Search

The conventional ultralight QCD axion is typically rendered invisible at collider experiments by its large decay constant. What could also hint at its possible existence is the observation of other (heavy) particles that are characteristically related to the light axion. One such scenario is afforded within the framework of the clockwork mechanism where the axion can have suppressed couplings with the gluons or photons while its companion axion-like particles (ALPs) have relatively unsuppressed couplings. We study a minimal clockwork model for the QCD axion invoking a KSVZ-like setup and examine the visibility of the ALPs $(a_n)$ at the LHC through the process $p p \to a_n \, (+ \,{\rm additional \, jets})$, $a_n \to \gamma \gamma$. The model contains $N$ ALPs with a decay constant $f$ and masses defined by a scale $m$ characteristic of the nearest-neighbour interactions of the scalar fields. For $10\lesssim m \lesssim 100$ GeV, $f \sim 1$ TeV and $N \sim \mathcal{O}(10)$, the full spectrum of ALPs is accessible and the corresponding diphoton invariant mass distribution comprises a unique signature of a wide band of resonances. For the case of light ALPs $(m \sim \mathcal{O}(10 \,{\rm GeV}))$ with the axion being a dark matter candidate, the mass-splittings among the former are so small that the signal profile mimics that of a single broad resonance, or an $\textit{axion iceberg}$. The effect subsides for heavier ALPs, albeit still exhibiting undulating peaks. For light ALPs, the scenario is imminently testable by the end of LHC's Run 3 phase, with the estimated cumulative significance reaching the discovery threshold for an integrated luminosity of $\sim 300 {\rm \,fb^{-1}}$. While the signals for the heavier ALPs in this minimal setup may not be as prominent within the ongoing LHC operation, one could expect to probe a wider parameter space of the model at the forthcoming HL-LHC., Comment: 35 pages, 17 figures

Scenarios seeking to address the issue of electroweak symmetry breaking often have heavy colored gauge bosons coupling preferentially to the top quark. Considering the bulk Randall-Sundrum as a typical example, we consider the prospects of the first Kaluza-Klein mode ($G^{(1)}$) of the gluon being produced at the LHC in association with a $t \bar{t}$ pair. The enhanced coupling not only dictates that the dominant decay mode would be to a $t \bar{t}$ pair, but also to a very large $G^{(1)}$ width, necessitating the use of a renormalised $G^{(1)}$ propagator. This, alongwith the presence of large backgrounds (specially $t \bar{t} j j$), renders a conventional cut-based analysis ineffective, yielding only marginal significances of only around 2$\sigma$. The use of Machine Learning (ML) techniques alleviates this problem to a great extent. In particular, the use of Artificial Neural Networks helps us identify the most discriminating observables, thereby allowing a significance in excess of 4$\sigma$ for $G^{(1)}$ masses of $\sim$ 4 TeV., Comment: 35 pages, 9 figures, 5 tables

The simplest cosmological model ($\Lambda$CDM) is well-known to suffer from the Hubble tension, namely an almost $5 \sigma$ discrepancy between the (model-based) early-time determination of the Hubble constant $H_0$ and its late-time (and model-independent) determination. To circumvent this, we introduce an additional energy source that varies with the redshift as $(1 + z)^n$, where $0 < n < 3$, and test it against the Pantheon Compilation of Type Ia Supernovae as well as the CMBR observations (at $z \approx 1100$). The deduced $H_0$ is now well-consistent with the value obtained from local observations of Cepheid variables. Suggesting a non-zero value for the curvature density parameter, positive (negative) for $n > 2$ ($n < 2$), the resolution is also consistent with the BAO data., Comment: 6 pages, 4 figures, 1 table

We calculate QED corrections to the semileptonic decays $H_1 \to H_2\ell^+\ell^-$ where $\ell=e, \mu$ and $H_{1,2}$ are hadrons. The soft and/or collinear divergences are regulated in a gauge-invariant manner and demonstrably cancel, leaving behind a finite residue that depends on the (infrared) momentum cutoff below which a photon is considered to be indistinguishable. On resuming, the said sensitivity reduces drastically, $\mathcal{i}$.$\mathcal{e}$., for the NLL result as compared to the NLO one. The overall correction is negative and its magnitude is larger for a lighter lepton. For $B \to K^{(*)}$ decays, the corrections improve the agreement for the differential distributions, while the behavior is more complicated for $\Lambda_b \to \Lambda^{(*)}$ decays. Rather intriguingly, the corrections serve to regenerate the tension for the lepton flavor universality observables $R_K$ and $R_{K^*}$., Comment: 27 pages, 9 figures

Cosmological models with inflation and those with bounce have their own strengths and weaknesses. Here we construct a model in which a phase of bounce is followed by a viable inflationary phase. This incorporates several advantages of both and hence, is a more viable model for cosmic evolution. We explore scenarios wherein the bouncing phase smoothly transits to an inflationary one, with the pivot scale leaving the Hubble horizon during the latter era, thereby maintaining consistency with observations. Staying within the ambit of Einstein-Hilbert gravity augmented by the inflaton, we ensure a pre-inflationary bounce by introducing a second scalar field that helps engineer the requisite violation of the null energy condition. Potential ghost instabilities can be mitigated by invoking a non-trivial coupling between the two scalar fields., Comment: 34 pages, 7 figures, Published in Int.J.Mod.Phys.D

We develop a new class of clockwork theories with an augmented structure of the near-neighbour interactions along a one-dimensional closed chain. Such a topology leads to new and attractive features in addition to generating light states with hierarchical couplings via the usual clockwork mechanism. For one, there emerges a $\mathbb{Z}_2$ symmetry under the exchange of fields resulting in a physical spectrum consisting of states, respectively even and odd under the exchange parity with a two-fold degeneracy at each level. The lightest odd particle, being absolutely stable, could be envisaged as a potential dark matter candidate. The theory can also be obtained as a deconstruction of a five-dimensional theory embedded in a geometry generated by a linear dilaton theory on a $S^1/\mathbb{Z}_2$ orbifold with three equidistant 3-branes. Analogous to the discrete picture, the $\mathbb{Z}_2$ symmetry in the bulk theory necessitates the existence of a KK spectrum of even and odd states, with doubly degenerate modes at each KK level when subject to certain boundary conditions., Comment: 37 pages, 4 figures. Typos corrected and a new section added. Version to appear in JHEP

The continued non-observation of events emanating from dark matter (DM) annihilations in various direct and indirect detection experiments calls into question the mechanism for determining the relic density of a weakly interacting massive particle. However, if the relic density is determined primarily by a semi-annihilation process, as opposed to the usual annihilation, this tension can be ameliorated. Here, we investigate a Z3 symmetric effective field theory incorporating a fermionic dark matter that semi-annihilates to right-handed neutrinos (RHN). The dynamics of the RHN and the impact of its late decays are also scrutinised while obtaining the correct DM relic. Finally, indirect detection bounds on the semi-annihilation cross-sections are drawn from the gamma-ray observations in the direction of Dwarf Spheroidal Galaxies (Fermi-LAT), and including the projections obtained for the H.E.S.S. and the CTA detectors., Comment: 22 pages, 7 figures

Considering a six-dimensional geometry orbifolded on $S^1/Z_2\times S^1/Z_2$ with quarks and leptons localised on orthogonal branes, we show that the construction admits observable $n-\bar{n}$ oscillation while naturally suppressing the proton decay rates. Consistent with other low-energy observables, the model also accommodates baryogenesis at $\mathcal{O}$(10 TeV) scale., Comment: 6 pages, 1 figure

We reassess non-standard triple gauge couplings in the light of the recent $(g-2)_\mu$ measurement at FNAL, the new lattice theory result of $(g-2)_\mu$ and the updated measurements of several $B$-decay modes. In the framework of SMEFT, three bosonic dimension-6 operators are invoked to parametrize physics beyond the Standard Model and their contributions to such low-energy observables computed. Constraints on the corresponding Wilson coefficients are then derived from fits to the current experimental bounds on the observables and compared with the most stringent ones available from the 13 TeV LHC data in the $W^+ W^-$ and $W^\pm Z$ production channels., Comment: 13 pages. Typos corrected, figures updated and a few segments expanded. Minor change in the results. Version to appear in PRD

Exotic leptons in large gauge multiplets, appearing in many scenarios beyond the Standard Model (SM), can be produced at the LHC in pairs or association. Owing to their large masses, their eventual decay products -- SM leptons and bosons -- tend to be highly boosted, with the jets stemming from the SM bosons more likely to manifest themselves as a single fat-jet rather than two resolved ones. With the corresponding SM backgrounds being suppressed, final states with two or three leptons and one or two fat-jets are expected to be sensitive in probing exotic fermions much heavier than 1 TeV, and we propose and investigate an appropriate search strategy. To concentrate on the essential, we consider extensions of the SM by leptonic multiplets of a single kind (triplets, quadruplets or quintuplets), bearing in mind that such simplified models typically arise as low-energy limits of more ambitious scenarios addressing various lacunae of the SM. Performing a systematic and comprehensive study of nine such scenarios at the 13 TeV LHC, we find that the corresponding $5\sigma$ discovery reaches a range from 985 GeV to 1650 GeV (1345 GeV to 2020 GeV) for 300 (3000) fb$^{-1}$., Comment: 26 pages, 9 figures, 10 tables

Vectorlike quarks have been shown to resolve certain long-standing discrepancies pertaining to the bottom sector. We investigate, here, the prospects of identifying the existence of a topless vectorlike doublet $(B,~Y)$, as is preferred by the electroweak precision measurements. Concentrating on single production, $viz.$ $B \bar b$ with $B \to b + Z/H$ subsequently, we find that the fully hadronic decay-channel is susceptible to discovery provided jet substructure observables are used. At the 13 TeV LHC with an integrated luminosity of 300 fb$^{-1}$, a modest value of the chromomagnetic transition moments allows for the exclusion of $M \lesssim 1.8(2.2)$ TeV in the $Z$ and $H$ channels respectively.

The very large (100-1000) mass-to-light ratio applicable to the ultra-faint dwarf galaxies (UFDs) implies a high concentration of dark matter, thus rendering them ideal theatres for indirect signatures of dark matter. In this paper, we consider 14 recently discovered UFDs and study the electromagnetic radiation emanating from them over a wide range, from gamma ray down to radio frequencies. We analyze the Fermi-LAT data on high energy gamma rays and radio fluxes at the GMRT and VLA to obtain upper limits on annihilation cross section $\langle\sigma v\rangle$ in a model independent way. We further discuss the sensitivity of the Square Kilometer Array radio telescope in probing the synchrotron radiation from the aforementioned UFDs. We also investigate the dependences of the said upper limits on the uncertainties in the determination of various astrophysical parameters., Comment: 47 pages, 14 figures, Same as published version

A very economic scenario with just three extra scalar fields beyond the Standard Model is invoked to explain the muon anomalous magnetic moment, the requisite relic abundance of dark matter as well as the Xenon-1T excess through the inelastic down-scattering of the dark scalar., Comment: 7 pages, 4 figures; matches published version

We consider an anomaly-free $\mathrm{U}(1)$ extension of the Standard Model with three right-handed neutrinos (RHNs) and two complex scalars, wherein the charge assignments preclude all tree-level mass terms for the neutrinos. Considering this setup, in turn, to be only a low-energy effective theory, we introduce higher-dimensional terms {\em a la} Froggatt-Nielsen to naturally generate tiny neutrino masses. One of the RHNs turns out to be very light, thereby constituting the main decay mode for the $Z'$ and hence relaxing the LHC dilepton resonance search constraints. This very RHN has a lifetime comparable to or bigger than the age of the Universe, and, hence, could account for a non-negligible fraction of the dark matter.

Dark matter particles with masses in the sub-GeV range have escaped severe constraints from direct detection experiments such as LUX, PANDAX-II and XENON100 as the corresponding recoil energies are, largely, lower than the detector thresholds. In a companion paper, we demonstrated, in a model independent approach, that a significantly large fraction of the parameter space escapes the cosmological and astrophysical constraints. We show here, though, that the remaining parameter space lends itself to the possibility of discovery at both direct detection experiments (such as CRESST-II) as well as in a low-energy collider such as Belle-II., Comment: 33 pages, 8 figures

Extant anomalies in several semileptonic $B$-meson decays argue for physics beyond the Standard Model. Measurements of both neutral-current decays (such as $R_K$, $R_{K^*}$ and $B_s\rightarrow \phi\mu\mu$) as well as charged-current ones- $R(D)$ and $R(D^*)$ -provide strong hints for the violation of lepton flavor universality. Recent studies have shown that a class of effective field theory (EFT) models may explain such anomalies in terms of only a few parameters which can be determined phenomenologically. In this literature, we examine such resolutions in the context of the requisite $(\bar{s}$ $b$)($\bar\tau\ \tau)$ operator, and look for its signals at the 13 TeV LHC, with a final state of one $b$-jet, and an oppositely charged $\mu$-$\tau$ pair, with the muon coming from the decay of one of the $\tau$ leptons. We obtain discovery and exclusion limits on the model parameters as a function of luminosity at the 13 TeV LHC., Comment: 19 pages, 19 figures, References added, Figures are changed

Recent results from several direct detection experiments have imposed severe constraints on the multi-GeV mass window for various dark matter (DM) models. However, many of these experiments are not sensitive to MeV scale DM as the corresponding recoil energies are, largely, lower than the detector thresholds. We reexamine the light scalar DM in a model-independent approach. In this first of a two-part work, we develop an appropriate methodology to determine the effective coupling of such a DM to hadrons, thereby allowing for the determination of the corresponding annihilation rates. We find that while the parameter space can be constrained using cosmological and astrophysical observations, a significantly large fraction is still viable. In the companion paper, we study the sensitivity of both direct detection experiments as well as colliders to such a DM., Comment: 35 pages, 8 figures. arXiv admin note: substantial text overlap with arXiv:1711.03691

Models incorporating moderately heavy dark matter (DM) typically need charged (scalar) fields to establish admissible relic densities. Since the DM freezes out at an early epoch, thermal corrections to the cross sections can be important. In a companion paper [arXiv:1812.04247v2] we established that the infrared (IR) divergences accruing from scalar-photon interactions cancel to all orders in perturbation theory. The corresponding infrared finiteness of thermal fermionic QED has already been established. Here, we study the IR behaviour at finite temperatures, of a theory of dark matter interacting with charged scalars and fermions, which potentially contains both both linear and sub-leading logarithmic divergences. We prove that the theory is IR-finite to all orders with the divergences cancelling when both absorption and emission of photons from and into the heat bath are taken into account. While 4-point interaction terms are known to be IR finite, their inclusion leads to a neat exponentiation. The calculation follows closely the technique used for the scalar finite temperature theory., Comment: 31 pages, 4 figures; original set of two papers on (1) T=0 and (2) finite T scalar and bino-like theories of dark matter revised into (1) scalar electrodynamics at all temperatures and (2) bino-like theory of dark matter at all temperatures. This is paper 2

Models explaining dark matter typically include interactions with charged scalar and fermion fields. The Infra-Red (IR) finiteness of thermal field theories of charged fermions (fermionic QED) has been proven to all orders in perturbation theory. Here we reexamine the IR behaviour of charged scalar theories at finite temperature. Using the method of Grammer and Yennie, we identify and factorise the infra-red divergences to all orders in perturbation theory. The inclusion of IR finite pieces arising from the 4-point interaction terms of scalars with photon fields is key to the exponentiation. We use this in a companion paper to prove the IR finiteness of the corresponding thermal theory which is of relevance in dark matter calculations., Comment: 41 pages, 11 figures; original set of two papers on (1) T=0 and (2) finite T scalar and bino-like theories of dark matter revised into (1) scalar electrodynamics at all temperatures and (2) bino-like theory of dark matter at all temperatures. This is paper 1. arXiv admin note: substantial text overlap with arXiv:1812.06468

The minimal Universal Extra Dimension scenario is highly constrained owing to opposing constraints from the observed relic density on the one hand, and the non-observation of new states at the LHC on the other. Simple extensions in five-dimensions can only postpone the inevitable. Here, we propose a six-dimensional alternative with the key feature being that the SM quarks and leptons are localized on orthogonal directions whereas gauge bosons traverse the entire bulk. Several different realizations of electroweak symmetry breaking are possible, while maintaining agreement with low energy observables. This model is not only consistent with all the current constraints opposing the minimal Universal Extra Dimension scenario but also allows for a multi-TeV dark matter particle without the need for any fine-tuning. In addition, it promises a plethora of new signatures at the LHC and other future experiments., Comment: 43 pages, 5 figures, accepted for publication in JHEP

Searching for non-standard neutrino interactions, as a means for discovering physics beyond the Standard Model, has one of the key goals of dedicated neutrino experiments, current and future. We demonstrate here that much of the parameter space accessible to such experiments is already ruled out by the RUN II data of the Large Hadron Collider experiment., Comment: 5 pages, 2 figures

In a recent paper arXiv:1706.08437, we have advanced a minimal resolution of some of the persistent anomalies in semileptonic $B$-decays. These include the neutral-current observables $R_K$ and $R_{K^*}$, as well as the charged-current observables $R(D)$ and $R(D^*)$. Recently, it has been observed that the semileptonic decays of the $B_c$ meson also hint at a similar type of anomaly. In this longer version, we discuss in detail why, if the anomalies are indeed there, it is a challenging task to explain the data consistently in terms of a simple and compelling new physics scenario. We find that the minimal scheme to achieve a reasonable fit involves the inclusion of just two (or, at worst, three with a possible symmetry relationship between their Wilson coefficients) new current-current operators, constructed in terms of the flavour eigenstates, augmented by a change of basis for the charged lepton fields. With only three unknown parameters, this class of models not only explain all the anomalies (including that in $B_c \to J/\psi \, \ell \nu$) to a satisfactory level but also predict some interesting signatures, like $B\to K\mu\tau$, $B_s\to \tau\tau$, or $B\to K$ plus missing energy, that can be observed at LHCb or Belle-II., Comment: Version accepted in Nuclear Physics B

Recent results from direct detection experiments such as LUX, PANDAX-II and XENON100 have imposed severe constraints on the multi-GeV mass window in various dark matter (DM) models. However, many of these experiments are not sensitive to MeV scale DM as the corresponding recoil energies are, largely, lower than the detector thresholds. Re-examining the light scalar DM in a model-independent approach, we find that while the parameter space can be constrained using cosmological and astrophysical observations, a significantly large fraction is still viable. We further demonstrate that the remaining parameter space lends itself to the possibility of discovery at both direct detection experiments (such as CRESST-II) as well as in a low-energy collider such as Belle-II., Comment: supplanted by arXiv:1903.06049 and another paper in series

It is a challenging task to explain, in terms of a simple and compelling new physics scenario, the intriguing discrepancies between the standard model expectations and the data for the neutral-current observables $R_K$ and $R_{K^*}$, as well as the charged-current observables $R(D)$ and $R(D^*)$. We show that this can be achieved in an effective theory with only two unknown parameters. In addition, this class of models predicts some interesting signatures in the context of both $B$ decays as well as high-energy collisions., Comment: Matches with the published version

The Universal Extra Dimension (UED) paradigm is particularly attractive as it not only includes a natural candidate for the Dark Matter particle but also addresses several issues related to particle physics. Non-observations at the Large Hadron Collider, though, has brought the paradigm into severe tension. However, a particular 5-dimensional UED model emerges from a six-dimensional space-time with nested warping. The $AdS_6$ bulk protects both the Higgs mass as well as the UED scale without invoking unnatural parameter values. The graviton excitations in the sixth direction open up new (co-)annihilation channels for the Dark Matter particle, thereby allowing for phenomenological consistency, otherwise denied to the minimal UED scenario. The model leads to unique signatures in both satellite-based experiments as well as the LHC., Comment: 16 pages, 4 figures, To be published in JCAP

Taking advantage of the fact that the flavor of the neutrino in semileptonic $B$ decays $B\to D^{(*)}\tau\nu$ is not known, we show how a minimal set of higher-dimensional lepton flavor violating (LFV) operators can explain the $R(D^{(*)})$ anomalies, and as a spin-off, can give rise to the LFV decay of the Higgs boson, $h\to\mu\tau$. We also show how none but the minimal set of operators survive the present data., Comment: 15 pages, 4 figures. v2: A few references added. Version to be published in Phys Rev D

We consider a scenario of Minimal Supersymmetric Standard Model (MSSM) with $R$-parity violation, where the lightest supersymmetric particle (LSP) is the lighter sbottom $(\tilde b_1)$. We study the production of a sbottom pair at the LHC and their subsequent decays through the baryon number violating $(U D D)$ operators leading to a top pair with two light quarks. Looking for both semi-leptonic and fully hadronic (no leptons) final states, we perform cut-based as well as multivariate analyses (MVA) to estimate the signal significance at the 13 TeV run of the LHC. We find that a cut-based analysis can probe sbottom mass upto $\sim 650 $ GeV which may be extended upto $\sim 750 $ GeV using MVA with $300~{\rm fb}^{-1}$ integrated luminosity. The fully hadronic final state, however, is not as promising., Comment: 19 pages, 9 figures, 8 tables, revised leptonic analysis, new figures added, notable improvement in LHC sensitivity

We discuss the collider bounds on minimal Universal Extra Dimension (mUED) model from LHC Run-I and II data. The phenomenology of mUED is determined by only two parameters namely, the compactification scale ($R^{-1}$) of the extra dimension and cutoff scale ($\Lambda$) of the theory. The characteristic feature of mUED is the occurrence of nearly degenerate mass spectrum for the Kaluza-Klein (KK) particles and hence, soft leptons, soft jets at the collider experiments. The degree of degeneracy of KK-mass spectrum crucially depends on $\Lambda$. The strongest direct bound on $R^{-1}$ ($\sim $950 GeV for large $\Lambda$) arises from a search for a pair of soft dimuons at the Large Hadron Collider (LHC) experiment with 8 TeV center-of-mass energy and $20~{\rm fb}^{-1}$ integrated luminosity. However, for small $\Lambda$ and hence, small splitting within the first KK-level, the bounds from the dimuon channel is rather weak. On the other hand, the discovery of 126 GeV Higgs boson demands small $\Lambda$ to prevent the scalar potential form being unbounded from below. We discuss LHC monojet searches as a probe of low $\Lambda$ region of mUED parameter space. We also compute bounds on the mUED parameter space from 13 TeV multijets results., Comment: 6 pages, 3 figures

The absence, so far, of any graviton signatures at the LHC imposes severe constraints on the Randall-Sundrum scenario. Although a generalization to higher dimensions with nested warpings has been shown to avoid these constraints, apart from incorporating several other phenomenologically interesting features, moduli stabilization in such models has been an open question. We demonstrate here how both the moduli involved can be stabilized, employing slightly different mechanisms for the two branches of the theory. This also offers a dynamical mechanism to generate and stabilize the scale for the Universal Extra Dimensions, another long-standing issue., Comment: 22 pages, 3 figures

We examine the observed diphoton excess at 750 GeV in the framework of constrained Minimal Supersymmetric Standard Model (cMSSM). The consistency of cMSSM with the discovery of a 125 GeV Higgs boson and PLANCK/WMAP data for dark matter relic density (RD) demands large mixing in the scalar top (stop) sector and consequently, the existence of a light stop quasi-degenerate with the lightest neutralino. Small decay width due to kinematic and loop suppression of such a stop allows for the existence of stop-antistop bound states (stoponia). Identifying the particular part of cMSSM parameter space consistent with Higgs boson mass as well as RD, we study stoponia as the source of the diphoton excess., Comment: References added

At the LHC, the Littlest Higgs Model with $T$-parity is characterised by various production channels. If the $T$-odd quarks are heavier than the exotic partners of the $W$ and the $Z$, then associated production can be as important as the pair-production of the former. Studying both, we look for final states comprising at least one lepton, jets and missing transverse energy. We consider all the SM processes that could conspire to contribute as background to our signals, and perform a full detector level simulation of the signal and background to estimate the discovery potential at the current run as well as at the scheduled upgrade of the LHC. We also show that, for one of the channels, the reconstruction of two tagged $b$-jets at the Higgs mass $(M_h = 125~{\rm GeV})$ provides us with an unambiguous hint for this model., Comment: 22 pages, 3 captioned figures, 8 Tables; minor modifications, version published in JHEP

Generalizing the Randall-Sundrum scenario to higher dimensions with nested warpings has been shown to avoid the constraints besetting the former. In the first paper of this series [JHEP 1509 (2015) 202], the Standard Model gauge and fermion fields were extended into such a six-dimensional bulk and the construction was shown to have several interesting and welcome features. In this paper, we discuss the electroweak symmetry breaking, presenting a novel Higgs localization mechanism that leads to interesting phenomenology in the Higgs sector. Localizing the Higgs modifies the $Z_{\mu}$ and $W_{\mu}$ boson wavefunctions, which leads to tree level changes in the oblique parameters. Using these as well as the correction to low-energy four-Fermi operators, we derive the constraints on our model and also discuss the gauge coupling evolution therein. Amusingly, the model can naturally incorporate a Higgs resonance in the 700--800 GeV range., Comment: 36 pages , 5 figures

The lack of evidence for a TeV-mass graviton has been construed as constricting the Randall-Sundrum model. However, a doubly-warped generalization naturally avoids such restrictions. We develop, here, the formalism for extension of the Standard Model gauge bosons and fermions into such a six-dimensional bulk. Apart from ameliorating the usual problems such as flavour-changing neutral currents, this model admits two very distinct phases, with their own unique phenomenologies., Comment: 44 pages, 5 figures, version to appear in JHEP. Corrected minor typographical errors

Modulus stabilization, a must for explaining the hierarchy problem in the context of the Randall-Sundrum (RS) scenario, is traditionally achieved through the introduction of an extra field with {\em ad hoc} couplings. We point out that the stabilization can, instead, be achieved in a purely geometrodynamical way, with plausible quantum corrections in the gravity sector playing the key role. The size of the corrections that lead to acceptable phenomenology is also delineated.

The negative results in the search for Kaluza-Klein graviton modes at the LHC, when confronted with the discovery of the Higgs, has been construed to have severely limited the efficacy of the Randall-Sundrum model as an explanation of the hierarchy problem. We show, though, that the presence of multiple warping offers a natural resolution of this conundrum through modifications in both the graviton spectrum and their couplings to the Standard Model fields., Comment: 16 pages, 6 figures

We study the effects of non-standard interactions on the oscillation pattern of atmospheric neutrinos. We use neutrino oscillograms as our main tool to infer the role of non-standard interactions (NSI) parameters at the probability level in the energy range, $E \in [1,20]$ GeV and zenith angle range, $\cos \theta \in [-1,0]$. We compute the event rates for atmospheric neutrino events in presence of NSI parameters in the energy range $E \in [1,10]$ GeV for two different detector configurations - a magnetized iron calorimeter and an unmagnetized liquid Argon time projection chamber which have different sensitivities to NSI parameters due to their complementary characteristics. As an application, we discuss how NSI parameter, $\epsilon_{\mu\tau}$ impacts the determination of the correct octant of $\theta_{23}$., Comment: v2: matches published version in Phys. Rev. D

There are two Z-peak observables related to the pair production of bottom quarks that show a deviation of about 2.5\sigma\ each from Standard Model expectations. While the discrepancy in the forward-backward asymmetry is a long-standing one, the tension for the second observable, namely the ratio of the partial width for a Z decaying to a pair of bottom quarks to the total hadronic decay width of the Z, has recently gone up due to a full two-loop evaluation of the Standard Model contributions. We show how both these discrepancies may be explained in the framework of new physics that couples only to the third generation of quarks. In the paradigm of effective operators, the Wilson coefficients of some of the possible operators are already very tightly constrained by flavour physics data. However, there still remain certain operators, particularly those involving right-chiral quark fields, which can successfully explain the anomalies. We also show how the footprints of such operators may be observed at the upgraded LHC., Comment: v2: A few clarifications, results unchanged. Published version

A Gauss-Bonnet term naturally appears in the action for gravity when one considers the existence of space time with dimensions more than 1+3. A variety of inflationary models can be obtained within such a framework, once the scale factor for the hidden dimension(s) is not constrained to be the same as that of the visible ones. In particular, the need for an adhoc inflaton field is eliminated. The phase space has a rich structure with different types of solutions, both stable and unstable. For a large class of solutions, the scale factors rapidly approach an asymptotic exponential form. Furthermore, sufficient inflation can be obtained for only a modest compression of the hidden world, if the latter is of a sufficiently large dimension., Comment: 11 pages, 7 figures

Present and future expected limits on interactions between dark matter and various quarks are thoroughly investigated in a model-independent way. In particular, the constraints on the interactions from the Large Hadron Collider (LHC) experiment are carefully considered with focusing on mono jet + missing transverse energy, mono b-jet + missing transverse energy, and top quark(s) + missing transverse energy channels. Model-independent upper limits (expected limits) on the cross section times acceptance for non-standard model events are derived at 7 TeV (8 or 14 TeV) running of the LHC experiment. With assuming that the dark matter is a singlet real scalar or a singlet Majorana fermion, we also put constraints on several operators describing its interactions with up, down, strange, charm, bottom and top quarks. These constraints are compared to those obtained by cosmological and astrophysical observations of the dark matter., Comment: 21 pages, 4 figures, v2:some comments are added

The initial data on the production and decay of the Higgs boson reported significant deviations from the Standard Model (SM) expectations, prompting much speculation about its couplings to the other particles. Although the latest data has veered towards conformity with the SM, there is yet room for a sizable deviation from the SM values of the coupling of the Higgs boson with $t\bar{t}$, and to a smaller extent, of that with $W^+W^-$ and $ZZ$. Keeping the fluid nature of the data in mind, this opens up an interesting avenue to explore regarding unitarity of gauge boson scattering and the stability of the electroweak vacuum in the presence of anomalous couplings. We show that, for some typical benchmark points, unitarity in gauge boson scattering breaks down between 1 and 10 TeV. We also show that if there are no new light degrees of freedom, the Higgs quartic coupling becomes negative at around the same point, making the electroweak vacuum unstable. Thus, some new ultraviolet completing new physics is demanded at that scale to cancel both these anomalous behaviours if such deviations from the SM couplings are indeed established., Comment: 15 pages, 6 figures. Discussion on recent results of ATLAS and CMS. Conclusions unchanged. Author list modified. Version accepted in Physical Review D

We investigate how far a new physics scenario affecting primarily the third generation fermions can ameliorate the tension between B-decay observables and Standard Model expectations. Adopting a model-independent approach, we find that among the three observables that show signs of such a tension, viz. the branching fractions for $B^+\to\tau\nu$, $B_d\to D(D^\ast)\tau\nu$, and the like-sign dimuon anomaly in neutral B decays, the first two can be explained adequately, while there is only a marginal improvement for the third. As a spin-off, it is shown that one can also accommodate a change in the branching fraction of the Higgs boson to a $\tau$ lepton pair from the SM expectation, if such a change is established in future data., Comment: Almost identical with version 2, version published in Phys. Rev. D

The signal strength of the recently discovered Higgs boson-like particle in the diphoton channel seemingly constrains physics beyond the standard model to a severe degree. However, the reported signal strength is prone to possible underestimation of uncertainties. We propose a discriminant that is relatively free of many of the theoretical uncertainties, and use this to gauge the impact on the phenomenological MSSM. A Bayesian global fit to all the pre-LHC data results in posterior distributions for the masses that are neither very restrictive, nor sufficiently prior-independent (except for the Higgs and stop masses). The imposition of the Higgs data, on the other hand, yields interesting and nearly prior-independent constraints. In particular, the existence of some light superpartners is favoured., Comment: v2: added references and minor changes, published version

The Littest Higgs model with T-parity (LHT), apart from offering a viable solution to the naturalness problem of the Standard Model, also predicts a set of new fermions as well as a candidate for dark matter. We explore the possibility of discovering the heavy T-odd quark Q_H at the LHC in a final state comprising two hard jets with a large missing transverse momentum. Also discussed is the role of heavy flavor tagging., Comment: Changes in text. Some references added

The LHC may be currently seeing the first hints of the Higgs boson. The dominant production mode for the Higgs at the LHC involves a top-quark loop. An accurate measurement of Higgs production cross-sections and decay widths can thus be used to obtain limits on anomalous top couplings. We find that such an exercise could potentially yield constraints that are stronger than those derived from low-energy observables as well as direct bounds expected from the top pair-production process., Comment: Version published in JHEP

The search for heavy resonances in the dijet channel is part of the on-going physics programme, both at the Tevatron and at the LHC. Lower limits have been placed on the masses of dijet resonances predicted in a wide variety of models. However, across experiments, the search strategy assumes that the effect of the new particles is well-approximated by on-shell production and subsequent decay into a pair of jets. We examine the impact of off-shell effects on such searches, particularly for strongly interacting resonances., Comment: Version published in JHEP

We discuss the signatures, at the LHC, of the (1,0)-th Kaluza-Klein (KK) gluon and quarks in the framework of the two universal extra dimensional (2UED) model. Once produced, these particles typically suffer a cascade of decays terminating in the Dark Matter candidate apart from Standard Model particles. In this article, we are interested in focus on a particular signature of 2UED wherein the final state comprises of at least four jets in association with a hard photon and missing transverse energy. Several kinematic cuts are devised to enhance the signal to background ratio. Finally, as a road map to parameter determination at the LHC, we point out an interesting correlation between the peak position of the M_eff distributions with the compactification radius R and the cut-off scale M_s., Comment: 29 pages, 11 postscript figures, one typo corrected

The introduction of a delay in the Friedmann equation of cosmological evolution is shown to result in the very early universe undergoing the necessary accelerated expansion in the usual radiation (or matter) dominated phase. Occurring even without a violation of the strong energy condition, this expansion slows down naturally to go over to the decelerated phase, namely the standard Hubble expansion. This may obviate the need for a scalar field driven inflationary epoch., Comment: 12 pages, 3 figures, Revised with more elaborate discussions. Accepted for publication in JCAP

The scalar partner of the top quark (the stop) is relatively light in many models of supersymmetry breaking. We study the production of stops at the Large Hadron Collider (LHC) and their subsequent decays through baryon-number violating couplings such that the final state contains no leptons. A detailed analysis performed using detector level observables demonstrate that stop masses upto $\sim 600 \gev$ may be explored at the LHC depending on the branching ratios for such decays and the integrated luminosity available. Extended to other analogous scenarios, the analysis will, generically, probe even larger masses., Comment: 11 pages, 6 figs

We study signatures of R-parity violation in the production of supersymmetric particles at the LHC, and the subsequent decay of the lightest neutralino being the end product of a supersymmetric cascade decay. In doing so, we pay particular attention to the possible flavour structure of the operators, and how one may discriminate between different possibilities. A neutralino LSP would couple to all quarks and leptons and a comparative study of its decays provides an optimal channel for the simultaneous study of all 45 R-violating operators. By studying the expected signals from all these operators, we demonstrate the ability to understand whether more than one coupling dominates, and to map the experimental signatures to operator hierarchies that can then be compared against theoretical models of flavour. Detailed comparisons with backgrounds, including those from MSSM cascade decays are made, using the PYTHIA event simulator., Comment: 47 pages, 22 figures; v2 matches JHEP version