neq 1$.Delgado, AntonioGarcia-Pepin, MateoQuiros, MarianoSat, 30 May 2015 07:32:59 GMT27 May 2015arXiv:1505.07469http://cds.cern.ch/record/2020510Higgs portal valleys, stability and inflation
http://cds.cern.ch/record/2020444
If the top quark is heavy enough, the Standard Model potential is unstable at large Higgs values. This is particularly problematic during inflation, which sources large perturbations of the Higgs. The instability could be cured by a threshold effect induced by a scalar with a large vacuum expectation value and directly connected to the Standard Model through a Higgs portal coupling. However, we find that in a minimal model in which the scalar generates inflation, this mechanism does not stabilize the potential because the mass required for inflation is beyond the instability scale. On the other hand, if the potential is absolutely stable, successful inflation in agreement with current CMB data can occur along a valley of the potential with a Mexican hat profile. We revisit the stability conditions, independently of inflation, and clarify that the threshold effect cannot work if the Higgs portal coupling is too small. We also show that inflation in a false Higgs vacuum appearing radiatively for a tuned ratio of the Higgs and top masses leads to an amplitude of primordial gravitational waves that is far too high, ruling out this possibility.Ballesteros, GuillermoTamarit, CarlosSat, 30 May 2015 07:20:12 GMT27 May 2015arXiv:1505.07476http://cds.cern.ch/record/2020444The Fraternal WIMP Miracle
http://cds.cern.ch/record/2019461
We identify and analyze thermal dark matter candidates in the fraternal twin Higgs model and its generalizations. The relic abundance of fraternal twin dark matter is set by twin weak interactions, with a scale tightly tied to the weak scale of the Standard Model by naturalness considerations. As such, the dark matter candidates benefit from a "fraternal WIMP miracle," reproducing the observed dark matter abundance for dark matter masses between 10 and 100 GeV. However, the couplings dominantly responsible for dark matter annihilation do not lead to interactions with the visible sector. The direct detection rate is instead set via fermionic Higgs portal interactions, which are likewise constrained by naturalness considerations but parametrically weaker than those leading to dark matter annihilation. The predicted direct detection cross section is close to current LUX bounds and presents an opportunity for the next generation of direct detection experiments.Craig, NathanielKatz, AndreyThu, 28 May 2015 06:08:59 GMT26 May 2015arXiv:1505.07113http://cds.cern.ch/record/2019461Calculations of Inflaton Decays and Reheating: with Applications to No-Scale Inflation Models
http://cds.cern.ch/record/2019444
We discuss inflaton decays and reheating in no-scale Starobinsky-like models of inflation, calculating the effective equation-of-state parameter, $w$, during the epoch of inflaton decay, the reheating temperature, $T_{\rm reh}$, and the number of inflationary e-folds, $N_*$, comparing analytical approximations with numerical calculations. We then illustrate these results with applications to models based on no-scale supergravity and motivated by generic string compactifications, including scenarios where the inflaton is identified as an untwisted-sector matter field with direct Yukawa couplings to MSSM fields, and where the inflaton decays via gravitational-strength interactions. Finally, we use our results to discuss the constraints on these models imposed by present measurements of the scalar spectral index $n_s$ and the tensor-to-scalar perturbation ratio $r$, converting them into constraints on $N_*$, the inflaton decay rate and other parameters of specific no-scale inflationary models.Ellis, JohnGarcia, Marcos A GNanopoulos, Dimitri VOlive, Keith AThu, 28 May 2015 06:08:53 GMT26 May 2015arXiv:1505.06986http://cds.cern.ch/record/2019444Instanton Operators and the Higgs Branch at Infinite Coupling
http://cds.cern.ch/record/2018333
The richness of 5d $\mathcal{N}=1$ theories with a UV fixed point at infinite coupling is due to the existence of local disorder operators known as instanton operators. By considering the Higgs branch of $SU(2)$ gauge theories with $N_f \leq 7$ flavours at finite and infinite coupling, we write down the explicit chiral ring relations between instanton operators, the glueball superfield and mesons. Exciting phenomena appear at infinite coupling: the glueball superfield is no longer nilpotent and the classical chiral ring relations are quantum corrected by instanton operators bilinears. We also find expressions for the dressing of instanton operators of arbitrary charge. The same analysis is performed for $USp(2k)$ with an antisymmetric hypermultiplet and pure $SU(N)$ gauge theories.Cremonesi, StefanoFerlito, GiuliaHanany, AmihayMekareeya, NoppadolTue, 26 May 2015 05:52:39 GMT23 May 2015arXiv:1505.06302http://cds.cern.ch/record/2018333Precise determination of the Higgs mass in supersymmetric models with vectorlike tops and the impact on naturalness in minimal GMSB
http://cds.cern.ch/record/2018135
We present a precise analysis of the Higgs mass corrections stemming from vectorlike top partners in supersymmetric models. We reduce the theoretical uncertainty compared to previous studies in the following aspects: (i) including the one-loop threshold corrections to SM gauge and Yukawa couplings due to the presence of the new states to obtain the $\bar{\text{DR}}$ parameters entering all loop calculations, (ii) including the full momentum dependence at one-loop, and (iii) including all two-loop corrections but the ones involving $g_1$ and $g_2$. We find that the additional threshold corrections are very important and can give the largest effect on the Higgs mass. However, we identify also parameter regions where the new two-loop effects can be more important than the ones of the MSSM and change the Higgs mass prediction by up to 10 GeV. This is for instance the case in the low $\tan\beta$, small $M_A$ regime. We use these results to calculate the electroweak fine-tuning of an UV complete variant of this model. For this purpose, we add a complete $\textbf{10}$ and $\bar{\textbf{10}}$ representation of $SU(5)$ to the MSSM particle content. We embed this model in minimal Gauge Mediated Supersymmetry Breaking and calculate the electroweak fine-tuning with respect to all important parameters. It turns out that the limit on the gluino mass becomes more important for the fine-tuning than the Higgs mass measurements which is easily to satisfy in this setup.Nickel, KilianStaub, FlorianMon, 25 May 2015 05:25:39 GMT22 May 2015arXiv:1505.06077http://cds.cern.ch/record/2018135Consistent truncations of M-theory for general SU(2) structures
http://cds.cern.ch/record/2017974
In seven dimensions any spin manifold admits an SU(2) structure and therefore very general M-theory compactifications have the potential to allow for a reduction to N=4 gauged supergravity. We perform this general SU(2) reduction and give the relation of SU(2) torsion classes and fluxes to gaugings in the N=4 theory. We furthermore show explicitly that this reduction is a consistent truncation of the eleven-dimensional theory, in other words classical solutions of the reduced theory also solve the eleven-dimensional equations of motion. This reduction generalizes previous M-theory reductions on Tri-Sasakian manifolds and type IIA reductions on Calabi-Yau manifolds of vanishing Euler number. Moreover, it can also be applied to compactifications on certain G2 holonomy manifolds and to more general flux backgrounds.Triendl, HagenSat, 23 May 2015 05:53:15 GMT20 May 2015arXiv:1505.05526http://cds.cern.ch/record/2017974A comparison of updating algorithms for large N reduced models
http://cds.cern.ch/record/2017949
We investigate Monte Carlo updating algorithms for simulating $SU(N)$ Yang-Mills fields on a single-site lattice, such as for the Twisted Eguchi-Kawai model (TEK). We show that performing only over-relaxation (OR) updates of the gauge links is a valid simulation algorithm for the Fabricius and Haan formulation of this model, and that this decorrelates observables faster than using heat-bath updates. We consider two different methods of implementing the OR update: either updating the whole $SU(N)$ matrix at once, or iterating through $SU(2)$ subgroups of the $SU(N)$ matrix, we find the same critical exponent in both cases, and only a slight difference between the two.Pérez, Margarita GarcíaGonzález-Arroyo, AntonioKeegan, LiamOkawa, MasanoriRamos, AlbertoSat, 23 May 2015 05:52:41 GMT21 May 2015arXiv:1505.05784http://cds.cern.ch/record/2017949The cosmological Higgstory of the vacuum instability
http://cds.cern.ch/record/2017463
The Standard Model Higgs potential becomes unstable at large field values. After clarifying the issue of gauge dependence of the effective potential, we study the cosmological evolution of the Higgs field in presence of this instability throughout inflation, reheating and the present epoch. We conclude that anti-de Sitter patches in which the Higgs field lies at its true vacuum are lethal for our universe. From this result, we derive upper bounds on the Hubble constant during inflation, which depend on the reheating temperature and on the Higgs coupling to the scalar curvature or to the inflaton. Finally we study how a speculative link between Higgs meta-stability and consistence of quantum gravity leads to a sharp prediction for the Higgs and top masses, which is consistent with measured values.Espinosa, Jose RGiudice, Gian FMorgante, EnricoRiotto, AntonioSenatore, LeonardoStrumia, AlessandroTetradis, NikolaosThu, 21 May 2015 11:08:12 GMT18 May 2015arXiv:1505.04825http://cds.cern.ch/record/2017463LHC constraints on Gravitino Dark Matter
http://cds.cern.ch/record/2017095
Gravitino Dark Matter represents a compelling scenario in Supersymmetry, which brings together a variety of data from cosmology and collider physics. We discuss the constraints obtained from the LHC on supersymmetric models with gravitino dark matter and neutralino NLSP, which is the case most difficult to disentangle at colliders from a neutralino LSP forming DM. The phenomenological SUSY model with 19+1 free parameters is adopted. Results are obtained from broad scans of the phase space of these uncorrelated parameters. The relation between gravitino mass, gluino mass and reheating temperature as well as the derived constraints on these parameters are discussed in detail. This relation offers a unique opportunity to place stringent bounds on the cosmological model, within the gravitino dark matter scenario, from the results of the LHC searches in Run-2 and the planned High-Luminosity upgrade.Arvey, AlexandreBattaglia, MarcoCovi, LauraHasenkamp, JasperMahmoudi, FarvahTue, 19 May 2015 06:16:53 GMT18 May 2015arXiv:1505.04595http://cds.cern.ch/record/2017095Collider Interplay for Supersymmetry, Higgs and Dark Matter
http://cds.cern.ch/record/2017075
We discuss the potential impacts on the CMSSM of future LHC runs and possible electron-positron and higher-energy proton-proton colliders, considering searches for supersymmetry via MET events, precision electroweak physics, Higgs measurements and dark matter searches. We validate and present estimates of the physics reach for exclusion or discovery of supersymmetry via MET searches at the LHC, which should cover the low-mass regions of the CMSSM parameter space favoured in a recent global analysis. As we illustrate with a low-mass benchmark point, a discovery would make possible accurate LHC measurements of sparticle masses using the MT2 variable, which could be combined with cross-section and other measurements to constrain the gluino, squark and stop masses and hence the soft supersymmetry-breaking parameters m_0, m_{1/2} and A_0 of the CMSSM. Slepton measurements at CLIC would enable m_0 and m_{1/2} to be determined with high precision. If supersymmetry is indeed discovered in the low-mass region, precision electroweak and Higgs measurements with a future circular electron-positron collider (FCC-ee, also known as TLEP) combined with LHC measurements would provide tests of the CMSSM at the loop level. If supersymmetry is not discovered at the LHC, is likely to lie somewhere along a focus-point, stop coannihilation strip or direct-channel A/H resonance funnel. We discuss the prospects for discovering supersymmetry along these strips at a future circular proton-proton collider such as FCC-hh. Illustrative benchmark points on these strips indicate that also in this case FCC-ee could provide tests of the CMSSM at the loop level.Buchmueller, OCitron, MEllis, JGuha, SMarrouche, JOlive, K Ade Vries, KZheng, JiamingTue, 19 May 2015 06:13:24 GMT18 May 2015arXiv:1505.04702http://cds.cern.ch/record/2017075T-duality, Quotients and Currents for Non-Geometric Closed Strings
http://cds.cern.ch/record/2016741
We use the canonical description of T-duality as well as the formulation of T-duality in terms of chiral currents to investigate the geometric and non-geometric faces of closed string backgrounds originating from principal torus bundles with constant H-flux. Employing conformal field theory techniques, the non-commutative and non-associative structures among generalized coordinates in the so called Q-flux and R-flux backgrounds emerge by gauging the Abelian symmetries of an enlarged Rocek-Verlinde sigma-model and projecting the associated chiral currents of the enlarged theory to the T-dual coset models carrying non-geometric fluxes.Bakas, IoannisLust, DieterMon, 18 May 2015 05:25:27 GMT15 May 2015arXiv:1505.04004http://cds.cern.ch/record/2016741Soft Expansion of Double-Real-Virtual Corrections to Higgs Production at N$^3$LO
http://cds.cern.ch/record/2016733
We present methods to compute higher orders in the threshold expansion for the one-loop production of a Higgs boson in association with two partons at hadron colliders. This process contributes to the N$^3$LO Higgs production cross section beyond the soft-virtual approximation. We use reverse unitarity to expand the phase-space integrals in the small kinematic parameters and to reduce the coefficients of the expansion to a small set of master integrals. We describe two methods for the calculation of the master integrals. The first was introduced for the calculation of the soft triple-real radiation relevant to N$^3$LO Higgs production. The second uses a particular factorization of the three body phase-space measure and the knowledge of the scaling properties of the integral itself. Our result is presented as a Laurent expansion in the dimensional regulator, although some of the master integrals are computed to all orders in this parameter.Anastasiou, CharalamposDuhr, ClaudeDulat, FalkoFurlan, ElisabettaHerzog, FranzMistlberger, BernhardMon, 18 May 2015 05:25:14 GMT15 May 2015arXiv:1505.04110http://cds.cern.ch/record/2016733Dark Matter and Gauged Flavor Symmetries
http://cds.cern.ch/record/2016721
We investigate the phenomenology of flavored dark matter (DM). DM stability is guaranteed by an accidental ${\mathcal Z}_3$ symmetry, a subgroup of the standard model (SM) flavor group that is not broken by the SM Yukawa interactions. We consider an explicit realization where the quark part of the SM flavor group is fully gauged. If the dominant interactions between DM and visible sector are through flavor gauge bosons, as we show for Dirac fermion flavored DM, then the DM mass is bounded between roughly $0.5$ TeV and $5$ TeV if the DM multiplet mass is split only radiatively. In general, however, no such relation exists. We demonstrate this using scalar flavored DM where the main interaction with the SM is through the Higgs portal. For both cases we derive constraints from flavor, cosmology, direct and indirect DM detection, and collider searches.Bishara, FadyGreljo, AdmirKamenik, Jernej FStamou, EmmanuelZupan, JureMon, 18 May 2015 05:25:12 GMT14 May 2015arXiv:1505.03862http://cds.cern.ch/record/2016721Emergent Lorentz invariance with chiral fermions
http://cds.cern.ch/record/2016705
We study renormalization group flows in strongly interacting field theories with fermions that correspond to transitions between a theory without Lorentz invariance at high energies down to a theory with approximate Lorentz symmetry in the infrared. Holographic description of the strong coupling is used. The emphasis is made on emergence of chiral fermions in the low-energy theory.Kharuk, IvanSibiryakov, SergeyMon, 18 May 2015 05:24:24 GMT15 May 2015arXiv:1505.04130http://cds.cern.ch/record/2016705Beauty-quark and charm-quark pair production asymmetries at LHCb
http://cds.cern.ch/record/2015661
The LHCb collaboration has recently performed a first measurement of the angular production asymmetry in the distribution of beauty quarks and anti-quarks at a hadron collider. We calculate the corresponding standard model prediction for this asymmetry at fixed-order in perturbation theory. Our results show good agreement with the data, which is provided differentially for three bins in the invariant mass of the $b \bar b$ system. We also present similar predictions for both beauty-quark and charm-quark final states within the LHCb acceptance for a collision energy of $\sqrt{s} = 13 \, {\rm TeV}$. We finally point out that a measurement of the ratio of the $b \bar b$ and $c \bar c$ cross sections may be useful for experimentally validating charm-tagging efficiencies.Gauld, RhorryHaisch, UlrichPecjak, Ben DRe, EmanueleWed, 13 May 2015 06:14:36 GMT10 May 2015arXiv:1505.02429http://cds.cern.ch/record/2015661Dark Matter: Connecting LHC searches to direct detection
http://cds.cern.ch/record/2015659
In these proceedings we review the interplay between LHC searches for dark matter and direct detection experiments. For this purpose we consider two prime examples: the effective field theory (EFT) approach and the minimal supersymmetric standard model (MSSM). In the EFT scenario we show that for operators which do not enter directly direct detection at tree-level, but only via loop effects, LHC searches give complementary constraints. In the MSSM stop and Higgs exchange contribute to the direct detection amplitude. Therefore, LHC searches for supersymmetric particles and heavy Higgses place constraints on the same parameter space as direct detection.Crivellin, AndreasHoferichter, MartinProcura, MassimilianoTunstall, Lewis CWed, 13 May 2015 06:14:33 GMT09 May 2015arXiv:1505.02314http://cds.cern.ch/record/2015659Explaining the LHC flavour anomalies
http://cds.cern.ch/record/2014997
The LHC observed deviations from the Standard Model (SM) in the flavour sector: LHCb found a $4.3\,\sigma$ discrepancy compared to the SM in $b\to s\mu\mu$ transitions and CMS reported a non-zero measurement of $h\to\mu\tau$ with a significance of $2.4\,\sigma$. Here we discuss how these deviations from the SM can be explained, focusing on two models with gauged $L_\mu-L_\tau$ symmetry. The first model contains two scalar doublets and vector-like quarks while the second one employs three scalar doublets but does not require vector-like fermions. In both models, interesting correlations between $b\to s\mu\mu$ transitions, $h\to\mu\tau$, and $\tau\to3\mu$ arise.Crivellin, AndreasD'Ambrosio, GiancarloHeeck, JulianMon, 11 May 2015 05:20:41 GMT08 May 2015arXiv:1505.02026http://cds.cern.ch/record/2014997Same sign di-lepton candles of the composite gluons
http://cds.cern.ch/record/2014846
Composite Higgs models, where the Higgs boson is identified with the pseudo-Nambu-Goldstone-Boson (pNGB) of a strong sector, typically have light composite fermions (top partners) to account for a light Higgs. This type of models generically also predicts the existence of heavy vector fields (composite gluons) which appear as an octet of QCD. These composite gluons generically become very broad resonances once phase-space allows them to decay into two composite fermions. This makes their traditional experimental searches, which are designed to look for narrow resonances, quite ineffective. In this paper we, as an alternative, propose to utilize the impact of composite gluons on the production of top partners to constrain their parameter space. We place constraints on the parameters of the composite resonances using the 8 TeV LHC data and also assess the reach of the 14 TeV LHC. We find that the high luminosity LHC will be able to probe composite gluon masses up to $\sim 6$ TeV, even in the broad resonance regime.Azatov, AleksandrChowdhury, DebtoshGhosh, DiptimoyRay, Tirtha SankarSat, 09 May 2015 05:31:50 GMT06 May 2015arXiv:1505.01506http://cds.cern.ch/record/2014846$B$ Decays and Lepton Flavour (Universality) Violation
http://cds.cern.ch/record/2014838
LHCb found hints for physics beyond the standard model in $B\to K^*\mu^+\mu^-$, $B\to K^*\mu^+\mu^-/B\to K^*e^+e^-$ and $B_s\to\phi\mu^+\mu^-$. In addition, the BABAR results for $B\to D^{(*)}\tau\nu$ and the CMS excess in $h\to\tau^\pm\mu^\mp$ also point towards lepton flavour (universality) violating new physics. While $B\to D^{(*)}\tau\nu$ and $h\to\tau^\pm\mu^\mp$ can be naturally explained by an extended Higgs sector, the probably most promising explanation for the $b\to s\mu\mu$ anomalies is a $Z'$ boson. Furthermore, combining a 2HDM with a gauged $L_\mu-L_\tau$ symmetry allows for explaining the $b\to s\mu^+\mu^-$ anomalies and $h\to\tau^\pm\mu^\mp$ simultaneously, with interesting correlations to $\tau\to3\mu$. In the light of these deviations from the SM we also discuss the possibilities of observing lepton flavour violating $B$ decays (e.g. $B\to K^{(*)}\tau^\pm\mu^\mp$ and $B_s\to\tau^\pm\mu^\mp$) in $Z^\prime$ models.Crivellin, AndreasSat, 09 May 2015 05:30:34 GMT06 May 2015arXiv:1505.01527http://cds.cern.ch/record/2014838Features and New Physical Scales in Primordial Observables: Theory and Observation
http://cds.cern.ch/record/2014827
All cosmological observations to date are consistent with adiabatic, Gaussian and nearly scale invariant initial conditions. These findings provide strong evidence for a particular symmetry breaking pattern in the very early universe (with a close to vanishing order parameter, $\epsilon$), widely accepted as conforming to the predictions of the simplest realizations of the inflationary paradigm. However, given that our observations are only privy to perturbations, in inferring something about the background that gave rise to them, it should be clear that many different underlying constructions project onto the same set of cosmological observables. Features in the primordial correlation functions, if present, would offer a unique and discriminating window onto the parent theory in which the mechanism that generated the initial conditions is embedded. In certain contexts, simple linear response theory allows us to infer new characteristic scales from the presence of features that can break the aforementioned degeneracies among different background models, and in some cases can even offer a limited spectroscopy of the heavier degrees of freedom that couple to the inflaton. In this review, we offer a pedagogical survey of the diverse, theoretically well grounded mechanisms which can imprint features into primordial correlation functions in addition to reviewing the techniques one can employ to probe observations. These observations include cosmic microwave background anisotropies and spectral distortions as well as the matter two and three point functions as inferred from large-scale structure and potentially, 21 cm surveys.Chluba, JensHamann, JanPatil, Subodh PSat, 09 May 2015 05:29:11 GMT07 May 2015arXiv:1505.01834http://cds.cern.ch/record/2014827Assuming Regge trajectories in holographic QCD: from OPE to Chiral Perturbation Theory
http://cds.cern.ch/record/2014456
The soft wall model in holographic QCD has Regge trajectories but wrong operator product expansion (OPE) for the two-point vectorial QCD Green function. We modify the dilaton potential to comply OPE. We study also the axial two-point function using the same modified dilaton field and an additional scalar field to address chiral symmetry breaking. OPE is recovered adding a boundary term and low energy chiral parameters, $F_\pi$ and $L_{10}$, are well described analytically by the model in terms of Regge spacing and QCD condensates. The model nicely supports and extends previous theoretical analyses advocating Digamma function to study QCD two-point functions in different momentum regions.Cappiello, LuigiD'Ambrosio, GiancarloGreynat, DavidThu, 07 May 2015 06:00:11 GMT05 May 2015arXiv:1505.01000http://cds.cern.ch/record/2014456Golden Probe of the Top Yukuwa
http://cds.cern.ch/record/2014437
We perform a preliminary study of the ability of the Higgs decay to four leptons to shed light on the top quark Yukawa couplings. In particular we examine whether the $h\to 4\ell$ `golden channel' is sensitive to the $CP$ properties of the top quark couplings to the Higgs boson. We show that kinematic distributions are sensitive to interference of the next-to-leading order electroweak corrections with the tree level $ZZ$ contribution. This translates into a sensitivity to the top quark Yukawa couplings such that meaningful constraints on their $CP$ properties can begin to be obtained once $\sim 300$ fb$^{-1}$ of data has been collected at $\sim 14$ TeV, with significant improvements at higher luminosity or with a higher energy hadron collider. This makes the $h\to4\ell$ channel a useful probe of the top quark Yukawa couplings that is qualitatively different from already established searches in $h\to V\gamma$ two body decays, $tth$, and $gg\to h$. We also briefly discuss other potential possibilities for probing the top Yukawa $CP$ properties in $h\to2\ell\gamma$ and $\ell^+\ell^-\to h Z, h\gamma$.Chen, YiStolarski, DanielVega-Morales, RobertoThu, 07 May 2015 05:59:24 GMT05 May 2015arXiv:1505.01168http://cds.cern.ch/record/2014437Four-point correlation function of stress-energy tensors in N=4 superconformal theories
http://cds.cern.ch/record/2013066
We derive the explicit expression for the four-point correlation function of stress-energy tensors in four-dimensional N=4 superconformal theory. We show that it has a remarkably simple and suggestive form allowing us to predict a large class of four-point correlation functions involving the stress-energy tensor and other conserved currents. We then apply the obtained results on the correlation functions to computing the energy-energy correlations, which measure the flow of energy in the final states created from the vacuum by a source. We demonstrate that they are given by a universal function independent of the choice of the source. Our analysis relies only on N=4 superconformal symmetry and does not use the dynamics of the theory.Korchemsky, G PSokatchev, EThu, 30 Apr 2015 05:45:27 GMT29 Apr 2015arXiv:1504.07904http://cds.cern.ch/record/2013066